Table of Contents
Introduction ....................................... . . . . . .............................................................1
Examining a field .................................................................................................. 2
Tips for shipping to diagnostic laboratories ................................................................ 2-3
Stage I: Scouting from emergence to knee-high ............................................................. 4
Stage II: Scouting from knee-high to tasseling .............................................................. 11
Stage III: Scouting from tasseling to maturity ................................................................ 16
Disease symptoms .............................................................................................. 24
Leaf diseases ................................................................................................ 24-26
Smutting diseases ...................................................... . . . . ..................................... 26
Virus and virus-like diseases ...................................................... . . . . ......................... 27
Fungal systemic diseases .......................................... . . . ..................................... 27-28
Stalk and root rot diseases ................................................................................. 28-29
Ear and kernel rots ...................................................... . . .................................. 29-30
Insect injury symptoms and management recommendations ....................... . . . . . . . ......... 31-39
Herbicide injury symptoms ................................................................................. 40-42
Herbicides that may be used or trigger symptomology in corn ....................................... 43-47
Herbicides listed by active ingredient and mode of action ............................................ 48-51
Nutrient deficiency symptoms ............................................................................. 52-53
Index ............................................................................................................... 54
Introduction
This manual is prepared and distributed by Monsanto Company to help farmers, seed dealers, and company
personnel determine the likely causes of abnormal corn plant appearance. While the primary target is the North
American Region, the principles and many of the situations described in this publication extend to the regions of the
world where corn is grown.
Symptoms may be due to a single cause or the result of two or more interacting factors. Also, because of their
different genetic backgrounds, different hybrids may not have identical symptoms in response to the same
cause. Routine field examinations are crucial in spotting problems or potential problems. Some growers employ
professional crop scouts rather than perform this function themselves. Weekly examinations are generally
sufficient.
Once a problem has been identified, its extent and severity must be determined to decide whether corrective
action is necessary. Many pest management recommendations include threshold levels when control measures
will return a profit. Consult Cooperative Extension Service and chemical company recommendations for control
measures.
1
Corn Diagnostic Guide
1
Diagnosing Field
Problems in Corn
EXAMINING A FIELD
Carry the appropriate tools to help effectively scout or monitor fields. Some basic tools to have on hand include:
•
•
•
•
•
Tape measure
Knife
Trowel (6 or 8 inch)
Magnifying glass
Clipboard and record keeping materials
•
•
•
•
•
Small plastic bags
Water source
Paper towels
Calculator
Field marking flags
A spade and a set of nesting pails may be useful if considerable digging is expected. Digital cameras can be
helpful in getting a record of insects or disease symptoms.
Be very careful when making area-to-area or field-to-field comparisons. Many factors can influence appearance,
including: soil type, slope, and drainage; previous crops; fertility practices; seedbed preparation; date, depth,
and rate of planting; pest control; seed lot; and hybrid.
Look for positives, not just problems. Observe and note hybrid differences, as well as the effects of fertilizer and
cultural practices.
The following diagnostic key separates plant growth into three primary stages of crop development:
Stage I
Emergence to knee-high
Stage II
Knee-high to tasseling
Stage III
Tasseling to maturity
In the field, onset of symptoms might occur earlier or later than indicated, and may be observed during more
than one growth stage.
TIPS FOR SHIPPING TO
DIAGNOSTIC LABORATORIES
Trained, experienced agronomists, crop protection,
research, and sales personnel stand ready to assist you
in diagnosing field problems. Local seed dealers are your
first contact when questions arise. Positive diagnosis
often requires identification or confirmation of causes
by a diagnostic laboratory. Most states have some
arrangement, usually through their Cooperative Extension
Service office, for accessing expert diagnosis.
Some of these are more formally conducted than others,
and cost of the service varies. Also, there are a few private
laboratories that are equipped to provide such services.
Your local Cooperative Extension Service office can
suggest companies and provide contact information.
When preparing plant or soil samples for a diagnosis,
follow these instructions offered by the laboratories.
2
1. Provide representative samples of each problem
observed, as well as a healthy sample from unaffected
plants or plant parts.
2. If sending leaf tissue, place sections of leaves showing
disease symptoms between pieces of dry paper
toweling or notebook paper.
area twice, on dates about a week apart, to
determine whether the problem is intensifying,
spreading, or disappearing.
•
Crop symptoms as observed in the field, such
as “plants were wilted” or “leaves appeared
spotted.” Describe the size of area affected:
spots, strips, or the entire field.
•
Percentage of plants affected.
•
Soil type (clay, sand, muck, etc.).
•
Topography around affected plants, such as
high ground, low ground, or gently sloping.
5. Use a sturdy envelope or box for shipping.
•
6. Avoid shipping at times that are likely to result in the
parcel lying in a post office or freight depot over a
weekend or holiday. Overnight delivery, early in the
week, is strongly recommended.
Fertility level (include a soil test report, if
available) and the amount, kind, and timing of
fertilizer application.
•
Pesticides applied (fungicides, herbicides,
insecticides, application rate, and date).
•
Soil moisture situation at and since planting. If
the field was irrigated, indicate the amount and
dates of water application.
•
Unusual recent air temperatures or humidity
conditions.
•
Previous cropping and tillage history.
•
Types of weeds in the field.
3. If sending the whole plant, remove excess soil from
the roots and wrap the roots in moist paper toweling.
Put roots and towel in a plastic bag. Do not place the
entire plant in a plastic bag. Wrap stem and leaves
with paper, foil, or cardboard.
4. Do not add water or crush specimens unnecessarily.
7. Information will need to be provided with the plant
specimen. Often, laboratories have specific forms that
are required when submitting a sample. Information
requested on such forms often includes the following:
3
•
Variety (hybrid number) of crop.
•
Location where sample was taken (county,
township, and town)..
•
Date of planting, date problem was first
observed, and date sample was collected.
Indicate whether the problem is better or worse
than when first observed. Visit a problem
Corn Diagnostic Guide
2
Stage I: Scouting from
Emergence to Knee-High
Determine the extent and severity of any problem identified. Is the problem throughout the field or spotty and
localized? Has emergence been completed or are there seeds sprouted, ready to emerge? Take accurate stand
counts and determine percent of stand achieved.
If replanting is necessary, take steps to prevent recurrence of the cause for poor emergence. Verify that the
planter is operating properly and that fertilizer or pesticide issues have been corrected.
% stand achieved =
number of plants established
number of seeds planted
X 100
If the stand is uneven or if there are skips down the row,
dig to find the planted seed and its distribution.
GENERAL SYMPTOM POSSIBLE CAUSE
REMARKS
1. No seed
•
Planter
Improper adjustment; row unit drive not
engaged; worn parts; clogged spout; empty
box or tank; wrong plates, disks, or drum;
excess or wrong seed treatment.
•
Rodents or birds
Digging and partly-eaten kernels.
2. Normal seed
appearance; not
swelled
•
Unfavorable soil conditions
Cold, dry soil.
•
Poor seed-soil contact
Inadequate press wheel pressure; improper
closing wheel adjustments; inadequate residue
management; dry or cloddy soil.
3. Normal seed
appearance; swelled
but not sprouted
•
Unfavorable soil conditions
Cold, wet soil.
•
Fertilizer or pesticide injury
Phytotoxic pesticides or too much fertilizer too
close to the seed.
4. Seed dead, rotted
•
Seed rots or seedling blights
These are accentuated when soil conditions
are unfavorable for germination and seedling
growth. Many species of fungi and/or bacteria
may be involved. Fungicide seed treatment
protects the seed, not the seedling.
4
GENERAL SYMPTOM POSSIBLE CAUSE
REMARKS
4. Seed dead, rotted
(cont.)
•
Fertilizer injury
Fertilizer salts, nitrogen, and potassium draw
moisture and may leave seed in soil too dry
to support growth. In-furrow applications are
more likely to cause fertilizer injury than starter
fertilizers placed at least 2 inches from the seed.
Ammonia toxicity is caused when planting
follows anhydrous or aqua ammonia application
too closely or where application was too
shallow. This can kill or stunt seedlings. Roots
appear sheared off. Boron and some other
micronutrients impair germination if they are too
close to the seed.
•
Insecticide injury
Some soil-applied organophosphate
insecticides can impair germination if placed
in furrow with the seed. Check the label and
apply only as directed.
•
Dead seed planted
•
Unfavorable soil conditions
Cold, dry, wet, or crusted soil.
5. Seed hollowed out
•
Insects
Seed corn beetle, seed corn maggot, or
wireworm (see pp. 36-38).
6. Sprout twisted or
leaves expanded
below ground
•
Unfavorable soil conditions
Crusted, cold, or cloddy soil. A cloddy surface
can allow light to reach the sprout and trigger
leafing too soon. In the case of crusting, rotary
hoeing may be beneficial.
•
Seed planted too deep
•
Mechanical injury to seed in
handling or planting
•
Chemical injury
Fertilizer (see p. 5); insecticides (see p. 5); or
some herbicides such as acetanilides and
dinitroanilines (see pp. 41-42).
•
Planter
Seed injury due to improper operation or
adjustment, including planting depth.
•
Unfavorable soil conditions
Cold, dry, wet, or crusted soil. In the case of
crusting, rotary hoeing may be beneficial. Properly
banded fertilizer at planting may help seedlings
overcome unfavorable soil conditions.
•
Seed planted too deep
7. Slow, uneven
emergence
5
Corn Diagnostic Guide
If plants are abnormal in appearance,
try to identify one of the following specific symptoms.
GENERAL SYMPTOM POSSIBLE CAUSE
REMARKS
1. Seedlings pulled or
dug up, seed eaten
•
Bird or rodent damage
Chemical repellents may help.
2. Slow, uneven plant
growth
•
Unfavorable growing conditions
Cold, dry, wet, or compacted soil. Properly
banded fertilizer at planting may help minimize
the effects of some unfavorable growing
conditions.
•
Low fertility
If a nutrient deficiency due to inadequate
amounts in the soil, is confirmed, consider
sidedressing or foliar application, depending on
the nutrients involved (see pp. 52-53).
•
Insects attacking roots
Corn root aphid, corn rootworm, grape colaspis,
webworm, white grub, or wireworm (see pp.
31-38).
•
Nematodes attacking roots
Requires microscopic analysis.
•
Chemical injury
Fertilizer (see p. 5); insecticides (see p. 5);
herbicides such as Balance®; Command® or
Scepter® carryover (see pp. 41-42); or liquid
manure.
•
Non-uniform planting depth
•
Dry, loose soil is not conducive to normal root
Failure of secondary roots to
develop (rootless corn syndrome) development. This condition is accentuated
by shallow planting and whipping by wind.
Cultivation may help by throwing soil around the
base of plants.
•
Nutrient deficiency
Magnesium, nitrogen, phosphorus, or sulfur
(see pp. 52-53). Nitrogen deficiency results in
a yellow discoloration of leaves. Phosphorus
deficiency results in a purpling of leaves due to
the accumulation of anthocyanins. If nutrient
deficiency is confirmed, consider sidedressing
or foliar application, depending on the nutrients
involved.
•
Unfavorable soil conditions
Waterlogged, cold, or compacted soil. These
conditions can also affect nutrient uptake and
translocation.
3. Discolored leaves
6
GENERAL SYMPTOM POSSIBLE CAUSE
REMARKS
3. Discolored leaves
(cont.)
•
Insects attacking roots
Most observed leaf discoloration is due to
nutrient deficiency induced by damaged or
inadequate roots (see nutrient deficiency,
above).
•
Nematodes attacking roots
Requires microscopic analysis.
•
Chemical injury
Fertilizer (see p. 5); insecticides (see p. 5);
herbicides such as Balance®; Command®
or Scepter® carryover (see pp. 41-42); liquid
manure.
•
Wind damage
Abrasion by sand or soil particles. Difficulty
establishing secondary roots.
•
Frost or freeze
Check growing point for damage. Seedlings
often recover. Most pronounced in low-lying
areas.
•
Cold (not freezing) temperature
stress
Cool nights and warm days promote aboveground plant growth at the expense of root
development. This leads to increased demand
by the above ground tissues for more nutrients
than the roots can deliver. The result can be
short-term deficiency symptoms until the root
system becomes more developed.
•
Anhydrous burn
•
Mechanical injury
•
Hybrid differences
Uneven Corn Plant Growth
7
Corn Diagnostic Guide
GENERAL SYMPTOM POSSIBLE CAUSE
4. Leaves rolled or
puckered, may be
wilted
•
Drought
•
Insects attacking roots or stalks
See Section 6, Insect Injury Symptoms (p.
31-38), plus chinch bug, cutworm, Japanese
beetle, stink bug, or webworm.
•
Nematodes attacking roots
Requires microscopic analysis.
•
Mechanical root pruning
5. Leaves rolled or
•
twisted together
(“onion leaf” or “buggy •
whip”)
6. Shredded leaves or
eaten plants
7. Leaves spotted,
striped or dead
REMARKS
Herbicide injury
Acetanilides, dinitroanilines, or phenoxys (see
pp. 41-42).
Temperature variation
Alternating hot and cold weather, inducing
very rapid growth spurts followed by little or no
growth.
•
Nutrient imbalance
Boron toxicity or calcium deficiency (see p. 52).
•
Hail damage
Injury to the growing point at this growth stage can
result in short-term wrapping of leaves.
•
Wind damage
•
Hail damage
•
Insects
Armyworm, common stalk borer, corn earworm,
cutworm, European corn borer, grasshopper,
slug, or webworm (see pp. 32-37).
•
Livestock or wild animal grazing
Look for tracks.
•
Wind damage
Abrasion by sand or soil particles.
•
Low soil pH
Beaded streaking of leaves, which turn reddishpurple and may die.
•
Nutrient deficiency
Boron, copper, magnesium, potassium, sulfur, or
zinc (see pp. 52-53).
•
Insects
Flea beetle, leaf miner, or thrips (see pp. 35-37).
•
Disease
Anthracnose, bacterial wilt, eyespot, Goss’s wilt,
holcus spot, seedling blights (favored by cool, wet
soil), virus or virus-like diseases (see pp. 24-27).
•
Fertilizer or herbicide injury
Anhydrous burn; spray drift; foliar-applied
herbicides such as Buctril®, Basagran®,
Gramoxone®, or Blazer®; Classic®, Scepter®, or
Reflex® carryover; premix acentanilides postapplied (see pp. 40-42).
•
Sunscald or cold
Cold nights followed by clear, bright, fast-warming
days.
•
Hybrid differences
8
GENERAL SYMPTOM POSSIBLE CAUSE
REMARKS
8. Rows of holes across
leaves
•
Insects
Billbug, common stalk borer, corn borer,
cutworm, or stink bug (see pp. 32-37).
9. Plants wilt and die
suddenly
•
Insects
Billbug, chinch bug, cutworm, stink bug, white
grub, or wireworm (see pp. 32-38).
•
Wind damage
•
Disease
Seedling blights, bacterial wilt, or Goss’s wilt
(see p. 26).
•
Herbicide injury
Triazines or misapplications of glyphosate
herbicides (see pp. 41-42).
•
Frost or freeze
Check growing point for damage. Seedlings
often recover.
•
Lightning
Kills everything, usually in circular area.
•
Anhydrous burn
•
Flooded, water-logged soil
“Buggywhip”
Corn plant two days after frost
9
Corn Diagnostic Guide
GENERAL SYMPTOM POSSIBLE CAUSE
REMARKS
10. Plants twisted or
broken off
11. Inhibited root
development or
malformed roots
•
Herbicide injury
Especially 2,4-D followed by wind (see pp. 4142).
•
Insects
Billbug, cutworm, lesser cornstalk borer, or
stinkbug (see pp. 32, 36-37).
•
Nematode injury
Requires microscopic analysis.
•
Insects
Corn rootworm, grape colaspis, white grub, or
wireworm (see pp. 34-38).
•
Fertilizer injury
•
Herbicide injury
Phenoxys, Banvel®, carryover dinitroanilines, and
Scepter® or Classic® carryover (see pp. 41-42).
