Weed Management in
Potato Cropping Systems
Pamela J.S. Hutchinson
Potato Cropping Systems Weed Scientist
Aberdeen Research & Extension Center
Weed Management in Potatoes:
Lecture topics

Weed – Potato interference

Major problem weeds


Integrated weed management
strategies for potatoes
Herbicide resistance management
Competition for light, water, nutrients
Definition: A plant out of place
Harvest interference
Direct tuber damage: quackgrass rhizome
Weed – Potato Interference

Weeds may host other pests
detrimental to potatoes such as
insects, disease, nematodes
e.g. hairy nightshade hosts potato virus
Y (PVY) and green peach aphid vector
Green peach aphid (Myzus persicae)
Weeds in Potato Cropping Systems



Weed life cycles
Major broadleaf and grass weeds
Competition with potatoes e.g. hairy
nightshade

Weed identification
• Refer to PPS Chapter 13

Weed ecology: dormancy, seed-bank,
germination/emergence relative to potatoes
 Refer to PPS Chapter 13
Weeds in Potato Cropping Systems



Biennial
Perennial
Annual
• Winter and summer
Weed – Life Cycle
Biennial
Second
year
First year
Field pennycress: Winter annual/biennial
Weed – Life Cycle

Perennials
• Live for 3 or more years
• Usually have an extensive stolon or root
system
Canada thistle
Quackgrass
Weed – Life Cycle
Summer Annual
Winter Annual
Fall
Fall
Summer
Early
Summer
Spring
Spring
Common Weeds in Potatoes:
Annual broadleaves and grasses









Hairy nightshade – Solanum sarrachoides
Redroot pigweed – Amaranthus retroflexus
Common lambsquarters – Chenopodium album
Kochia – Kochia scoparia
Russian thistle – Salsola iberica
Common purslane – Portulaca oleracea
Green foxtail – Seteria viridis
Barnyardgrass – Echinochloa crus-galli
Wild oat – Avena fatua
Redroot pigweed
Common lambsquarters
Kochia
Russian thistle
Russian thistle
Common purslane
Green foxtail
barnyard grass
Barnyardgrass
Wild oats
Hairy Nightshade

Recent grower survey
results (IPM/Idaho
Potato Conference)
Hairy nightshade control is
of great concern to many
Idaho potato growers
Hairy Nightshade
(Solanum sarrachoides Sendt.)



Same family as potato
Annual – 12 to 24 inches
Begins germination in early spring and
continues germinating
throughout the summer

Produces flowers and fruit until
the end of the growing season in
PNW
• plants emerging as late as 6 wk
before a killing frost can flower and
produce berries with viable seed
• light frost does not kill
Hairy Nightshade
Sometimes mistaken
for cutleaf nightshade
cutleaf nightshade

hairy nightshade
(Solanum sarrachoides Sendt.)
• Leaf surface/
stems have
glandular hairs
• Leaves can have smooth
to serrated edges
Hairy Nightshade

A large plant can produce
1700+ berries


Innate dormancy for
4+ months after maturity


10 to 35 seeds per berry
Seed buried in the field
developed dormancy when
exposed to high
temperatures
Longevity in soil:
5 yrs = 90% germination
8 yrs = 2% germination
Reports of germination
after 39 yrs in soil
Hairy Nightshade