•
Soil conditions
Planting when soils are too wet can cause
sidewall compaction that can arrest or severely
restrict corn root development. Look for flatsided or abruptly arrested root systems.
Wind Damage in Corn Field
Hail Damage in Corn Field
10
3
Stage II: Scouting from
Knee-High to Tasseling
This is the period of most rapid plant growth. Nutrient and moisture demands are high; deficiencies will likely
reduce crop yield potential. Problems must be evaluated for economic damage potential before control
decisions can be made. Observe differences due to hybrids and management practices.
If plants are abnormal in appearance,
try to identify one of the following specific symptoms.
GENERAL SYMPTOM POSSIBLE CAUSE
REMARKS
1. Uneven height (tall
plants, short plants)
Uneven planting depth; uneven soil moisture.
2. Numerous tillers
3. Discolored or dead
leaves
11
Corn Diagnostic Guide
•
Emerged at different times
•
Varied nutrient or moisture
availability under drought
conditions
•
Low soil pH
•
Herbicide drift
•
Nutrients concentrated at dry soil Nutrients are unavailable to the plant.
surface
•
Fallow (idle land) syndrome
Phosphorus is unavailable to the plant (see p.
53).
•
Growing point injury
Mechanical or insect damage.
•
Favorable early-season growing
conditions
Optimum moisture, high soil fertility, or both.
•
Low plant population
•
Adjacent to open spaces
(population gaps) in the row
•
Hybrid differences
•
Disease
Crazy top (see p. 27)
•
Nutrient deficiency
Nitrogen, phosphorus, or potassium (see p.
53).
Use of burndown products adjacent to cropped
area.
GENERAL SYMPTOM POSSIBLE CAUSE
REMARKS
3. Discolored or dead
leaves (cont.)
4. Whorl leaves dead
(“deadheart”)
5. Leaves spotted or
striped
•
Fertilizer or herbicide injury
Fertilizer or herbicide on foliage. This tends
to be more pronounced at row ends or where
overlap application was made.
•
High temperatures
Noted as scalding or bleaching of top leaves
first.
•
Sunscald or cold banding
Cold nights followed by clear, bright, fastwarming days.
•
Insects
Chinch bug, spider mite, or root-attacking
insects, which can reduce nutrient uptake (see
pp. 32-37).
•
Mechanical injury
•
Frost or freeze
•
Hybrid differences
•
Barren stalk
Purpling or reddening due to anthocyanin
expression in response to accumulation of
sugars that cannot translocate to the initiating
ear.
•
Disease
Bacterial stalk rot (see p. 28).
•
Insects
Billbug, corn borer, or fall armyworm (see pp.
32-33).
•
Chemical injury
More common following a late over-the-top
application of certain herbicides.
•
Excessive heat
Temperature exceeding 100°F, depending on
moisture availability and genetics of the hybrid.
•
Low soil pH
Beaded streaking of leaves, which turn reddishpurple and may die.
•
Nutrient deficiency
Boron, iron, magnesium, manganese, nitrogen,
or potassium (see p. 52-53).
•
Chemical injury
Herbicides, additives’ reactions, or fertilizers;
symptoms may be due to spray drift on foliage.
•
Disease
Bacterial leaf blight, eyespot, Goss’s wilt, holcus
spot, leaf blights, Physoderma brown spot,
rust, sorghum downy mildew, virus or virus-like
diseases (see pp. 24-28).
• Insects
Cereal leaf beetle, corn rootworm beetle,
corn blotch leaf miner, flea beetle, spider
mite, or thrips; root-damaging insects
induce nutrient deficiency or drought
symptoms (see pp. 32-37).
12
GENERAL SYMPTOM POSSIBLE CAUSE
REMARKS
5. Leaves spotted or
striped (cont.)
Abrasion by sand or soil particles.
•
Wind damage
•
Hail damage
•
Genetic stripe
Observed only on occasional plants.
•
Sunscald or cold banding
Cold nights followed by clear, bright, fastwarming days.
•
Livestock or wild animals
Look for tracks.
•
Insects
Armyworm, billbug, common stalk borer, corn
borer, corn earworm, cutworm, grasshopper,
Japanese beetle, leaf miner, slug, or wireworm
(see pp. 32-38).
•
Hail damage
Determine if the growing point survived. If it did
not, plant will not produce a tassel. Despite this,
ear fertilization may still occur.
•
Wind damage
•
Disease
Sorghum downy mildew (see p. 28).
7. Plants stunted, leaves
close together with
mosaic mottle or
streaks; leaves yellow
or red
•
Virus or virus-like diseases
Corn lethal necrosis, corn stunt spiroplasma,
maize chlorotic dwarf, or maize dwarf mosaic
(see p. 27).
8. Gray or black galls
growing on plants
•
Disease
Common corn smut (see p. 26).
9. Stalks spindly,
unthrifty, yellow
•
Nutrient deficiency
See pp. 52-53.
•
Excess soil moisture
•
Excessive plant population
•
Root damage
Insects, nematodes, chemical, or mechanical.
•
Stalk damage
Insects, disease, or mechanical.
•
Drought
•
Root damage
Insects, nematodes, chemical, or mechanical.
•
Stalk damage
Mechanical or insects; chinch bug, common stalk
borer, or corn borer (see pp. 32-33).
•
Chemical injury
2,4-D and other phenoxy herbicides; Banvel® (see
p. 41).
•
Cold soil during seedling stage
6. Leaves eaten or
shredded
10. Plants wilted or rolled
11. Top leaves tightly
rolled (“buggy whip”
or “onion leafing”)
13
Corn Diagnostic Guide
GENERAL SYMPTOM POSSIBLE CAUSE
REMARKS
11. Top leaves tightly
rolled (“buggy whip”
or “onion leafing”)
(cont.)
•
Temperature response or rapid
growth syndrome
Alternating hot and cold periods, speeding and
slowing plant growth.
•
Nutrition
Boron toxicity or calcium deficiency (see p. 52).
•
Mechanical injury
•
Hybrid differences
•
Recovery after root damage
•
Recovery after early season
environmental conditions
•
Wind and wet soils
•
Dry, hot soil surface
•
Wind action
14. Plants twisted or
growing off at 90˚
angle
•
Mechanical injury
15. Plants leaning or
broken off
•
Wind damage
Especially if soil is wet. Wind can cause
greensnap at lower nodes of rapidly growing
stalk.
•
Livestock or wild animals
Look for tracks.
•
Root damage
Insects, nematodes, chemical, or mechanical.
•
Insects attacking stalk
Common stalk borer or corn borer (see p. 32-33).
•
Chemical injury, especially if
followed by wind
Especially Banvel® or phenoxy herbicides (see
pp. 39-41).
•
Soil compaction
Inadequate root development.
•
Poor secondary root
development in dry soil
Rootless corn syndrome due to weather and
aggravated by shallow planting.
•
Disease
Bacterial or Pythium stalk rots (see pp. 28-29).
•
Hail damage
•
Lightning
Kills everything, usually in a circular area.
•
Drought
Field areas with low water-holding capacity are first
to show stress.
12. Plants growing up in a
curved “gooseneck”
13. Curled or stubby
brace roots
16. Plants wilt and die
suddenly
Insects (usually, but not limited to corn rootworm
larvae), nematodes, herbicides (especially
phenoxys), soil compaction, mechanical injury,
or wind.
14
GENERAL SYMPTOM POSSIBLE CAUSE
REMARKS
16. Plants wilt and die
suddenly (cont.)
Bacterial or Pythium stalk rots (see pp. 28-29).
•
Disease
•
Frost or freeze
•
Herbicide injury
Misapplication of glyphosate, glufosinate,
paraquat, or other non-selective herbicides (see
pp. 41).
17. Tassel feeding (while
in whorl)
•
Insects
Armyworm, corn leaf aphid, or western bean
cutworm (see pp. 32-35).
18. Tassels proliferated
into green cluster of
fingerlike branches,
excessive tillering,
leaves often thick and
straplike
•
Disease
Crazy top (see p. 27).
19. Tassel proliferated,
with stringy black
vascular bundles
present
•
Disease
Head smut (see p. 26).
“Greensnap” at lower nodes of rapidly growing corn stalk
15
Corn Diagnostic Guide
4
Stage III: Scouting from
Tasseling to Maturity
This period, which commences with the critical pollination stage, includes grain fill, plant maturation, and death.
It also includes the critical stage before harvest when standability and ear retention become concerns. Field
observations are essential to detect yield-depressing factors during this period.
If LEAVES are affected,
try to identify one of the following specific symptoms
GENERAL SYMPTOM POSSIBLE CAUSE
REMARKS
1. Eaten
2. Shredded
3. Dead “frosted”
appearance
4. Spotted or dead
5. Discolored sheath
•
Livestock or wild animals
Look for tracks.
•
Insects
Armyworm, corn borer, corn rootworm beetles,
grasshopper, or Japanese beetle (see pp. 32-36).
•
Hail damage
•
Wind damage
•
Disease
•
Frost or freeze
•
Drought
•
Disease
Anthracnose, leaf blights, or stalk and root rots
(see pp. 24-26; 28-29).
•
Insects
Corn borer, corn leaf aphid, or spider mite (see
pp. 31-33; 37).
•
Disease
Numerous leaf blights such as anthracnose,
eyespot, Goss’s wilt, gray leaf spot,
Helminthosporium leaf spot, northern corn leaf
blight, Phaeosphaeria leaf spot, Physoderma
brown spot, rust, or southern leaf blight (see p.
26).
•
Chemical injury
Especially spray drift.
•
Insects
Corn leaf aphid (see p. 31).
•
Disease
Purple sheath spot caused by saprophytic
organisms existing on pollen trapped between
the leaf sheath and stalk.
Sorghum downy mildew (see p. 28).
16
GENERAL SYMPTOM POSSIBLE CAUSE
6. Red or purple color
7. White striping with
white, downy growth
on upper and lower
leaf surfaces
REMARKS
•
Mechanical injury
•
Barren plant
Anthocyanins develop in response to
accumulation of sugars that cannot be
translocated to filling grain.
•
Disease
Corn rust, corn stunt spiroplasma, high plains
virus, or maize chlorotic dwarf (see pp. 24-27).
•
Insects
Corn borer (see p. 33).
•
Hybrid differences
•
Disease
Sorghum downy mildew (see p. 28).
If SILKS are affected,
try to identify one of the following specific symptoms
GENERAL SYMPTOM POSSIBLE CAUSE
REMARKS
1. Eaten off
•
Insects
Armyworm, corn earworm, corn rootworm
beetle, grasshopper, Japanese beetle, or
western bean cutworm (see pp. 32-35).
2. None visible, or
delayed several days
after tasseling
•
Heat
•
Drought
•
Nutrient deficiency or imbalance
Especially nitrogen or phosphorus.
•
Temperature variation
Cold nights occurring just prior to silking.
•
Insects
Corn leaf aphid, fall armyworm, or spider mite
(see pp. 31-32; 37).
•
Excessive population for
conditions
•
Drought
•
Nutrient deficiency or imbalance
•
Temperature variation
•
Hybrid differences
Cold nights during early silking.
•
Hybrid differences
Fresh silk color is genetically controlled.
3. Trapped, balled within
the husk
4. Red or green color
17
Corn Diagnostic Guide
See pp. 52-53.
If TASSELS are affected,
try to identify one of the following specific symptoms
GENERAL SYMPTOM POSSIBLE CAUSE
1. Failed to emerge
REMARKS
•
Drought or heat stress
•
Nutrient deficiency
Especially boron (see p. 52-53).
•
Insects
Aphid stress, corn earworm, or fall armyworm
(see pp. 31-32).
2. A mass of leaves
•
Disease
Crazy top, head smut, or sorghum downy
mildew (see pp. 27-28).
3. One or more small
ears formed
•
Genotype by environment
interaction
Most common on tillers.
4. Kernels develop in
tassel
•
Genotype by environment
interaction
Most common on tillers.
5. Broken off, stalk
tunneled
•
Insects
Corn borer (see p. 33).
If STALKS are affected,
try to identify one of the following specific symptoms
GENERAL SYMPTOM POSSIBLE CAUSE
1. Red or purple color
2. Barren (no ear
enlargement)
•
Mechanical injury to plant
•
Barren stalk
•
Hybrid differences
•
Insects
•
Drought
•
Heat
REMARKS
Anthocyanins develop in response to
accumulation of sugars that cannot be
translocated to filling grain.
When corn borers tunnels into a stalk, the area
above the point of entry may turn red or purple.
18
GENERAL SYMPTOM POSSIBLE CAUSE
REMARKS
2. Barren (no ear
enlargement) (cont.)
3. Broken below ear
4. Broken above ear
5. Multiple ears at one
node
19
Corn Diagnostic Guide
•
Nutrient deficiency or imbalance
See pp. 52-53.
•
Insects
Corn leaf aphid or spider mite (see pp. 31, 37).
•
Silks eaten off prior to pollination
Corn rootworm beetle and Japanese beetle
(see pp. 34-36).
•
Disease
Head smut, mildews, virus or virus-like disease
(see pp. 26-27).
•
Excess population for conditions
•
Tillers
Seldom produce a fully-developed ear.
•
Timing of silk or pollen shed
disrupted
Environmental stress.
•
Mechanical injury
•
Wind
Plants just prior to tasseling are especially
vulnerable to greensnap by wind.
•
Disease
Stalk and root rots (see pp. 28-29).
•
Nutrient imbalance
Excess nitrogen, insufficient potassium (see p.
53).
•
Insects
Southwestern corn borer (see p. 33).
•
Weather stress
Drought, heat, or other conditions limiting
photosynthesis.
•
Mechanical injury
Machinery; livestock or wild animals.
•
Excessive population for
conditions
•
Delayed harvest
•
Wind
•
Insects
European corn borer or fall armyworm (see pp.
32-33).
•
Mechanical injury
Machinery; livestock or wild animals.
•
Delayed harvest
•
Hybrid differences
•
Mechanical injury
•
Cold temperature when ears
formed
•
Disease
Mildews, virus or virus-like disease (see pp. 2728).
GENERAL SYMPTOM POSSIBLE CAUSE
REMARKS
5. Multiple ears at one
node (cont.)
•
Insects
Results from severe silk clipping by insects such
as corn rootworm beetle and Japanese beetle
(see pp. 34, 36).
6. Leaning, but not
broken (root lodged)
•
Wind and wet soil
•
Poor root development
Drought, fertilizer placement, soil compaction,
low soil pH, or poorly drained soil.
•
Insects
Corn rootworm and other root feeders (see pp.
34-35).
•
Nematode activity
•
Disease
Stalk and root rots (see pp. 28-29).
•
Nutrient deficiency
Especially potassium (see p. 53).
•
Herbicide injury
Especially 2,4-D and other phenoxys (see p. 41).
•
Mechanical injury
Machinery, livestock or wild animals
•
Delayed harvest
•
Hybrid differences
•
Disease
Leaf blights or stalk and root rots (see pp. 2426, 28-29).
•
Insects
Corn borer (see p. 34).
•
Frost or freeze
•
Severe drought
•
Lightning
Kills everything, usually in a circular area.
•
Saprophytic
Buildup on dead stalk tissue under warm, humid
weather conditions. Timely harvest will deter.
7. Premature death
8. Black mold
If EARS are affected,
try to identify one of the following specific symptoms
GENERAL SYMPTOM POSSIBLE CAUSE
REMARKS
1. Numerous ear shoots,
leafy and barren
Crazy top, sorghum downy mildew, virus or
virus-like diseases (see pp. 27-28).
•
Disease
20
GENERAL SYMPTOM POSSIBLE CAUSE
REMARKS
2. Soft, glistening smut
•
galls, black and
powdery when mature
Disease
Common corn smut (see p. 26).
3. Poorly filled tips
•
Hybrid differences
•
Nutrient deficiency
•
Interaction between population,
hybrid, and environment
•
Insects
Silks clipped before pollination. Corn borer, corn
earworm, corn rootworm beetle, fall armyworm,
or Japanese beetle (see pp. 33- 36).
•
Disease
Foliar disease that reduce photosynthesizing
area (see pp. 24-26).
•
Drought
Silks at ear tips were not present when pollen
was available
•
Unusually favorable growing
conditions after pollination
Cob elongates, but rarely fills up tip kernel.
•
Suboptimum light, carbon
dioxide, or temperature during
kernel fill
Reduced photosynthesis; tip kernels abort.
Nutrient deficiency
Especially nitrogen and phosphorus (see p. 48).
4. Small malformed, light •
weight
•
5. Very short husk,
remains tight at
maturity; ear tip
exposed
21
Corn Diagnostic Guide
Especially nitrogen or potassium (see p. 53).
Drought or heat stress
•
Plant damage
•
Excessive population for
conditions
•
Second or third ear on stalk, or
on a tiller
•
Insect-caused plant stress
Numerous ear-feeding insects (see pp. 32-38).
•
Disease
Leaf blights, stalk and ear rots, virus or virus-like
diseases (see pp. 24-30).
•
Soil compaction
•
Weather
•
Hybrid differences
Mechanical or disease.
Usually observed after drought or heat has
stopped husk growth, but later favorable
conditions permit more normal ear size to
develop.
GENERAL SYMPTOM POSSIBLE CAUSE
REMARKS
6. Barren (little to no
grain)
•
Disease
Head smut, virus or virus-like diseases (see pp.
26-27).
•
Pollination failure
Drought, heat, or other stress interfered with
silk/pollen shed timing; insect (clipped silks
or caused tassel to abort); chemical injury
(especially by growth regulators like 2,4-D and
Banvel®).
•
Pesticide injury
Following drift or misapplications.
7. Pinched ear syndrome •
Chilling injury during early ear
development
Also called beer can ear. Ear is reduced to
3-4 inches. Well filled kernels are on bottom
third of ear, cob tissue on middle third, and
undeveloped tissue on top third.
8. Dropped
•
Drought
Weakened shank.
•
Nutrient deficiency
Weakened shank.
•
Hybrid differences
Ears usually drop free of husk.
•
Insect damage to shank
Husk usually remains on the dropped ear;
European corn borer (see p. 33).
•
Lack of adequate viable pollen
when silks are receptive
•
Silks eaten off before pollination
•
Heat or drought at pollination
•
Nutrient deficiency
•
Herbicide injury
Phenoxy herbicides or too-late applications of
glyphosate (see p. 41).
•
Insects
Corn borer, corn earworm, fall armyworm, picnic
beetle, or western bean cutworm (see pp. 3335).
•
Birds, animals
9. Scattered kernel set
10. Kernel feeding
11. Rotten (spots or entire •
ear)
Insect or animals.
Disease
Ear and kernel rots or Helminthosporium leaf
spot (see pp. 29-30; 25).
•
Insects
Corn borer, corn earworm, fall armyworm, picnic
beetle, or western bean cutworm (see pp. 33-35).
Followed by weathering or disease.
•
Birds
Followed by weathering or disease.
•
Hail or other mechanical injury
Followed by weathering or disease.
22
GENERAL SYMPTOM POSSIBLE CAUSE
12. Kernels eaten from
ear tips
13. Tunnels in ear, cob,
shank, or stalk
REMARKS
•
Birds
•
Wild animals or rodents
•
Insects
Corn earworm, fall armyworm, picnic beetle, or
western bean cutworm (see pp. 33-35).
•
Insects
Corn borer, corn earworm, or fall armyworm (see
pp. 32-33).
If KERNELS are affected,
try to identify one of the following specific symptoms
GENERAL SYMPTOM POSSIBLE CAUSE
REMARKS
1. Broken seedcoat,
“popped” appearance
•
Genetic and environment
interaction
Popped kernels usually occur under high
temperatures.
2. Horizontally cut or
split seedcoat
•
Silk-cut
A genetic and environment interaction. Not
visible until kernels are shelled from the cob.
3. Pink or red streaking
or lengthwise stripes,
especially running
over crown
•
Kernel red streak
Caused by toxin secreted during feeding of
wheat curl mite. More pronounced toward ear
tip. No detrimental effects are known.
4. Sprouted especially at
base of ear
•
High rainfall and warm
temperature while ear remained
erect on stalk
Usually accompanied by mold.
5. White streaking, also
known as “starburst”
•
Disease
Associated with Fusarium ear rot.
Barren corn
23
Corn Diagnostic Guide
Pinched ear syndrome
5
Disease Symptoms
This section will help you identify the common corn diseases based on plant symptoms and conditions. It is not
uncommon to have symptoms of several different diseases present at the same time. Symptoms of different
diseases may appear similar, particularly during early stages of disease development. Laboratory culturing and
microscopic examination may be required to make a positive identification.
Growth stages during which symptoms generally appear are listed following the disease name and are described
as follows:
Stage I
Stage II
Stage III
Emergence to knee-high
Knee-high to tasseling
Tasseling to maturity
LEAF DISEASES
Anthracnose (Stage I, III)
Oval to spindle-shaped
water-soaked lesions on
youngest leaves turn tan to
brown with yellow to reddish
brown borders. Heavily
infected leaves wither and
die. Top-leaf die-back may
occur 4 weeks to 6 weeks
after pollination, leaving
the lower stalk green. The
organism thrives in warm, humid weather. The stalk-rot
phase of the organism is of greater concern than the leaf
blight phase.
Bacterial Wilt and Bacterial Leaf Blight
(Stewart’s Wilt, Stewart’s Disease) (Stage I, III)
Young plants exhibit long,
green-gray, water-soaked
lesions with wavy margins,
accompanied by stunting
and wilting which lead to
plant death. Cavities may
form in stalk near the soil line.
Bacterial masses ooze from
cut end of infected stalks or
leaves.
The more common leaf blight phase appears after
tasseling. Leaves are streaked with gray-green to yellowgreen lesions, each distinguished by the presence of a flea
beetle feeding scar toward the base of the streak. Streaks
are long and irregular, turning tan as the tissue dies.
Flea beetles (small, oval, black insects) are the primary
carrier. Incidence of the disease is relative to beetle
population. Sweet corn tends to be more sensitive than
field corn to this disease.
Common Corn Rust (Stage II, III)
Cinnamon-brown, powdery,
circular-to-elongated pustules
(blister-like growths) can
occur on any aboveground
plant tissue, but especially
on both surfaces of the
leaves. In contrast, pustules
of southern corn rust occur
primarily on the upper leaf
surface. Pustules rupture
leaf surface and rusty “powder” can be rubbed off with
fingers. Pustules become dark brown to black late in the
growing season. The organism thrives in moderate to cool
temperatures and high humidity.
24
Eyespot (Stage II, III)
Small (less than ¼ inch),
circular, translucent lesions
surrounded by a yellow to
purple margin, give a halo
effect. Lesions occur on
leaves (most commonly as
plants approach maturity),
sheath and husk. The
disease is favored by cool,
moist weather.
Goss’s Wilt
(Leaf Freckles and Wilt, Nebraska Bacterial
Wilt and Leaf Freckles) (Stage I, III)
Helminthosporium Leaf Spot
(Northern Leaf Spot) (Stage III)
Numerous races of the
organism have been
identified. Symptoms vary
by race. Lesions tend to
be oblong to blocky, and
tan to brown in color. This
leaf spot may also cause a
black, charred-appearing
ear rot. It prefers moderate
temperatures and high
humidity.
Holcus Spot (Stage I)
Young plants wilt and
die. Vascular bundles are
discolored. More common
later-season infections
produce dull gray-green
to orange lesions forming
water-soaked streaks with
irregular margins on leaves.
Within developing lesions,
small, irregular shaped watersoaked “freckles” appear. Bacterial droplets may ooze
from the leaf surface early in the morning. Plant injury,
such as from hail or wind damage, enhances infection.
This organism causes small,
circular to oblong, watersoaked lesions toward tips
of lower leaves. Later, lesions
become creamy white to
tan, then light brown with
reddish margins. Holcus spot
is very similar in appearance
to paraquat damage.
Rainstorms accompanied by
wind splash overwintering bacteria from the residue onto
young plant leaves. This organism does not cause serious
loss.
Gray Leaf Spot (Stage III)
Northern Corn Leaf Blight (Stage II, III)
Gray to tan, rectangular
lesions on leaf, sheath or
husk tissue. Spots are
opaque and long (up to 2
inches). Lower leaves are
affected first, usually not until
after silking. The organism
thrives in extended periods
of warm, overcast days and
high humidity. It has become
more prevalent with increased use of reduced tillage and
continuous corn.
Long (up to 6 inches),
elliptical, gray-green lesions
that become tan-brown
identify infections caused
by this organism. Infection
spreads up the plant
starting on lower leaves. It
is favored by high humidity
and moderate temperatures.
Numerous physiologic races
have been described. Host specific races of the organism
may also attack sorghum.
25
Corn Diagnostic Guide
Phaeosphaeria Leaf Spot (Stage III)
Lesions are initially small,
round to oval, pale green
or yellow, and scattered
on leaves of mature plants.
Spots become light tan with
reddish-brown margins and
may coalesce into irregularly
shaped lesions. This disease
is most prevalent in areas of
high rainfall and moderate
and lower leaf surfaces and readily break through the
epidermis.) This organism is favored by warm, humid
weather.
SMUTTING DISEASES
Common Corn Smut
(Boil Smut, Blister Smut) (Stage I, II, III)
Local infection of any plant
part, even below the soil
surface, occurs through plant
wounds or thin-walled cells
of actively growing tissue.
Resulting galls are first silver-
temperatures.
Physoderma Brown Spot (Stage I, III)
Small yellow spots appear
first at the base of the
leaf. These spots become
brown and combine to form
chocolate-brown to reddish
irregular blotches, sometimes
as bands of infection across
leaf blades. Sheath, husk,
tassel, stalk, and leaves
may exhibit symptoms late
in the season. Infected stalks may break at a node. This
organism is favored by warm, wet weather.
Southern Corn Leaf Blight (Stage II, III)
The most common race,
named “O,” produces small,
elongated (up to 1 inch long),
parallel-sided lesions that are
tan with brownish borders. This
blight primarily attacks leaves. It
is favored by high humidity and
warm temperatures.
Southern Corn Rust (Stage II, III)
Small, circular, orange-tolight-red pustules (blister-like
swelling) occur on leaves,
especially the upper surface,
and sheaths. Pustules rarely
break the leaf surface. (In
contrast, common corn
rust pustules attack upper
white, then become gray
to black powdery masses
of smut spores that are
released when the galls
break open. Galls on leaves
seldom develop beyond
pea-size and tend to harden
and dry without rupturing. High fertility and plant injury
favor the disease. Common smut is not toxic to animals.
Head Smut (Stage III)
Seedling infection results
in systemic development
of the disease as the plant
grows and develops. Tassels
of affected plants may
multiply as a mass of leaves
or be replaced by a black,
smutty mass which ruptures
to release spores, leaving
black, thread-like vascular
strands. Ears may be completely replaced by similar, often
triangular-shaped, smut masses. Occasionally, part of an
ear escapes and produces a few kernels. Hot, dry soil at
seedling stage favors infection. One type of head smut
also attacks sorghum.
26
VIRUS AND VIRUS-LIKE DISEASES
Corn Lethal Necrosis (CLN) (Stage II, III)
Mosaic patterns appear on
leaves and husk. Leaves die
from the margins inward and
plants may die prematurely.
The organism generally starts
at the tassel and works
downward. Barrenness
or sharply reduced grain
production is common. CLN
is caused by synergistic
interaction when plants become infected by maize
chlorotic mottle virus and either maize dwarf mosaic virus
or wheat streak mosaic virus. Presently, the disease has
been identified only in parts of Kansas and Nebraska.
Corn Stunt Spiroplasma (CSS) (Stage II, III)
Corn stunt is caused by a
spiroplasma, not a virus.
Margins of whorl leaf turn
yellow followed by reddening
of older leaves and yellow
striping which runs the
length of leaves. Plants are
stunted, have multiple tillers
and produce numerous small
ear shoots. Root systems
UGA1235014
are reduced. Corn stunt
symptom development and epidemiological patterns are
similar to those of virus diseases.
High Plains Virus (HPV) (Stage I, II, III)
Symptoms begin as small
yellowish flecks which often
appear as lines running
parallel to leaf veins. Infected
seedlings turn bright yellow
and quickly die. Plants may
be stunted, older leaves
may become red and then
necrotic, and ear and kernel
536657
size may be reduced.
Considerable symptom
variation exists among cultivars. It is spread by the wheat
curl mite.
27
Corn Diagnostic Guide
Maize Chlorotic Dwarf Virus
(MCDV) (Stage II, III)
Younger leaves are yellow
and finely striped. There
is a general yellowing
or reddening of leaves
and plants are stunted.
Most affected plants are
barren. MCDV is spread by
leafhoppers from infected
Johnsongrass and other host
species. MCDV is detected
more frequently and is more damaging than maize dwarf
mosaic.
Maize Dwarf Mosaic Virus
(MDMV) (Stage II, III)
Mottling of younger leaves
progresses into narrow, lightgreen to yellowish streaks
along leaf veins. Leaves,
sheaths and husks may show
symptoms. Plants are stunted
and ear size and seed set are
reduced. Sometimes, multiple
tillers or ear shoots develop.
MDMV is most prevalent in
areas where Johnsongrass grows and serves as a winter
host for the virus. It is spread by aphids.
FUNGAL SYSTEMIC DISEASES
Crazy Top (Stage II, III)
Plants have excessive tillering with rolling or twisting of
newer leaves. The tassel
becomes a mass of leaves;
ears, if present, often do
likewise. Leaves are usually
narrow, thick and appear
strap-like. Occasionally oversized plants will develop.
Infection occurs when young
plants are under flooded soil
conditions; therefore, it is
more frequent in low-lying areas. This is one of numerous
downy mildews that attack corn.
Sorghum Downy Mildew (Stage II, III)
Bacterial Stalk Rots (Stage II, III)
At least two organisms have
been identified as causing
bacterial stalk rot. With either,
there is rapid development
of a soft rot of stalks,
accompanied by wilting and
plant death. Stalks twist and
collapse while still green,
disintegrating into a soft
mass often accompanied by
Leaves are yellow with white
stripes; plants are stunted
and ears and tassels multiply
into leafy masses. Often the
base of leaves are chlorotic
and sharply contrast with
healthy green leaf tips. White,
downy growth appears on
either or both leaf surfaces.
Leaves often split or shred.
This is primarily a disease of sorghum.
a foul odor.
STALK AND ROOT ROT DISEASES
Charcoal Rot (Stage III)
Stalk rots are diseases that are most commonly expressed
as plants reach maturity. Stalk rot of corn tends to be a
complex of several disease-causing fungi and sometimes
bacteria; seldom will only one causal organism be isolated
and identified. Plants with rotted stalks almost always have
rotted roots, too. Usually, but not always, the same causal
organisms are involved. Visual identification is very difficult.
Typically, wilting is the first sign of stalk rot in a field. In a
few days, leaves turn a “frosted” gray, ears droop and the
outer rind of the lower stalk turns brown. Fields where
stalk rot is developing should be harvested early to reduce
grain losses.
Anthracnose Stalk Rot (Stage II, III)
Early infection may kill plants
before pollination, but onset
usually occurs just before
plants mature. Sometimes
a portion of the plant above
the ear blanches and dies
prematurely (top dieback).
Usually, the entire plant is
killed and several nodes are
rotted. Late in the season, a
shiny black discoloration develops in blotches or streaks
on the stalk surface, especially on lower internodes.
Internal stalk tissue may become black and soft, starting
at the nodes. Lodging typically occurs higher on the stalk
than with other stalk rots. The same organism causes leaf
blighting earlier in the season.
5361254
Charcoal rot can be
expected when the crop
has grown under hot, dry
conditions; it also attacks
sorghum and soybeans.