Seed production example
800 berries/plant
x 10 seeds/berry
= 8,000 seeds/plant!
10 plants/sq ft in our
nontreated checks
43,560 sq ft/A
43,560 x 10 plants x 8,000
seeds/plant
= 3,484,800,000 seeds/A !!!
Hairy Nightshade: research trials
• Competition: what hairy nightshade density does it
take to reduce potato yield?
• Critical interference period: what’s the period
during the growing season when the presence of the
weed will reduce yield?
Effect of season-long hairy nightshade competition at four densities
on tuber yield of two potato varieties at Aberdeen, ID in 2004 and
2005.
1 hairy nightshade per meter row
Effect of season-long hairy nightshade competition at
four densities on tuber yield of two potato varieties at
Aberdeen, ID in 2004 and 2005.
Variety
Hairy nightshade
Tuber yield
density (per m row) U.S. No. 1 Total
----- % reduction -----
Russet
Norkotah
1
2
3
100
21 *
26 *
27 *
48 *
16 *
20 *
25 *
37 *
Russet
Burbank
1
2
3
100
6
10 *
11 *
21 *
5
9*
9*
19 *
*significantly different than weed-free control
Hairy nightshade critical interference
period in potatoes
• Weed-free for 0, 10, 20, 30, or 40 days after
emergence (DAE)
− Transplanted at emergence and then every 10
days
• Weedy for 0, 10, 20, 30, or 40 DAE
− Transplanted at emergence and then removed
every 10 days
− Maintained weed-free after removal
Effect of hairy nightshade planting and time of
removal on U.S. No. 1 tuber yields
260
240
220
Cwt/A
200
180
160
140
120
100
0
10
20
Days after emergence
30
40
Effect of hairy nightshade planting and time of
removal on U.S. No. 1 tuber yields
5%
Hairy
reduction
nightshade
= 218.5
present
cwt/A
season-long
Must be weed
caused
free 29%
for
at
U.S.
least
No.21
1 loss
DAE
260
240
230 cwt/A
220
Cwt/A
200
180
160
weed free
164 cwt/A
140
120
100
0
10
20
Days after emergence
30
40
Effect of hairy nightshade planting and time of
removal on U.S. No. 1 tuber yields
260
236 cwt/A
240
5% reduction = 224 cwt/A
Cannot be weedy longer
than 7 DAE
220
Cwt/A
200
180
177 cwt/A
160
weedy
140
120
100
0
10
20
Days after emergence
30
40
Effect of hairy nightshade planting and time of
removal on U.S. No. 1 tuber yields
5% reduction if
SOLSA present between
7 and 21 DAE
260
240
220
Cwt/A
200
180
160
weed free
140
weedy
120
100
0
10
20
Days after emergence
30
40
Integrated Weed Management
in Potato Cropping Systems

Makes use of all tools available:
 Biological

Cultural

Chemical
Brassica green manure
fall incorporation
Effect of Fall-incorporated Green Manures on Hairy nightshade
Biomass in Potatoes the Following Growing-season
Green manures planted and incorporated fall 2006,
Potatoes planted spring 2007, hairy nightshade biomass collected July 13, 2007
Potatoes were 18 to 20 inches and hairy nightshade was 14 to 20 inches tall at sampling time
dry wt g/ 0.25 sq m
70
60
50
40
30
20
10
0
None
No
Oilseed
O.
Radish
Green
radish
manure
W
50% oilseed radish
Mustard mix:
50% Oriental
25%/O
75% O.R.
50%/O
25% Oriental
mustard
75% white
50%
Integrated Weed Management
in Potato Cropping Systems



Weed identification
Keep field histories
Map weed infestations


Simple drawings…GPS
Can conduct site specific action depending
on infestation/density
Integrated Weed Management
Weed infestation/density mapping
Canada
thistle
Wild oat
Weeds throughout the field
HNS
Redroot pigweed – moderate
Common
Lambsquarters – moderate
Hairy nightshade – light except
where noted
Wild Oat – light except
in NE section
Integrated Weed Management
in Potato Cropping Systems

Manage weeds throughout crop rotation


Coordinated plan w/ other crops
Important for perennial weed control




Few herbicide options available in potatoes
Minimize herbicide carryover
Reduce selection for resistant weeds
Plant competitive crops in the rotation

winter wheat, winter canola, barley, alfalfa
Integrated Weed Management
in Potato Cropping Systems