Lower internodes are
affected, causing premature
ripening, shredding, and
crown disintegration.
Vascular strands remain
intact but are black or “charred” in appearance. Stalks
become gray-black or charcoal color.
Diplodia (Stenocarpella) Stalk Rot (Stage III)
Lower internodes are
straw-brown, spongy, and
dry. Pith disintegrates,
leaving vascular strands
intact. White fungal growth
may appear on the stalk
surface. Minute, dark bodies
embedded just under the
stalk surface are difficult to
remove.
28
Fusarium Stalk Rot (Stage III)
Rotting of roots, crown, and
lower internodes leads to
premature ripening and stalk
breakage. Split stalks may
show whitish-pink to salmon
color. Disintegration starts at
the nodes.
Healthy stalk, left. Diseased
stalk, right.
Gibberella Stalk Rot (Stage III)
Affected plants wilt, leaves
turn dull gray-green, and
the lower stalk softens and
becomes straw colored
as plants die. Pith tissue
disintegrates, leaving only
vascular strands. The inside
of a rotted stalk is pink to
red. Small, dark bodies are
superficial on the lower stalk
surface and can be scraped off easily.
resulting in darker pigmentation. The role of this root rot in
stalk lodging is not fully understood.
EAR AND KERNEL ROTS
These rots can affect ears, kernels, or cobs, reducing test
weight and grain quality. Some rots are responsible for
development of mycotoxins that may contaminate grain.
Positive identification is difficult. Rotting observed in the
field is often due to a complex of causal organisms, not
just one.
Most ear rots are favored by late-season humidity.
Infections are increased by ear damage by birds or insects
and by stalk lodging that allows ears to come into contact
with the soil.
Aspergillus Ear and Kernel Rot (Stage III)
Greenish or yellowish-tan
discoloration occurs on and
between kernels, especially
near the ear tip. Symptoms
are more prevalent if the husk
does not cover the ear tip.
The rot is favored by hot,
dry weather. It may produce
aflatoxins.
Pythium Stalk Rot (Stage II, III)
This organism attacks individual
plants in localized areas,
sometimes before flowering. It
is usually confined to the first
internode above the soil line,
where rind and pith develop wet
rot. Stalks twist and collapse.
Hot, wet weather favors
development of this stalk rot.
Cladosporium Ear Rot (Stage III)
Dark gray to greenish black
fungal growth causes kernels
to appear blotched or streaked.
Initial discoloration appears
where kernels are attached to
the cob. Infection eventually
progresses upwards and
infected kernels can be seen
Red Root Rot (Stage III)
Red root rot often occurs
in plants that are also
stalk rotted. Seminal roots
are most damaged and
adventitious root damage
increases with their age. The
root color of affected plants
ranges from pink to royal red,
with higher soil temperatures
29
Corn Diagnostic Guide
scattered over the ear. If
completely colonized, ears
are dark and lightweight.
This disease is often
associated with damage due
to insects, hail, or frost.
Diplodia (Stenocarpella) Ear Rot (Stage III)
Penicillium Ear Rot (Stage III)
Symptoms include bleached
husks, white mold over
kernels, and rotted ears with
tightly adhering husks. Early
infection (2 to 4 weeks after
silking) is likely to lead to
complete ear rotting. Later
infections may result in partial
rotting, usually beginning at
the base. Since corn is the
only known host, this disease is most severe when corn is
planted following corn in reduced tillage situations.
Powdery green to bluegreen mold develops on and
between kernels. Infection
usually begins at the ear tips
and primarily occurs on ears
with mechanical or insect
damage. Infected kernels
may become bleached and
streaked. “Blue eye” occurs
when the embryo becomes
discolored due to the presence of blue-green fungal
spores and can occur if infected grain is stored at high
moisture levels.
Fusarium Kernel or Ear Rot (Stage III)
Scattered individual or groups
of kernels show whitish-pink
to lavender fungal growth.
Infected kernels may also
have a “starburst” pattern of
white streaks on the cap of
the kernel or along the base.
Infections are more frequent
on damaged ear tips, and
are favored by dry weather.
Fusarium rot may produce mycotoxins.
Gibberella Ear Rot (Stage III)
Symptoms include reddish
kernel discoloration, usually
beginning at the ear tip.
Husks may rot and be
cemented to the ear. The
organism is favored by cool,
humid weather, particularly
2 to 3 weeks after silking. It
produces several mycotoxins.
Trichoderma Ear Rot (Stage III)
Dark green fungal growth
is found on and between
kernels and husks, often
covering the entire ear. The
disease usually occurs on
ears with mechanical or insect
damage. Infected plants tend
to be widely distributed within
a field.
Photo Citations:
Clemson University - USDA Cooperative Extension Slide
Series, Bugwood.org (viewed 9/22/10); Corn Stunt
1235014
William M. Brown Jr., Bugwood.org (viewed 9//22/10)
High Plains Virus 5366657
Howard F. Schwartz, Colorado State University, Bugwood.
org (viewed 9/22/10) Bacterial Stalk Rot 5361254
Holcus spot and Pythium stalk rot photos courtesy of Don
White at University of Illinois
30
6
Insect Identification, Injury
Symptoms, & Management
Recommendations
Only the most common or the most economically –damaging corn insects in the North American region are
discussed in this chapter. Most, but not all, insect identifications can be made in the field by trained individuals.
As insects progress through their life cycles, they change form and features. The following comments
describe the appearance of damaging stages, which may not correspond with their appearance when damage
is being investigated. It is not uncommon to investigate crop insect damage, but find none of the suspected
insects. At other times, damage from insect feeding may be detected, but the insect is no longer present.
Use economic thresholds whenever possible and seek further pest management guidance if symptoms are
unclear. Generalized thresholds for most pests are provided in this guide. These thresholds may change
depending on the cost of a control tactic or the commodity value. Always confirm that pest numbers have
been suppressed below thresholds following the application of a rescue tactic. Pesticides may perform below
expectation due to environmental, chemical, or biological situations, or due to application timing.
While this publication is focused on in-season diagnostics and treatment options of insect pests of corn, a
number of Bt traits are available for several of the insect pests discussed in this handbook. The Corn Insect
Control with Monsanto Corn Insect Traits and Seed Treatments table (see pp. 39) provides a list of some of
these products as well as the insects they control. These products provide season-long control of the specific
insects and reduce the need for additional pest management action.
APHIDS
(1) Corn Leaf Aphid
This small, soft-bodied,
bluish-green to gray insect
colonizes on or in the
whorl, upper leaves, and
tassel, especially under
dry conditions. It sucks
plant juices and can cause
wilting, pollen shed failure,
and barrenness. The aphid
secretes a sticky honeydew
that may gather dirt and act as a medium for mold.
Predatory insects, like the lady beetle, may be present
and are important predators of aphids. Scouting should
31
Corn Diagnostic Guide
occur during late whorl to early tassel. Aphid infestations
after 50% pollen shed have little effect on grain yield. A
rescue application of insecticide may be warranted if 50%
or more plants have light to moderate infestations and the
crop is under moisture stress.
(2) Corn Root Aphid
This pinhead-sized, soft-bodied, blue-green to gray-green
insect, may be winged or wingless. Corn root aphid groups
are found in clusters on the crown and along the roots of
young plants. They suck plant juices and cause wilting,
discoloration, and stunting. Cornfield ants are generally found
in conjunction with corn root aphid colonies. There are no
rescue treatments for corn root aphid. Cultural practices like
crop rotation and tillage can be effective preventative tactics.
ARMYWORMS
Fall Armyworm
The fall armyworm grows
up to 1.5 inches long and
appears greenish-brown in
color with an inverted white
“Y” on its head. It chews
ragged holes in the leaves
and usually concentrates in
the whorl of young plants.
The fall armyworm also feeds on the tassel and bores into
developing ears. Early detection is critical since this pest
feeds in protected areas of the plant. It lays round, gray
eggs in clusters of 50 or more, which are usually covered
with scales. Eggs hatch in 3 to 5 days and larvae migrate
to the whorl and adjacent plants. Consider using a rescue
application if eggs are present on at least 5% of plants or
whorl injury is detected on 25% or more plants. Because
larvae feed deep in the whorl of young plants, control with
insecticides can be difficult.
(2) True Armyworm
The true armyworm is
greenish-gray with orange
or pinkish lines along the
body. “Armies” migrate from
maturing small grains or
grass at night. They devour
foliage, sometimes leaving
5364223
only leaf midveins, and chew
silks. Infestations are more frequent in no-till or reduced
tillage systems and the true armyworm is usually only an
occasional pest in rotated corn. Consider an insecticide
application if 35% or more plants in the field are infested.
BILLBUG
UGA1234011
This black or gray hardshelled snout beetle is active
only at night. Leaves are
punctured while still rolled in
the whorl. When they unfurl,
irregular rows of holes appear
across the leaves. The billbug
also chews into plant stems
at or below ground level.
This feeding can damage
the growing point and cause plants to be bent, twisted
or stunted and sometimes die. Billbug incidence is often
associated with nutsedge. Consider spraying for billbug if
stand loss during seedling stages exceeds 5%.
CEREAL LEAF BEETLE
The adult is a 0.2 inch long, hard-shelled beetle with
metallic blue-black head and wing covers, and reddishorange legs and thorax. Feeding on corn is rare and
usually limited to field borders. Though the beetle eats
completely through the leaf between the veins, plants
normally outgrow the injury and rescue applications
are not necessary. Generally infestations are limited to
Michigan, Indiana, and eastward.
CHINCH BUG
The adult is 0.25 inch long,
and is red and black with
white wing covers. When
crushed, this bug emits a
distinct odor. It migrates
from grasses and maturing
small grains, attacks field
borders first and is most
destructive during dry years.
The young nymph (juvenile
stage) is bright red, but turns black as it develops. Chinch
bugs cluster in groups behind the sheath of lower leaves,
sucking plant juices and causing wilting and eventual
plant death. Management may be necessary if 10 or
more chinch bugs are found on more than 50% of plants.
Insecticide applications may be limited to only the infested
area.
COMMON STALK BORER
This purplish-brown larva may
reach 2 inches in length. It
has white longitudinal stripes
with a distinct purple saddle
near the middle of the body. It
tends to move out of weedy
or grassy field borders and
attack corn on field edges (or
throughout no-till fields). The
larva tunnels into stalks or
whorls. Infestation of plants at the 4-7 leaf stage can lead
32
to dead heart. Whorl feeding results in leaves that have
a ragged appearance with injury appearing as a series of
holes across the leaf. Timing insecticide applications prior
to borer tunneling is critical. Consider treating if 10% of
V2 plants, 15% of V4 plants, or 30% of V6 plants show
symptoms.
CORN BORER
(1) European Corn Borer
This larvae varies in shades
of tannish-gray and ranges
in size from less than 0.5 to
1.0 inch long. There are two
and prepare overwintering
tunnels in the stalk below
soil level. These larvae girdle
the plants near the soil level,
resulting in severe stalk
lodging. Treatment may be
necessary for first generation
populations when greater than
35% of plants hold larvae or
show symptoms. Insecticide
applications for both first and second generations must
be applied before they begin tunneling. Consider a rescue
treatment for second generation if eggs or young larvae are
found on 20 to 25% of plants.
CORN EARWORM
or more generations per
season. Larvae of the first
generation feed on leaves
before they burrow into the
stalk. This feeding causes broken midribs and creates a
“shot hole” appearance as leaves grow out of the whorl.
Consider treating first generation populations if the moth
flight has already peaked and 5% or more of plants have
shot hole feeding. Second generation larvae feed on and
bore into stalks, tassels, ear shanks, and ear tips causing
top breakage, ear drop (with husk attached), stalk lodging,
and kernel damage. Treatment for second generation
larvae may be necessary if more than 10% of plants have
fresh or hatched egg masses, or young larvae in the
leaf axils. Timing insecticide applications prior to insect
tunneling is critical.
(2) Southwestern Corn Borer
This larvae is white or cream-colored and 0.5 to 1.0
inch long. It has distinct black spots except on the
overwintering form. Two generations feed on corn. The
first feeds on leaves and creates a “shot hole” effect
or “dead heart” in very young plants. Later instars
tunnel in the stalk. The second generation larvae feed
on developing ear tissue, bore into the shank and ear,
and tunnel in the stalk below the ear zone. In the fall,
overwintering larvae migrate to the base of the stalk
33
Corn Diagnostic Guide
This larva varies in color from green, yellow, brown to
pink, but all have a yellow-brown head and reach full size
at about 1.5 inches. Since
the insect is cannibalistic,
two or more full-size larvae
are seldom found together.
They may feed on leaves in
the whorl, on
the tassel or
on silks, but
the preferred feeding
site is ear tips and on
developing kernels.
Moreover, ear injury
often leads to ear
molds and rots. The
window for effective
treatment is the few
days after eggs are laid and before larvae tunnel into the
silk channel.
CORN ROOTWORM
This small, white larva feeds on and tunnels into roots
or crowns of young plants. It destroys root systems,
can delay development, and causes root lodging.
Lodging is accentuated by wind storms. Plants may
“gooseneck” across rows and resume upright growth.
Rescue treatments for control of corn rootworm larvae
are available, but efficacy
is greatly dependent on the
product’s ability to move into
the root zone. Continuous
corn or observations of adult
beetles made the previous
year can trigger the use of
control tactics. The adult
beetle may feed on corn
leaves, stripping spots of
the upper surface away. After pollen shed, it feeds on
pollen and fresh silks. Heavy silk feeding can reduce or
prevent pollination and result in partial or complete failure of
(2) Northern Corn Rootworm
The adult beetle is less than
0.5 inch long, tan or green
to greenish-yellow without
distinctive spots or stripes.
(3) Southern Corn Rootworm
The adult beetle is 0.25 to 0.5
inch long, yellow or greenish
with six black spots on each
wing cover.
(4) Western Corn
Rootworm
Corn rootworm feeding
The adult beetle is about
0.25 inch long, black and
kernel set. The beetle can be found in ear tips as maturity
approaches. The general guideline for silk clipping insects
is as follows: control may be necessary if silks are clipped
to less than 0.5 inch and fewer than 50% of plants have
been pollinated. Also, one beetle per plant in late summer
is a useful guideline for justifying whether a control tactic
may be necessary to prevent larval injury in continuous
corn.
(1) Mexican Corn
Rootworm
The adult beetle is light
green and looks similar
to the northern corn
rootworm beetle, but can
be distinguished by a black
stripe on the leg.
yellow striped or black
with a yellow tip on the
wing cover. It cannot
be visually identified as
to species.
CUTWORM
There are many species of cutworms that attack corn
and other crops such as cotton, tobacco, and many
vegetable crops. Cutworms are widely distributed; some
species migrate to Corn Belt states from the South and
many overwinter there. Young larvae typically feed on leaf
margins and larger larvae feed below or at the soil surface.
They chew into or completely cut young stalks, causing
34
wilting or death. Plants may recover if injury is limited to
above the growing point. Cutworms are primarily active at
night. An insecticide application should be considered if 2
to 3% of seedling plants are wilted or cut and larvae are
early in their development (<0.75 inch). If larvae are larger,
increase the economic threshold to 5% of plants wilted or
cut. Plants at V5 or later stages of development usually are
unaffected by cutworms.
(1) Black Cutworm
The black cutworm larva
varies from almost black to
lighter gray and is a pest of
many crops at the seedling
stage. Most of the Corn Belt
is re-colonized each year
with migrant adults. Cutting
is usually observed 300
degree days (base 50°F) after
heavy adult activity. Several
generations per year are possible, but the first generation
in spring is most injurious. Areas of high soil moisture or
low-lying areas within a field are most favorable for this
insect and should be scouted first.
(3) Other Cutworms
The bronzed, claybacked, dingy, glassy, sandhill, and
variegated cutworms are less frequent pests and less
injurious to corn.
FLEA BEETLE
The flea beetle is a tiny, shiny,
black beetle that jumps like a
grasshopper when disturbed.
It feeds on leaves of young
plants and produces “scratch
marks” or small holes. The
flea beetle is the primary
vector of the bacterium that
causes bacterial (Stewart’s)
wilt of corn. Consider treating
field corn if five or more beetles per plant are found on
V4 or younger corn and adverse growing conditions have
slowed corn growth. Current seed treatments generally
provide good control.
GRAPE COLASPIS This white, curved, grub-like
larva develops six distinct
foreleg projections. It feeds
on young corn roots and can
cause nutrient deficiency
symptoms.
(2) Western Bean Cutworm
The western bean cutworm
affects corn during
reproductive stages. The
young larva has a pale body
with longitudinal brown stripes
along the back. Fully grown, it
is light brown to pale gray with
a brown head. The cutworm
feeds on silks and chews into
husks and developing ear
tips of the ear shank. Severe
ear and kernel damage can
lead to mold and ear rots.
This insect has historically
been limited to the western
Great Plains, but has moved eastward and can now be
found in many areas of the Corn Belt.
35
Corn Diagnostic Guide
GRASSHOPPER
Several species of
grasshoppers attack corn.
The grasshopper generally
moves from field-side
hatching sites. It eats
leaves from the margin
inward and may prevent
pollination by clipping silks. The grasshopper may also
chew on tassels, husks, stalks, or kernels. Defoliation and
ear damage should be used to determine if an insecticide
treatment is necessary in field corn. It may be more
economical to limit applications to infested areas like field
margins.
UGA4709020
JAPANESE BEETLE
This shiny, green-bodied
adult beetle has copper- to
bronze- colored wing covers.
As an adult, it grows to about
0.5 inch in length and feeds
on corn leaves and silks. Leaf
feeding by this pest appears
skeletonized or “lacy.” Larvae
are white with a brown head
and feed unobtrusively on
the roots of plants. They can be differentiated from other
white grubs by the V-shaped pattern of bristles on the
raster. The general guideline for silk clipping insects, such
as an adult Japanese beetle, is as follows: control may
be necessary if silks are clipped to less than 0.5 inch and
fewer than 50% of plants have been pollinated.
LEAF MINER
This small, white larva or
maggot tunnels between leaf
surfaces, leaving long blotchy
tunnels within the leaf. This
pest seldom reaches economic
proportion in corn.
cream colored spots on wing covers. It frequently inhabits
ear tips as corn approaches maturity and often appears
where primary insect pests or birds have damaged ear tips.
SEED CORN BEETLE
This small, 0.25 to 0.33 inch long brown ground beetle
damages the germ and hollows seed before it germinates.
The beetle also attacks emerging seedlings, causing spotty
stands. Damage is greatest if germination has been delayed
by the environment. Current seed treatments generally
provide good control.
SEED CORN MAGGOT
This yellowish-white spindleshaped larva, is about 0.25
inch long and may eat
the entire kernel before it
germinates. Often times it
leaves only the seed coat
behind. Wet, cold, and heavy
soils are associated with this
pest that can create spotty,
uneven stands. Modern seed
treatment provides good control. Otherwise, there is no rescue
treatment for seed corn maggot and replanting may be the
only option.
SLUG
LESSER CORNSTALK BORER
This black larva with white
bands burrows into the stalk
base of young plants. This
borer causes wilting and plant
deformities like twisted, bent
or often barren plants.
UGA2511032
PICNIC BEETLE
(Sap Beetle,
Scavenger Beetle)
(to right)
This small, dark beetle
usually has four orange or
This soft-bodied, slimy and
legless grayish creature
hides under residue. It is
active at night and leaves a
telltale silver-colored slime
trail on the soil surface. It
feeds using a rasping action
on the lower stalk and leaves
of young plants. This feeding
often removes only one
surface of a leaf and the symptom is more common in notill systems. Insecticidal baits are available for slug control,
however, injury seldom warrants this expense.
SOUTHERN CORN LEAF BEETLE
Adult beetles are dark brown and can be difficult to find in
the field because they are often covered with soil. Beetles
feed on stems and on the edges of leaves of seedlings.
Injured plants appear ragged. When beetles feed in large
36
numbers, plants may die. This beetle is most problematic
in fields that have not been cultivated.
reduced ear weight. The sugarcane borer is found in
Florida, Louisiana, Mississippi, and Texas.
SPIDER MITE
THRIPS
Two species can cause
severe damage to corn:
banks grass mite and twospotted spider mite. Spider
mite problems are more
prevalent when temperatures
are high and humidity and
rainfall are low. The tiny (about
the size of a pencil dot), eightlegged creature feeds by
piercing individual leaf cells and sucking out the contents.
Damage is usually first noted as plants approach tasseling
and continues through grain dent stage. Lower leaves
appear blotched and chlorotic and continued feeding can
cause leaves to die. Damage symptoms progress up the
plant with time. The mite spins a white web on the leaf
surface where it feeds.
STINK BUG
Several species of green or
brown stink bugs occasionally
attack corn. The adult (shield
bug) has a hard, angular back
and wing covers, and gives
off a foul odor if crushed. It
inserts its piercing-sucking
mouthparts into the base
of young plants and can kill
the growing point or distort
further growth.
SUGARCANE BORER
This tan larvae has
indistinct brown spots on
each segment. It feeds in
whorl-and reproductivestage plants similar to
the southwestern corn
borer, except that it does
not girdle the stalk. Yield
losses occur due to
37
Corn Diagnostic Guide
Several species of this tiny, slender insect occasionally
feed on leaves of young corn plants. As an adult, it
develops wings. With mouthparts fitted for rasping and
sucking, thrips remove the green surface layer in tiny
streaks. Individual leaves have a speckled appearance and
fields, or affected areas, may look silvery.
WEBWORM
The garden webworm and sod webworm attack young
corn. It appears as a gray to yellow-green, spotted, bristly
larva about 1 inch long. This pest gets its name from the
fine web it spins from its silk-lined underground nest. The
larva uses this web to travel to plants at night and return
to its nest during the day. Similar to the cutworm and
wireworm, the webworm’s primary feeding site is at or
just below the surface. Injury becomes more obvious as
damaged leaves emerge from the whorl. Larvae also feed
on the underside of lower leaves.
WHEAT CURL MITE
(Kernel Red Streak)
Kernel red streak is caused
by a toxin secreted during
feeding of the wheat curl
mite. It is most common on
yellow corn, but may occur
on sweet corn, popcorn,
and white corn. Streaks are
more pronounced toward ear
tips, especially if kernels are
exposed. Streaks vary from
dark red on yellow kernels to pink on white kernels. No
detrimental effects from the discoloration are known.
WHITE GRUB
The larva has a thick,
soft body with three
pairs of legs just behind
a brown head. It ranges
from 0.125 to 1.5 inches
long depending on
age, and it characteristically curls into a “C”-shape when
disturbed. There are several species with 1 to 4 year life
cycles. The white grub feeds on developing roots of young
plants, and causes stunting, nutrient deficiency symptoms
and death. Heaviest infestations occur where corn is
planted into killed sod. There are no rescue treatments
for grubs and the percent stand loss is the best gauge for
determining if replanting is worthwhile.
WIREWORM
The larva is shiny and slender
with a yellow- to browncolored hard body. It ranges
in size from 0.5 to 1.5 inches
long, depending on age and
species. Damage to seed or
young plants reduces stand
and vigor. It damages the
germ, stunts plants by root
pruning or kills the growing
point by boring into the base of the stem near ground
level. Modern seed treatments prevent damage to seeds.
Like grubs, there is no way to combat this pest after
stands have been thinned. Use percent stand loss as a
gauge for determining if replanting is worthwhile.
Photo Citations:
Frank Peairs, Colorado State University, Bugwood.org (viewed
9/23/10) Armyworm 5364223
Clemson University - USDA Cooperative Extension Slide Series,
Bugwood.org (viewed 9/23/10) Billbug 1234011
University of Georgia Archive, University of Georgia, Bugwood.
org (viewed 3/11/2011) Grasshopper 4709020
David Riley, University of Georgia, Bugwood.org (viewed
9/23/10) Lesser Cornstalk Borer 2511032
Alton N. Sparks, Jr., University of Georgia, Bugwood.org (viewed
3/11/2011) White grub (scarab) 1327103
Corn earworm damage
38
Corn Insect Control with Monsanto Corn Insect Traits
and Seed Treatments
Protection for Above and Below Ground Pests
Genuity®
SmartStax®
Trait Name
Genuity® VT
Triple PRO™
YieldGard VT
Triple®
Protection for
Above Ground
Pests
Genuity® VT
Double PRO™
Trait Logo
Poncho® 250
Seed Treatment
Below Ground
Above Ground
Insects
European corn borer
Trait
Trait
Trait
Trait
Southwestern corn borer
Trait
Trait
Trait
Trait
Corn earworm (ear feeding)
Trait
Trait
Trait
Trait
Western bean cutworm
Trait
NC
NC
NC
Black cutworm
Trait/250 Rate
250 Rate
250 Rate
250 Rate
Fall armyworm
Trait
Trait
Trait
Trait
Sugarcane borer
Trait
Trait
Trait
Trait
Common stalk borer
Trait
Trait
Trait
Trait
Lesser cornstalk borer
Trait
Trait
Trait
Trait
Corn flea beetle (seedling stage)
250 Rate
250 Rate
250 Rate
250 Rate
Corn leaf aphid (seedling stage)
250 Rate
250 Rate
250 Rate
250 Rate
Chinch bugs (seedling stage)
250 Rate
250 Rate
250 Rate
250 Rate
Southern corn leaf beetle
(seedling stage)
250 Rate
250 Rate
250 Rate
250 Rate
Western corn rootworm larvae
Trait
Trait
Trait
NC
Northern corn rootworm larvae
Trait
Trait
Trait
NC
Mexican corn rootworm larvae
Trait
Trait
Trait
NC
Wireworm (seedling stage)
250 Rate
250 Rate
250 Rate
250 Rate
White grubs (seedling stage)
250 Rate
250 Rate
250 Rate
250 Rate
Grape colaspis (seedling stage)
250 Rate
250 Rate
250 Rate
250 Rate
Seedcorn maggot (seedling stage)
250 Rate
250 Rate
250 Rate
250 Rate
Color Key to Activity
Insect activity conferred by:
= Control
Trait, Insecticide 250 rate, or multiple
= Suppression
Trait, Insecticide 250 rate, or multiple
= No Control
NC = No Control
39
Corn Diagnostic Guide
7
Herbicide Injury
Symptoms
Most observed herbicide damage is due to misapplication, but hybrid and environment interactions will
sometimes cause injury symptoms to appear. Herbicides used to control weeds in the previous crop must be
taken into consideration, as some herbicide carryover may affect the following corn crop.
Various tankmixes of herbicides are widely used. Be alert to plant injury that can be caused by individual
tankmix components or by an interaction involving two or more components in the tankmix itself.
Corn plants frequently outgrow the effects of herbicide injury and their final yields may not be noticeably
lowered.
ACCase Inhibitors
Aryloxyphenoxy Propionic Acids and
Cyclohexanediones
(Including Assure® II, Fusion®, Poast® and Select Max®)
Symptoms of damage from
acetyl coA carboxylase
inhibitors include chlorosis
(yellowing) of newly formed
leaves with possible
reddening or purpling of
older leaves. Tissues at the
growing point turn brown
and eventually decompose,
a symptom called deadheart.
Sublethal doses result in pale white to yellow streaks
between leaf veins.
ALS Inhibitors
Imidazolinones, Sulfonylureas, and
Triazolopyrimidines
(Including Accent Gold®, Beacon®, Classic®, FirstRate®,
Lightning®, Pursuit®, and Scepter®)
These herbicides alter the
function of the acetolactate
synthase (ALS) enzyme and
affect root and shoot growth
and development. Corn
injury typically shows up as
reduced root systems, often
described as “bottle-brush”
roots. Roots often grow flat
or parallel to the soil surface
and may turn brown. Stems and
midribs can purple, and the stem will be
short and thick below the whorl. Mid–
to late-season symptoms include short
internodes, malformed leaves, poor root
systems, and pinched ears.
Herbicides with sulfonylurea chemistry
are labeled for use on both corn and
soybeans. Products in this family may
persist in the soil, particularly if soil
pH is above 6.8 and post-application
rainfall has been limited. Though
they have the same general chemistry,
different herbicides are used on corn
and soybeans, and injury of corn
may develop the season following
sulfonylurea herbicide application to
soybean fields.
40
Synthetic Auxins
Cell Division Inhibitors
Benzoic Acids, Phenoxys, and Pyridine
Carboxylic Acids
Amides
(Including Banvel , Butyrac , Clarity , and Crossbow )
These herbicides, also
known as plant growth
regulators, are translocated
to meristematic tissue and
interfere with cell formation
resulting in abnormal root and
shoot growth. Symptoms
®
®
®
®
include twisted whorls or
buggy-whipping where
the leaves do not unfurl,
abnormal brace roots,
root proliferation, brittle
stalks, and poor pollination.
Growing conditions
are a factor in damage
expression.
Auxin Transport Inhibitors
(Including Degree®, Dual II Magnum®, and Harness®)
Amides (also known as
acetanilides, acetamides,
or chloroacetamides) are
meristematic growth inhibitors
that are translocated to the
shoot and leaves. These
products can cause seedlings
to leaf underground or trap
seedling leaves so they
cannot unfurl, giving a ladder
effect. Damage is more likely to take place with cool, wet
weather occurring immediately before emergence.
EPSP Synthase Inhibitors
Glycines
(Including Roundup® agricultural herbicides and
generic formulations of glyphosate)
These non-selective foliarapplied herbicides are
translocated and interfere
with amino acid synthesis.
Semicarbazones
(Including Distinct®and Status®)
These herbicides are primarily active against broadleaf
plants, but injury symptoms may occur in corn under
certain conditions. Injury is similar to growth regulator
herbicides.
Carotenoid Synthesis Inhibitors
Isoxazolidinones
(Including Command®)
Shallow planting or stress
conditions that slow seedling
metabolism can increase the
potential for injury. Damage
to corn seedlings the season
following an application may
occur, especially if soil pH is
below 6.0. Affected plants are
distinctly white or bleached.
Most corn plants recover and
new leaves have normal color.
41
Corn Diagnostic Guide
If spray drift reaches corn,
leaves wilt, turn brown,
and die. Sublethal rates
can cause phenoxy-like
symptoms. Glyphosate applications that occur too late to
corn with Roundup Ready® 2 Technology can result in poor
kernel set.
Glutamine Synthase
Inhibitors
Phosphinic Acids
(Including Ignite® and Liberty®)
Inhibitors of glutamine synthase
are nonspecific and will kill
plants that have not been
modified to express resistance
to them. Symptomology will
range from light speckling on leaves and yellowing to
plant death, depending on the degree and intensity of drift
or spray contamination.
4-HPPD Inhibitors
Isoxazoles and Triketones
(Including Balance®, Balance® Pro, Callisto®, and Impact®)
Injury symptoms
range from minor
yellowing, through
completely bleached
plants, to significant
stand loss. Shallow
planting or stress
conditions that slow seedling
metabolism can increase
the potential for injury. New
tissue development should
not be affected and the effect
of injury on yield potential will
vary from field to field.
Microtubule Inhibitors
Dinitroanilines
(Including Prowl® and Treflan®)
Dinitroanilines function by
inhibiting root and shoot
growth. Injury can occur
due to carryover from an
application made the previous
season. Seedling roots
are pruned and clubbed.
Stunting and purplish
discoloration may occur
above ground. Symptoms
may be confused with nematode damage.
PPO Inhibitors
Diphenyl Ethers,
Phenylphthalimides,
Pyrimidines, and
Triazolinones
(Including Aim®, Authority®,
FlexStar®, Reflex®, and
Resource®)
Herbicide application during
hot, humid conditions or before
a long period of cool weather can result in crop injury. Drift
injury can occur if application takes place under windy
conditions. Symptoms range from leaf speckling to
browning and death of entire leaves. If enough plant tissue is
affected, the plant may wilt and die.
The season following application in soybeans, nondegraded herbicide residue can cause interveinal
bleaching and discoloration of corn seedlings if postapplication rainfall was unusually low.
Photosystem I Electron Diversion
Bipyridiliums
(Including Gramoxone Inteon™)
Drift of these non-selective contact herbicides may cause
leaf spotting. Symptoms can be confused with disease;
however, the dead leaf areas will not spread.
Photosystem II Inhibitors—mobile
within plant
Triazines and Ureas
(Including atrazine, AAtrex®, Princep®, Sencor®
and Lorox®)
These chemical families inhibit photosynthesis, which leads
to leaf yellowing, browning, and death, usually starting at
the leaf margins and tip. New leaves may be symptomfree. Symptoms are more common on sandy soil where an
excessive rate was applied. Unfavorable growing conditions
may accentuate plant injury.
Photosystem II Inhibitors—nonmobile
within plant
Benzothiadiazoles and Nitriles
(Including Basagran®and Buctril®)
These are contact herbicides that are absorbed through
the foliage. Leaf speckling after foliar application is a
common injury symptom.
42
Herbicides that may be used or trigger symptomology in
corn, grouped by mode of action and class of chemistry.
HERBICIDE MODES OF ACTION
Acetyl CoA Carboxylase Inhibitors
Assure II
Fusilade® DX
Fusion®
®
Hoelon®
Poast
Poast Plus®
Select®
Select MAX®
ACCase Inhibitor
ACCase Inhibitor
ACCase Inhibitor
ACCase Inhibitor
Acetolactate Synthase Inhibitors
Authority
Assist
Optill™
Lightning®
Pursuit®
Pursuit® Plus
Raptor®
Scepter®
Squadron®
Steel®
®
Accent
Accent Gold®
E.I. du Pont de Nemours & Co.
Syngenta
Syngenta
Bayer
Cyclohexanediones
Cyclohexanedione
Cyclohexanedione
Cyclohexanedione
Cyclohexanedione
BASF
BASF
Valent USA Corporation
Valent USA Corporation
Imidazolinones
ALS Inhibitor + PPO Inhibitor
Imidazolinone + Triazolinone
FMC Corporation
ALS Inhibitor + PPO Inhibitor
ALS Inhibitor + ALS Inhibitor
ALS Inhibitor
ALS Inhibitor + Microtubule Inhibitor
ALS Inhibitor
ALS Inhibitor
ALS Inhibitor + Microtubule Inhibitor
ALS Inhibitor + ALS Inhibitor +
Microtubule Inhibitor
Imidazolinone + Pyrimidinedione
Imidazolinone + Imidazolinone
Imidazolinone
Imidazolinone + Dinitroaniline
Imidazolinone
Imidazolinone
Imidazolinone + Dinitroaniline
Imidazolinone + Imidazolinone +
Dinitroaniline
BASF
BASF
BASF
BASF
BASF
BASF
BASF
BASF
Acetolactate Synthase Inhibitors
®
TRADEMARK OWNER
Aryloxphenoxypropionates
ACCase Inhibitor
Aryloxyphenoxypropionate
ACCase Inhibitor
Aryloxyphenoxypropionate
ACCase Inhibitor + ACCase Inhibitor Aryloxyphenoxypropionate +
Aryloxyphenoxypropionate
Aryloxyphenoxypropionate
ACCase Inhibitor
Acetyl CoA Carboxylase Inhibitors
®
CLASS OF CHEMISTRY
ALS Inhibitor
ALS Inhibitor + ALS Inhibitor +
Authority® XL
Beacon®
Canopy®
Celebrity® Plus
ALS Inhibitor + PPO Inhibitor
ALS Inhibitor + Auxin
ALS Inhibitor
ALS Inhibitor + PPO Inhibitor
ALS Inhibitor + Auxin + Auxin
Transport Inhibitor
Classic®
ALS Inhibitor
Exceed®
ALS Inhibitor + ALS Inhibitor
NorthStar®
ALS Inhibitor
Option®
ALS Inhibitor + Auxin
Peak®
ALS Inhibitor
Permit®
ALS Inhibitor + 4-HPPD Inhibitor
Realm™ Q
ALS Inhibitor + ALS Inhibitor
Resolve® Q
ALS Inhibitor + ALS Inhibitor
Spirit®
ALS Inhibitor + ALS Inhibitor
Steadfast®
Steadfast® ATZ ALS Inhibitor + ALS Inhibitor + PS II
Inhibitor
Synchrony® XP ALS Inhibitor + ALS Inhibitor
PPO Inhibitor + ALS Inhibitorr
Valor® XLT
ALS Inhibitor + Auxin
Yukon®
Sulfonylureas
Sulfonylurea
Sulfonylurea + Sulfonylurea +
Triazolopyrimidine + Pyridine
Sulfonylurea + Triazolinone
Sulfonylurea
Sulfonylurea + Triazine
Sulfonylurea + Benzoic Acid +
Semicarbazone
Sulfonylurea
Sulfonylurea + Sulfonylurea
Sulfonylurea + Benzoic Acid
Sulfonylurea
Sulfonylurea
Sulfonylurea
Sulfonylurea + Triketone
Sulfonylurea + Sulfonylurea
Sulfonylurea + Sulfonylurea
Sulfonylurea + Sulfonylurea
Sulfonylurea + Sulfonylurea + Triazine
E.I. du Pont de Nemours & Co.
E.I. du Pont de Nemours & Co.
Sulfonylurea + Sulfonylurea
Phenylphthalimide + Sulfonylurea
Benzoic Acid + Sulfonylurea
E.I. du Pont de Nemours & Co.
Valent USA Corporation
Nissan Chemical Industries, Ltd.
FMC Corporation
Syngenta
E.I. du Pont de Nemours & Co.
BASF
E.I. du Pont de Nemours & Co.
Syngenta
Syngenta
Bayer
Syngenta
Nissan Chemical Industries, Ltd
E.I. du Pont de Nemours & Co.
E.I. du Pont de Nemours & Co.
Syngenta
E.I. du Pont de Nemours & Co.
E.I. du Pont de Nemours & Co.
Herbicides shown in bold type contain two or more active ingredients, so they may appear in more than one section of the table.
43
Corn Diagnostic Guide
HERBICIDE MODES OF ACTION
Acetolactate Synthase Inhibitors
Accent Gold®
ALS Inhibitor + ALS Inhibitor + ALS
Inhibitor + Auxin
Authority™ First ALS Inhibitor + PPO Inhibitor
ALS Inhibitor
Broadstrike™
ALS Inhibitor
FirstRate®
ALS Inhibitor + PPO Inhibitor
Gangster®
Gauntlet®
Hornet®
Python®
SureStart™
ALS Inhibitor + PPO Inhibitor
ALS Inhibitor + Auxin
ALS Inhibitor
ALS Inhibitor + Auxin + Cell Division
Inhibitor
Cell Division Inhibitor + Auxin + ALS
Inhibitor
TripleFLEX™
Herbicide
Synthetic Auxins
Banvel®
Celebrity® Plus
Clarity®
Distinct®
Marksman®
NorthStar®
Status®
Yukon®
Auxin
ALS Inhibitor + Auxin + Auxin
Transport Inhibitor
Auxin
Auxin + Auxin Transport Inhibitor
Auxin + PS II Inhibitor
ALS Inhibitor + Auxin
Auxin + Auxin + Transport Inhibitor
ALS Inhibitor + Auxin
Synthetic Auxins
2,4-D
Butyrac®
Crossbow®
Auxin
Auxin
Auxin + Auxin
Synthetic Auxins
Accent Gold
®
Crossbow®
Hornet®
Stinger®
SureStart™
Tordon®
Transline®
TripleFLEX™
Herbicide
WideMatch®
ALS Inhibitor + ALS Inhibitor +
ALS Inhibitor + Auxin
Auxin + Auxin
ALS Inhibitor + Auxin
Auxin
ALS Inhibitor + Auxin + Cell Division
Inhibitor
Auxin
Auxin
Cell Division Inhibitor + Auxin + ALS
Inhibitor
Auxin + Auxin
Auxin Transport Inhibitors
Celebrity® Plus
Distinct®
Status®
ALS Inhibitor + Auxin + Auxin
Transport Inhibitor
Auxin + Auxin Transport Inhibitor
Auxin + Auxin + Transport Inhibitor
CLASS OF CHEMISTRY
TRADEMARK OWNER
Triazolopyrimidines
Pyridine + Sulfonylurea +
Sulfonylurea + Triazolopyrimidine
Triazolopyrimidine + Triazolinone
Triazolopyrimidine
Triazolopyrimidine
Triazolopyrimidine +
Phenylphthalimide
Triazolopyrimidine
Triazolopyrimidine + Triazolinone
Triazolopyrimidine + Pyridine
Triazolopyrimidine
Triazolopyrimidine + Pyridine +
Amide + Pyridine +
Triazolopyrimidine
E.I. du Pont de Nemours & Co.
FMC Corporation
Dow AgroSciences LLC
Dow AgroSciences LLC
Valent USA Corporation
FMC Corporation
Dow AgroSciences LLC
Dow AgroSciences LLC
Dow AgroSciences LLC
Monsanto Technology LLC
Benzoic Acids
Benzoic Acid
Sulfonylurea + Benzoic Acid +
Semicarbazone
Benzoic Acid
Benzoic Acid + Semicarbazone
Benzoic Acid + Triazine
Sulfonylurea + Benzoic Acid
Benzoic Acid + Semicarbazone
Benzoic Acid + Sulfonylurea
BASF
BASF
BASF
BASF
BASF
Syngenta
BASF
Nissan Chemical Industries, Ltd.
Phenoxy Carboxylic Acids
Phenoxy
Phenoxy
Phenoxy + Pyridine
Generic chemical name
Allbaugh, Inc.
Dow AgroSciences LLC
Pyridine Carboxylic Acids
Pyridine + Sulfonylurea +
Sulfonylurea + Triazolopyrimidine
Phenoxy + Pyridine
Triazolopyrimidine + Pyridine
Pyridine
Triazolopyrimidine + Pyridine +
Amide
Pyridine
Pyridine
Amide + Pyridine +
Triazolopyrimidine
Pyridine + Pyridine
E.I. du Pont de Nemours & Co.
Dow AgroSciences LLC
Dow AgroSciences LLC.
Dow AgroSciences LLC
Dow AgroSciences LLC
Dow AgroSciences LLC
Dow AgroSciences LLC
Monsanto Technology LLC
Dow AgroSciences LLC
Semicarbazones
Sulfonylurea + Benzoic Acid +
Semicarbazone
Benzoic Acid + Semicarbazone
Benzoic Acid + Semicarbazone
BASF
BASF
BASF
Herbicides shown in bold type contain two or more active ingredients, so they may appear in more than one section of the table.
44
HERBICIDE MODES OF ACTION
Carotenoid Synthesis Inhibitors
Command
Carotenoid Synthesis Inhibitor
Command® Xtra Carotenoid Synthesis Inhibitor +
PPO Inhibitor
Carotenoid Synthesis Inhibitor +
Commence®
Micrutubule Inhibitor
®
CLASS OF CHEMISTRY
Isoxazolidinones
Isoxazolidinone
Isoxazolidinone + Triazolinone
FMC Corporation
FMC Coporation
Isoxazolidinone + Triazolinone
FMC Coporation
Cell Division Inhibitors
Axiom
Define™
Degree®
Degree Xtra ®
Domain™
Dual II Magnum®
®
Guardsman Max®
Expert®
Halex™ GT
Harness®
Harness® Xtra
Lexar®
Lumax®
Micro-Tech®
Outlook®
Radius™
SureStart™
TripleFLEX™
Herbicide
Verdict™
Warrant™
Herbicide
Cell Division Inhibitor + PS II Inhibitor
Cell Division Inhibitor
Cell Division Inhibitor
Cell Division Inhibitor + PS II Inhibitor
Cell Division Inhibitor + PS II Inhibitor
Cell Division Inhibitor
Cell Division Inhibitor + PS II Inhibitor
Cell Division Inhibitor + PS II Inhibitor
+ EPSPS Inhibitor
Cell Division Inhibitor + 4-HPPD
Inhibitor + EPSPS Inhibitor
Cell Division Inhibitor
Cell Division Inhibitor + PS II Inhibitor
Cell Division Inhibitor + 4-HPPD
Inhibitor + PS II Inhibitor
Cell Division Inhibitor + 4-HPPD
Inhibitor + PS II Inhibitor
Cell Division Inhibitor
Cell Division Inhibitor
Cell Division Inhibitor + 4-HPPD
Inhibitor
ALS Inhibitor + Auxin + Cell Division
Inhibitor
Cell Division Inhibitor + Auxin + ALS
Inhibitor
PPO Inhibitor + Cell Division Inhibitor
Cell Division Inhibitor
Amides
Amide + Triazine
Amide
Amide
Amide + Triazine
Amide + Triazine
Amide
Amide + Triazine
Amide + Triazine + Glycine
Bayer
Bayer
Monsanto Technology LLC
Monsanto Technology LLC
Bayer
Syngenta
BASF
Syngenta
Amide + Triketone + Glycine
Syngenta
Amide
Amide + Triazine
Amide + Triketone + Triazine
Monsanto Technology LLC
Monsanto Technology LLC
Syngenta
Amide + Triketone + Triazine
Syngenta
Amide
Amide
Amide + Isoxazole
Monsanto Technology LLC
BASF
Bayer
Triazolopyrimidine + Pyridine +
Amide
Amide + Pyridine +
Triazolopyrimidine
Pyrimidinedione + Chloroacetamide
Amide
Dow AgroSciences LLC
EPSP Synthase Inhibitors
Expert®
Flexstar® GT
Glyphomax®
Halex™ GT
Roundup
PowerMAX®
Roundup
WeatherMAX®
Touchdown®
Monsanto Technology LLC
BASF
Monsanto Technology LLC
Glycines
Cell Division Inhibitor + PS II Inhibitor
+ EPSPS Inhibitor
PPO Inhibitor + EPSPS Inhibitor
EPSPS Inhibitor
Cell Division Inhibitor + 4-HPPD
Inhibitor + EPSPS Inhibitor
EPSPS Inhibitor
Glycine + Triazine
Syngenta
Diphenyl Ether + Glycine
Glycine
Amide + Isoxazole + Glycine
Syngenta
Dow AgroSciences LLC
Syngenta
Glycine
Monsanto Technology LLC
EPSPS Inhibitor
Glycine
Monsanto Technology LLC
EPSPS Inhibitor
Glycine
Syngenta
Glutamine Synthase Inhibitors
Ignite®
Liberty®
Liberty® ATZ
TRADEMARK OWNER
GS Inhibitor
GS Inhibitor
GS Inhibitor + PS II Inhibitor
Phosphinic Acids
Phosphinic Acid
Phosphinic Acid
Phosphinic Acid + Triazine
Bayer
Bayer
Bayer
Herbicides shown in bold type contain two or more active ingredients, so they may appear in more than one section of the table.
45
Corn Diagnostic Guide
HERBICIDE MODES OF ACTION
CLASS OF CHEMISTRY
4-Hydroxyphenyl-Pyruvate-Dioxygenase
Inhibitor
TRADEMARK OWNER
Isoxazole
Balance®
Balance® Flex
Balance® Pro
Corvus™
Laudis™
4-HPPD Inhibitor
4-HPPD Inhibitor
4-HPPD Inhibitor
4-HPPD Inhibitor
4-HPPD Inhibitor
Isoxazole
Isoxazole
Isoxazole
Isoxazole
Isoxazole
Bayer
Bayer
Bayer
Syngenta
Bayer
Radius™
Cell Division Inhibitor + 4-HPPD
Inhibitor
Amide + Isoxazole
Bayer
4-Hydroxyphenyl-Pyruvate-Dioxygenase
Inhibitor
Callisto®
Halex™ GT
4-HPPD Inhibitor
Cell Division Inhibitor + 4-HPPD
Inhibitor + EPSPS Inhibitor
4-HPPD Inhibitor
Cell Division Inhibitor + 4-HPPD
Inhibitor + PS II Inhibitor
Cell Division Inhibitor + 4-HPPD
Inhibitor + PS II Inhibitor
ALS Inhibitor + 4-HPPD Inhibitor
Impact®
Lexar®
Lumax®
Realm™ Q
Microtubule Inhibitors
Commence
®
Pendimax®
Prowl®
Prowl® H2O
Pursuit® Plus
Sonalan®
Squadron®
Steel®
Treflan®
trifluralin
Carotenoid Synthesis Inhibitor +
Micrutubule Inhibitor
Micrutubule Inhibitor
Micrutubule Inhibitor
Micrutubule Inhibitor
ALS Inhibitor + Micrutubule Inhibitor
Micrutubule Inhibitor
ALS Inhibitor + Micrutubule Inhibitor
ALS Inhibitor + ALS Inhibitor +
Micrutubule Inhibitor
Micrutubule Inhibitor
Micrutubule Inhibitor
Protoporphyrinogen Oxidase Inhibitors
Blazer®
Cobra®
FlexStar®
Flexstar® GT
Goal®
Phoenix™
Reflex®
Storm®
Ultra Blazer®
PPO Inhibitor
PPO Inhibitor
PPO Inhibitor
PPO Inhibitor + EPSPS Inhibitor
PPO Inhibitor
PPO Inhibitor
PPO Inhibitor
PPO Inhibitor + PS II Inhibitor
PPO Inhibitor
Protoporphyrinogen Oxidase Inhibitors
Gangster
ALS Inhibitor + PPO Inhibitor
Resource®
Valor® SX
Valor® XLT
PPO Inhibitor
PPO Inhibitor
ALS Inhibitor + PPO Inhibitor
®
Triketones
Triketone
Amide + Triketone + Glycine
Sygenta
Sygenta.
Triketone
Triketone
Amvac Chemical Corporation
Syngenta
Amide + Triketone + Triazine
Sygenta
Sulfonylurea + Triketone
E.I. du Pont de Nemours & Co.
Dinitroanilines
Isoxazolidinone + Dinitroaniline
FMC Corporation
Dinitroaniline
Dinitroaniline
Dinitroaniline
Imidazolinone + Dinitroaniline
Dinitroaniline
Imidazolinone + Dinitroaniline
Imidazolinone + Imidazolinone +
Dinitroaniline
Dinitroaniline
Dinitroaniline
Dow AgroSciences LLC
BASF
BASF
BASF
Dow AgroSciences LLC
BASF
BASF
Dow AgroSciences LLC
Generic chemical name
Diphenyl Ethers
Diphenyl Ether
Diphenyl Ether
Diphenyl Ether
Diphenyl Ether + Glycine
Diphenyl Ether
Diphenyl Ether
Diphenyl Ether
Diphenyl Ether + Benzothiadiazole
Diphenyl Ether
United Phosphorus, Inc.
Valent USA Corporation
Syngenta
Syngenta
Dow AgroSciences LLC
Valent USA Corporation
Syngenta
United Phosphorus, Inc.
United Phosphorus, Inc.
Phenylphthalimides
Triazolopyrimidine +
Phenylphthalimide
Phenylphthalimide
Phenylphthalimide
Phenylphthalimide + Sulfonylurea
Valent USA Corporation
Valent USA Corporation
Valent USA Corporation
Valent USA Corporation
Herbicides shown in bold type contain two or more active ingredients, so they may appear in more than one section of the table.
46
HERBICIDE MODES OF ACTION
CLASS OF CHEMISTRY
Protoporphyrinogen Oxidase Inhibitors
Optill™
Sharpen™
Verdict™
ALS Inhibitor + PPO Inhibitor
PPO Inhibitor
PPO Inhibitor + Cell Division Inhibitor
Pyrimidinediones
Imidazolinone + Pyrimidinedione
Pyrimidinedione
Pyrimidinedione + Chloroacetamide
Protoporphyrinogen Oxidase Inhibitors
Aim®
Authority®
Authority® Assist
Authority™ First
Authority® XL
Command® Xtra
Gauntlet®
PPO Inhibitor
PPO Inhibitor
ALS Inhibitor + PPO Inhibitor
ALS Inhibitor + PPO Inhibitor
ALS Inhibitor + PPO Inhibitor
Carotenoid Synthesis Inhibitor +
PPO Inhibitor
ALS Inhibitor + PPO Inhibitorr
PPO Inhibitor
diquat
Reward®
Gramoxone
Inteon™
PS I Inhibitor
PS I Inhibitor
PS I Inhibitor
Triazolinones
FMC Corporation
FMC Corporation
FMC Corporation
FMC Corporation
FMC Corporation
FMC Corporation
Triazolopyrimidine + Triazolinone
Triazolinone
FMC Corporation
Bipyridiliums
Bipyridilium
Bipyridilium
Bipyridilium
Photosystem II Inhibitors
Basagran
Laddok®
Storm®
PS II Inhibitor
PS II Inhibitor + PS II Inhibitor
PPO Inhibitor + PS II Inhibitor
®
PS II Inhibitor
PS II Inhibitor
PS II Inhibitor
Benzothiadiazole
Benzothiadiazole + Triazine
Diphenyl Ether + Benzothiadiazole
PS II Inhibitor
PS II Inhibitor
Cell Division Inhibitor + PS II Inhibitor
ALS Inhibitor + PS II Inhibitor
Cell Division Inhibitor + PS II Inhibitor
Cell Division Inhibitor + PS II Inhibitor
Cell Division Inhibitor + PS II Inhibitor
Cell Division Inhibitor + PS II Inhibitor
PS II Inhibitor + PS II Inhibitor
Cell Division Inhibitor + 4-HPPD
Inhibitor + PS II Inhibitor
GS Inhibitor + PS II Inhibitor
Liberty® ATZ
Cell Division Inhibitor + 4-HPPD
Lumax®
Inhibitor + PS II Inhibitor
Auxin + PS II Inhibitor
Marksman®
PS II Inhibitor
Princep®
PS II Inhibitor
Sencor®
Steadfast® ATZ ALS Inhibitor + ALS Inhibitor +
PS II Inhibitor
PS II Inhibitor
Winfield Solutions, LLC
Bayer
Winfield Solutions, LLC
Triazines
Triazine
Triazine
Amide + Triazinone
Sulfonylurea + Triazine
Amide + Triazine
Amide + Triazine
Amide + Triazine
Amide + Triazine
Benzothiadiazole + Triazine
Amide + Isoxazole + Triazine
Syngenta
Generic chemical name
Bayer
E.I. du Pont de Nemours & Co.
Monsanto Technology LLC
Bayer
BASF
Monsanto Technology LLC
BASF
Syngenta
Phosphonic Acid + Triazine
Amide + Isoxazole + Triazine
Bayer
Syngenta
Benzoic Acid + Triazine
Triazine
Triazine
Sulfonylurea + Sulfonylurea +
Triazine
BASF
Syngenta
Bayer
E.I. du Pont de Nemours & Co
Photosystem II Inhibitors
Lorox®
BASF
BASF
United Phosphorus, Inc.
Nitriles
Nitrile
Nitrile
Nitrile
Photosystem II Inhibitors
Aatrex®
atrazine
Axiom®
Canopy®
Degree Xtra®
Domain™
Guardsman Max®
Harness® Xtra
Laddok®
Lexar®
Generic chemical name
Syngenta
Syngenta
Benzothiadiazoles
Photosystem II Inhibitors
Bison®
Buctril®
Moxy®
BASF
BASF
BASF
Triazolinone
Triazolinone
Imidazolinone + Triazolinone
Triazolopyrimidine + Triazolinone
Sulfonylurea + Triazolinone
Isoxazolidinone + Triazolinone
Photosystem I Electron Diversion
®
TRADEMARK OWNER
Ureas
Urea
E.I. du Pont de Nemours & Co.
Herbicides shown in bold type contain two or more active ingredients, so they may appear in more than one section of the table.
47
Corn Diagnostic Guide
Herbicides by Active Ingredient
and Mode of Action
HERBICIDE
ACTIVE INGREDIENT
MODE OF ACTION
2,4-D
2,4-D
Auxin
AAtrex®
Atrazine
PS II Inhibitor
Accent
Nicosulfuron
ALS Inhibitor
Accent Gold®
Clopyralid + Flumetsulam + Nicosulfuron +
Rimsulfuron
ALS Inhibitor + ALS Inhibitor + ALS Inhibitor +
Auxin
Aim®
Carfentrazone
PPO Inhibitor
Assure II
Quizalofop
ACCase Inhibitor
atrazine
Atrazone
PS II Inhibitor
Authority®
Sulfentrazone
PPO Inhibitor
Authority Assist
Imazethapyr + Sulfentrazone
ALS Inhibitor + PPO Inhibitor
®
®
®
Authority First
Cloransulam + Sulfentrazone
ALS Inhibitor + PPO Inhibitor
Authority® XL
Chlorimuron + Sulfentrazone
ALS Inhibitor + PPO Inhibitor
Axiom
Flufenacet + Metribuzin
Cell Division Inhibitor + PS II Inhibitor
Balance
Isoxaflutole
4-HPPD Inhibitor
Balance® Flexx
Isoxaflutole
4-HPPD Inhibitor
Balance Pro
Isoxaflutole
4-HPPD Inhibitor
Banvel
Dicamba
Auxin
Basagran
Bentazon
PS II Inhibitor
Beacon®
Primisulfuron
ALS Inhibitor
Bison
Bromoxynil
PS II Inhibitor
Blazer
Aciflourfen
PPO Inhibitor
Broadstrike™
Flumetsulam
ALS Inhibitor
Buctril
Bromoxynil
PS II Inhibitor
Butyrac
2,4-DB
Auxin
Callisto®
Mesotrione
4-HPPD Inhibitor
Chlorimuron + Metribuzin
ALS Inhibitor + PS II Inhibitor
Celebrity Plus
Dicamba + Diflufenzopyr + Nicosulfuron
ALS Inhibitor + Auxin + Auxin Transport Inhibitor
Clarity
Dicamba
Auxin
Classic®
Chlorimuron
ALS Inhibitor
Lactofen
PPO Inhibitor
Command
Clomazone
Carotenoid Synthesis Inhibitor
Command® Xtra
Clomazone + Sulfentrazone
Carotenoid Synthesis Inhibitor + PPO Inhibitor
Commence®
Clomazone + Trifluralin
Carotenoid Synthesis Inhibitor + Microtubule
Inhibitor
Corvus™
Isoxaflutole
4-HPPD Inhibitor
2,4-D + Triclopyr
Auxin + Auxin
™
®
®
®
®
®
®
®
®
®
Canopy
®
®
®
Cobra
®
®
Crossbow
®
48
Herbicides by Active Ingredient
and Mode of Action (cont.)
HERBICIDE
ACTIVE INGREDIENT
MODE OF ACTION
Define™
Flufenacet
Cell Division Inhibitor
Degree®
Acetochlor
Cell Division Inhibitor
Acetochlor + Atrazine
Cell Division Inhibitor + PS II Inhibitor
diquat
Diquat
PS I Inhibitor
Distinct®
Dicamba + Diflufenzopyr
Auxin + Auxin Transport Inhibitor
Flufenacet + Metribuzin
Cell Division Inhibitor + PS II Inhibitor
Degree Xtra
Domain
®
®
Dual II Magnum
Metolachlor
Cell Division Inhibitor
Exceed®
Primisulfuron + Prosulfuron
ALS Inhibitor + ALS Inhibitor
Expert®
Atrazine + Glyphosate + Metolachlor
Cell Division Inhibitor + PS II Inhibitor + EPSPS
Inhibitor
FirstRate®
Cloransulam
ALS Inhibitor
Flexstar
Fomesafen
PPO Inhibitor
®
®
Fusilade DX
Fluazifop
ACCase Inhibitor
Flexstar® GT
Fomesafen + Glyphosate
PPO Inhibitor + EPSPS Inhibitor
Fusion
Fenoxaprop + Fluazifop
ACCase Inhibitor + ACCase Inhibitor
Gangster
Cloransulam + Flumioxazin
ALS Inhibitor + PPO Inhibitor
Gauntlet
Cloransulam + Sulfentrazone
ALS Inhibitor + PPO Inhibitor
Glyphomax®
Glyphosate
EPSPS Inhibitor
Goal
Oxyfluorfen
PPO Inhibitor
Gramoxone Inteon™
Paraquat
PS I Inhibitor
Guardsman Max®
Atrazine + Dimethenamid
Cell Division Inhibitor + PS II Inhibitor
Halex™ GT
Glyphosate + Mesotrione + Metolachlor
Cell Division Inhibitor + 4-HPPD Inhibitor +
EPSPS Inhibitor
Harness®
Acetochlor
Cell Division Inhibitor
Harness Xtra
Acetochlor + Atrazine
Cell Division Inhibitor + PS II Inhibitor
Hoelon
®
®
®
®
®
®
Diclofop
ACCase Inhibitor
Hornet®
Clopyralid + Flumetsulam
ALS Inhibitor + Auxin
Ignite
Glufosinate
GS Inhibitor
Topramezone
4-HPPD Inhibitor
Laddok
Atrazine + Bentazon
PS II Inhibitor + PS II Inhibitor
Laudis™
Tembotrione
4-HPPD Inhibitor
Lexar®
Atrazine + Mesotrione + Metolachlor
Cell Division Inhibitor + 4-HPPD Inhibitor + PS II
Inhibitor
Glufosinate
GS Inhibitor
Liberty ATZ
Atrazine + Glufosinate
GS Inhibitor + PS II Inhibitor
Lightning
Imazapyr + Imazethapyr
ALS Inhibitor + ALS Inhibitor
Linuron
PS II Inhibitor
®
®
Impact
®
Liberty®
®
Lorox®
49
®
Corn Diagnostic Guide
Herbicides by Active Ingredient
and Mode of Action (cont.)
HERBICIDE
ACTIVE INGREDIENT
MODE OF ACTION
Atrazine + Mesotrione + Metolachlor
Cell Division Inhibitor + 4-HPPD Inhibitor + PS II
Inhibitor
Marksman®
Atrazine + Dicamba
Auxin + PS II Inhibitor
Micro-Tech
Alochlor
Cell Division Inhibitor
Moxy™
Bromoxynil
PS II Inhibitor
NorthStar
Dicamba + Primisulfuron
ALS Inhibitor + Auxin
Optill
Imazethapyr + Saflufenacil
ALS Inhibitor + PPO Inhibitor
Option®
Foramsulfuron
ALS Inhibitor
Outlook
Dimethenamid
Cell Division Inhibitor
Peak
Prosulfuron
ALS Inhibitor
Pendimax®
Pendimethalin
Microtubule Inhibitor
Permit
Halosulfuron
ALS Inhibitor
Phoenix™
Lactofen
PPO Inhibitor
Poast Plus®
Sethoxydim
ACCase Inhibitor
Poast
Sethoxydim
ACCase Inhibitor
Princep
Simazine
PS II Inhibitor
®
Prowl
Pendimethalin
Microtubule Inhibitor
Prowl® H2O
Pendimethalin
Microtubule Inhibitor
Pursuit
Imazethapyr
ALS Inhibitor
Lumax®
®
®
™
®
®
®
®
®
®
Pursuit Plus
Imazethapyr + Pendimethalin
ALS Inhibitor + Mictrotubule Inhibitor
Python®
Flumetsulam
ALS Inhibitor
Radius™
Flufenacet + Isoxaflutole
Cell Division Inhibitor + 4-HPPD Inhibitor
Raptor
Imazamox
ALS Inhibitor
Realm™ Q
Rimsulfuron + Mesotrione
ALS Inhibitor + 4-HPPD Inhibitor
Reflex
Fomesafen
PPO Inhibitor
Resolve Q
Rimsulfuron + Thifensulfuron
ALS Inhibitor + ALS Inhibitor
Resource
Flumiclorac
PPO Inhibitor
Reward®
Diquat
PS I Inhibitor
Roundup PowerMAX
Glyphosate
EPSPS Inhibitor
Roundup
WeatherMAX®
Glyphosate
EPSPS Inhibitor
Scepter®
Imazaquin
ALS Inhibitor
Select
Clethodim
ACCase Inhibitor
Select MAX®
Clethodim
ACCase Inhibitor
Sencor
Metribuzin
PS II Inhibitor
Saflufenacil
PPO Inhibitor
®
®
®
®
®
®
®
®
Sharpen
™
50
Herbicides by Active Ingredient
and Mode of Action (cont.)
HERBICIDE
ACTIVE INGREDIENT
MODE OF ACTION
Sonalan®
Ethalfluralin
Microtubule Inhibitor
Spirit®
Primisulfuron + Prosulfuron
ALS Inhibitor + ALS Inhibitor
Imazaquin + Pendimethalin
ALS Inhibitor + Microtubule Inhibitor
Status
Dicamba + Diflufenzopyr
Auxin + Auxin Transport Inhibitor
Steadfast®
Nicosulfuron + Rimsulfuron
ALS Inhibitor + ALS Inhibitor
Steadfast ATZ
Atrazine + Nicosulfuron + Rimsulfuron
ALS Inhibitor + ALS Inhibitor + PS II Inhibitor
Steel
Imazaquin + Imazethapyr + Pendimethalin
ALS Inhibitor + ALS Inhibitor + Microtubule Inhibitor
Stinger®
Clopyralid
Auxin
Squadron
®
®
®
®
Storm
Bentazon
PPO Inhibitor + PS II Inhibitor
™
SureStart
Acetochlor + Clopyralid + Flumetsulam
ALS Inhibitor + Auxin + Cell Division Inhibitor
SureStart™
Acetochlor + Clopyralid + Flumetsulam
ALS Inhibitor +Auxin + Cell Division Inhibitor
Synchrony XP
Chlorimuron + Thifensulfuron
ALS Inhibitor + ALS Inhibitor
Tordon
Picloram
Auxin
Touchdown
Glyphosate
EPSPS Inhibitor
Transline®
Clopyralid
Auxin
Treflan
Trifluralin
Microtubule Inhibitor
trifluralin
Trifluralin
Microtubule Inhibitor
TripleFLEX™ Herbicide
Acetochlor + Clopyralid + Flumetsulam
Cell Division Inhibitor + Auxin + ALS Inhibitor
Ultra Blazer
Acifluorfen
PPO Inhibitor
®
®
®
®
®
®
Valor SX
Flumioxazin
PPO Inhibitor
Valor® XLT
Flumioxazin + Chlorimuron
PPO Inhibitor + ALS Inhibitor
Verdict
Dimethenamid + Saflufenacil
PPO Inhibitor + Cell Division Inhibitor
Warrant Herbicide
Acetochlor
Cell Division Inhibitor
WideMatch
Clorpyralid + Fluroxypyr
Auxin + Auxin
Yukon®
Dicamba + Halosulfuron
ALS Inhibitor + Auxin
®
™
™
®
51
Corn Diagnostic Guide
9
Nutrient Deficiency
Symptoms
This section describes visual symptoms of moderate to severe nutrient deficiencies. These deficiencies are not
always due to insufficient nutrient supplies in the soil. Symptoms are often induced by poor root development,
root damage, unfavorable soil conditions (dry, water-logged, or compacted), or unfavorable weather. Nutrient
availability is highly variable, strongly influenced by management decisions, and is only one component of soil
productivity. Therefore, correction does not automatically require application of the suspected nutrient.
Mobile elements, like nitrogen, may become unavailable to plants because of leaching or gasification. Soil
compaction, dry soil, soil where water has ponded, and inadequate rooting are examples of soil and plant
conditions that may limit nutrient uptake. Specific nutrient deficiencies can be difficult to diagnose accurately.
Soil and/or plant analysis may help identify and establish the cause of the symptoms. With these analyses be
aware of possible nutrient interactions that may influence results.
Boron (B)
Iron (Fe)
Boron deficiency is rare. Irregular white spots occur
between leaf veins and may combine into white stripes
with a raised waxy appearance. Bush-shaped plants
often fail to produce a tassel or ear. Deficiency is favored
by drought, high pH and sandy soil low in organic matter.
Boron toxicity can cause yellow, dying leaf margins and
tips.
Iron deficiency symptoms
are rare. The upper leaves
turn white between the veins,
affecting the entire length.
Symptoms are favored by
high pH (alkaline) soil, cool
weather, and wet, compacted
soil.
Calcium (Ca)
Symptoms of calcium deficiency are rare. Seedling leaf
tips adhere to the next lower leaf, resulting in laddering
effect and failure to unfurl normally. Deficiency is favored
by very low pH (below 5.5) and high magnesium or
potassium level.
Copper (Cu)
Copper deficiency is rare. Young leaves yellow as they
emerge from the whorl and may die at the tip and edges.
Stalks are soft and flexible. Deficiency is favored by high
organic matter soils.
Magnesium (Mg)
Yellow-white streaking occurs
between veins of lower leaves
if magnesium is deficient.
Eventually, margins and
tips of older leaves become
reddish-purple, then die.
Deficiency is favored by
low pH, sandy soil and high
potassium levels.
52
Manganese (Mn)
Manganese deficiency is
rare. The area between leaf
veins turns pale green-yellow.
Stalks are thin and limber.
Symptoms are favored by
peat or muck soil, high pH
and sandy soil high in organic
matter.
Molybdenum (Mo)
Molybdenum deficiency is rare. Young leaves sometimes
twist, wilt and die along margins. Older leaves die at
the tip, along margins and between veins. Deficiency is
favored by low pH and strong soil weathering.
Nitrogen (N)
Nitrogen-deficient
plants are spindly,
pale and stunted.
Lower leaves
develop a yelloworange color in the
shape of an inverted
“V” beginning at the
tip and following
the midvein. Leaves
may begin to die (fire) at the tip. Symptoms advance up
the plant to younger leaves. Ears are small and pinched
at the tip. Symptoms are favored by cold, ponded, dry, or
low organic matter soil, and incorporation of low-nitrogen
residues.
Phosphorus (P)
Leaves of young phosphorusdeficient plants are bluishgreen and slightly narrowed,
turning reddish-purple starting
at the tips and along the
edges. Leaf tips may die. If
conditions for phosphorous
uptake improve, newer
leaves may be symptom-free.
53
Corn Diagnostic Guide
Symptoms are seldom observed on knee-high and larger
plants. Ears may be small and misshapen, twisted with
one or more kernel rows missing on one side.
Potassium (K)
Symptoms of potassium
deficiency are seldom seen
before plants are knee-high.
Edges of lower leaves turn
yellow and die (fire), starting
at the tip. Leaves may break
away. Plants are shortened.
Ears are small and chaffy
with poor tip-fill. Deficiency is
favored by wet or compacted
soils, sandy or strongly weathered soil, and organic soil.
Heavy potassium removal by previous crop can also favor
deficiency.
Sulfur (S)
Deficiency of sulfur causes
stunted, slow-growing and
yellow plants. Yellowing
occurs between veins,
especially of younger (upper)
leaves. Older plants rarely
show symptoms. Symptoms
are favored by cold, wet soil,
low pH, and low organic
matter.
Zinc (Zn)
Symptoms of zinc deficiency
are rare beyond the seedling
stage. Yellow to white
bleached bands appear on
the lower part of leaves while
the midvein, margins and tip
remain green. Newly affected
leaves are sometimes
described as “white buds.”
The deficiency is favored
by high soil phosphorus, high pH, cool, wet soil and low
organic matter – such as from exposed subsoil.
Index
4-HPPD Inhibitors ........ . . . . . . . . . . 42
ACCase Inhibitors .................... 40
Acetanilides . . . . ....................... 41
ALS Inhibitors..........................40
Amides .................................41
Anthracnose ...........................24
Anthracnose Stalk Rot ... . . . . . . . .... 28
Aphids ................................. 31
Armyworms ............................32
Aryloxyphenoxy Propionic Acids ... 40
Aspergillus Ear and Kernel Rot ......29
Auxin Transport Inhibitors ........... 41
Bacterial Leaf Blight ................. 24
Bacterial Stalk Rot ................... 28
Bacterial Wilt .......................... 24
Benzoic Acids .........................41
Benzothiadiazoles .................... 42
Billbug ... . . . . .......................... 32
Bipyridiliums .......................... 42
Black Cutworm ....................... 35
Blister Smut ........................... 26
Boil Smut .............................. 26
Boron .................................. 52
Calcium ................................ 52
Carotenoid Synthesis Inhibitors .... 41
Cell Division Inhibitors ............... 41
Cereal Leaf Beetle ................... 32
Charcoal Rot .......................... 28
Chinch Bug .................... . . . . ... 32
Cladosporium Ear Rot .............. 29
Common Corn Rust ................. 24
Common Corn Smut ................ 26
Common Stalk Borer ................ 32
Copper ................................ 52
Corn Borer ........................... 33
Corn Earworm ....................... 33
Corn Leaf Aphid ...... . . . . . . . ....... 31
Corn Lethal Necrosis .... . . . . . . .... 27
Corn Root Aphid .................... 31
Corn Rootworm ..................... 34
Corn Stunt Spiroplasma .... . . . . ...27
Crazy Top .............................27
Cutworm .............................. 35
Cyclohexanediones .......... . . . . .... 40
Dinitroanilines ................. . . ...... 42
Diphenyl Ethers .............. . . ...... 42
Diplodia Ear Rot ............ . . . ....... 30
Diplodia Stalk Rot ............ . . ......
EPSP Synthase Inhibitors . . . .......
European Corn Borer .... . . . . ... . . . .
Eyespot ............... . . . . . . . . . .......
Fall Armyworm ...... . . . . . . . . .......
Flea Beetle ................... . . .......
Fusarium Kernel or Ear Rot ... . . . ...
Fusarium Stalk Rot ..... . . . . . . . . .....
Gibberella Ear Rot ....... . . . . . . . . . ...
Gibberella Stalk Rot ......... . . . . . ...
Glutamine Synthase Inhibitors ......
Glycines ....................... . .......
Goss’s Wilt .................... . .......
Grape Colaspis ... . . . . . . . . . . . . .......
Grasshopper ........... . . . . . . . . ......
Gray Leaf Spot ............. . . . .......
Head Smut ............ . . . . . . . . .......
Helminthosporium Leaf Spot .. . . . ..
High Plains Virus ........... . . . . . . ....
Holcus Spot ............... . . . . .......
Imidazolinones ... . . . ........ . . .......
Iron ........................... . . . .......
Isoxazoles ... . . . ............. . . .......
Isoxazolidinones ... . . . ...... . . .......
Japanese Beetle ... . . . ...... . . .......
Kernel Red Streak ....... . . . . . . . . ....
Leaf Freckles and Wilt ...............
Leaf Miner ................... . . . .......
Lesser Cornstalk Borer ... . . . . . . ....
Magnesium ................. . . . .......
Maize Chlorotic Dwarf Virus .. . . . ...
Maize Dwarf Mosaic Virus .. . . . . . ...
Manganese ................. . . . .......
Mexican Corn Rootworm . . . . .......
Microtubule Inhibitors ..... . . . .......
Molybdenum ........ . . . . . . . . . . .......
Nebraska Bacterial Wilt and
Leaf Freckles ............... . . . .......
Nitriles ........... . . . . . . . . . . . . . . .......
Nitrogen ........... . . . . . . . . . . . . .......
Northern Corn Leaf Blight ...........
Northern Corn Rootworm ...........
Northern Leaf Spot ......... . . .......
Penicillium Ear Rot ............ .......
Phaeosphaeria Leaf Spot .. . . . ......
Phenoxys . . . . . . . . ........... . . . .......
Phosphinic Acids .......... . . . .......
28
41
33
26
32
35
30
29
30
29
41
41
26
35
35
25
26
25
27
25
40
52
42
41
36
37
26
36
36
52
27
27
53
34
42
53
25
42
53
26
34
25
30
26
41
41
Phosphorus ................. . . . ....... 53
Photosystem I Electron Diversion .. 42
Photosystem II Inhibitors - mobile .. 42
Photosystem II Inhibitors - nonmobile .. 42
Physoderma Brown Spot . . . . . ...... 26
Picnic Beetle ................ . . . ....... 36
Pinched Ear Syndrome ........... . .. 40
Potassium ................... . . . ....... 53
PPO Inhibitors .............. . . . ....... 42
Pyridine Carboxylic Acids .. . . . ..... 41
Pyrimidines . . . . . . . .................... 42
Pythium Stalk Rot .. . . . .............. . 29
Red Root Rot ............... . . . ....... 29
Sap Beetle .................. . . . ....... 36
Scavenger Beetle ..................... 36
Seed Corn Beetle .... . . . . . .... ....... 36
Seed Corn Maggot .. . . . ............. 36
Semicarbazones ...... . . . . . . . ....... 41
Slug ..................................... 36
Sorghum Downy Mildew ... . . . ...... 28
Southern Corn Leaf Blight .. . . . ..... 26
Southern Corn Rootworm .. . . . . .... 34
Southern Corn Rust .................. 26
Southwestern Corn Borer ........... 33
Spider Mite ............................ 37
Stewart’s Disease .. . . . . . ............. 24
Stewart’s Wilt .. . . . . . . ................. 24
Stink Bug .............................. 37
Sulfonylureas ......................... 40
Sulfur ................................... 53
Synthetic Auxins ..................... 41
Thrips ................................... 37
Triazines ................................ 42
Triazolinones .......................... 42
Triazolopyrimidines ................... 40
Trichoderma Ear Rot ................. 30
Triketones .............................. 42
True Armyworm ....................... 32
Ureas ................................... 42
Webworm ... . . . . . . . ................... 37
Western Bean Cutworm ............. 35
Western Corn Rootworm .. . . . . . . ... 34
Wheat Curl Mite ... . . . . . . . ............ 38
White Grub ............................ 38
Wireworm .............................. 38
Zinc ..................................... 48
54
Notes
Corn Diagnostic Guide
Monsanto Company is a member of Excellence Through Stewardship® (ETS). Monsanto products
are commercialized in accordance with ETS Product Launch Stewardship Guidance, and in compliance
with Monsanto’s Policy for Commercialization of Biotechnology-Derived Plant Products in Commodity
Crops. This product has been approved for import into key export markets with functioning regulatory
systems. Any crop or material produced from this product can only be exported to, or used, processed
or sold in countries where all necessary regulatory approvals have been granted. It is a violation of
national and international law to move material containing biotech traits across boundaries into nations
where import is not permitted. Growers should talk to their grain handler or product purchaser to confirm
their buying position for this product. Excellence Through Stewardship ® is a registered trademark of
Biotechnology Industry Organization.
B.t. products may not yet be registered in all states. Check with your Monsanto representative for the
registration status in your state.
Individual results may vary, and performance may vary from location to location and from year to year.
This result may not be an indicator of results you may obtain as local growing, soil and weather conditions
may vary. Growers should evaluate data from multiple locations and years whenever possible.
ALWAYS READ AND FOLLOW PESTICIDE LABEL DIRECTIONS. Roundup Ready® crops contain
genes that confer tolerance to glyphosate, the active ingredient in Roundup® brand agricultural herbicides.
Roundup® brand agricultural herbicides will kill crops that are not tolerant to glyphosate. Degree ®,
Harness ®, TripleFLEX ™ Herbicide, and Warrant ™ Herbicide are not registered in all states. Degree ®,
Harness ®, TripleFLEX™ Herbicide, and Warrant™ Herbicide may be subject to use restrictions in some
states. Degree Xtra®, Harness®, and Micro-Tech® are restricted use pesticides and are not registered in
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tank mix product formulations for compatibility or performance other than specifically listed by brand name.
Always predetermine the compatibility of tank mixtures by mixing small proportional quantities in advance.
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