Irrigate after harvest of short season
crops like small grains or canola




Plant competitive potato varieties


Promote weed seed germination/emergence
Control seedlings with tillage
Control volunteer grain
Russet Burbank larger plant canopy, indeterminate growth >
Russet Norkotah smaller stature, doesn’t always close over
rows, less shading
Plant certified seed – maintain vigorous
crop growth
Integrated Weed Management
in Potato Cropping Systems

Current practices in potatoes include



Cultivation
Herbicides
NOTE: Combination often more
effective than either alone
Integrated Weed Management
in Potato Cropping Systems

Cultivation +’s




Less expensive than herbicides
No chemical residues
Wind not an issue
Cultivation –’s





Soil compaction, root pruning-crop injury
Heavy infestations = Multiple cultivations
Wet soil interferes with timeliness
In-row weed control difficult
Disease-spread (important in seed areas)
Ideal weed stage to take out with
cultivator – 2-leaf
Can still take out with cultivator:3-4-leaf
Cultivation:Potato size 4-5” o.k.
>8-10” = root pruning
Weeds left on the side-hills by cultivator
Clean cultivation
Integrated Weed Management
in Potato Cropping Systems

Herbicide +’s




very effective
faster to spray than cultivate
often single application vs multiple cultivations
Herbicide –’s




environmental/safety concerns
potential for crop injury
carryover/plant-back restrictions
cost
Herbicide application methods
Ground
Air
Chemigation
Sprinkler incorporation
Integrated Weed Management
in Potato Cropping Systems
Potato herbicide timing



PPI = pre-plant incorporated
PRE = preemergence to crop and/or
weed
POST = postemergence to crop and/or
weed
Integrated Weed Management
in Potato Cropping Systems

PRE application usually follows a hilling
operation which is performed
before/during potato emergence



Builds a hill so developing tubers are not
exposed to sunlight
Takes out germinating and small weeds to
create a “clean bed”
Sometimes combined on same equipment with
reservoir tillage (Dammer-Diker) for irrigation
water retention/slow infiltration
Reservoir tillage (Dammer-diker)
Hilling and Herbicide Application Timing
Plant
Potato
emergence
3-4 weeks
No competition
Row close
~ 5 weeks
Crop starting to compete
Hilling and Herbicide Application Timing
Plant, Hill, Spray
3-4 weeks
Potato
emergence
Row close
~ 5 weeks
Hill and spray at planting – herbicide must be effective for 8-9 weeks
Hilling and Herbicide Application Timing
Plant
Hill/
Spray
3-4 weeks
Row close
~ 5 weeks
Hill just before or after emergence – herbicide application
to bare-ground before potato re-emergence
Herbicide must be effective for ~6 weeks
Hilling destroys emerged weeds
Hilling and Herbicide Application Timing
Plant, Hill
Spray
3-4 weeks
Row close
~ 5 weeks
Spray a preemergence + non-selective herbicide just before
emergence – non-selective herbicide destroys emerged weeds
Integrated Weed Management
in Potato Cropping Systems

Make timely herbicide applications and
incorporation




Apply Preemergence (PRE) herbicides before
weed and/or potato emergence
Incorporate volatile herbicides e.g. Eptam
immediately
Incorporate PRE-applied herbicides ASAP to
move herbicides to weed-seed germination zone
Cultivations performed after PRE herbicide
applications will break the herbicide barrier
and bring up untreated soil
Integrated Weed Management
in Potato Cropping Systems

Time postemergence (POST) herbicide
applications to weed/crop growth stage



maximize weed control/crop safety
Make sure the weeds are actively growing
for best herbicide uptake (irrigation)
Keep field borders clean


grass cover crop
tillage
Kochia along field borders
Integrated Weed Management in Potatoes
Herbicides labeled for use in potatoes






Eptam (EPTC)
Chateau (flumioxazin)
Dual Magnum (s-metolachlor)
Stalwart and others (metolachlor)
Matrix and others (rimsulfuron)
Outlook (dimethenamid-p)
Integrated Weed Management in Potatoes
Herbicides labeled for use in potatoes






Prowl H2O and others (pendimethalin)
Reflex (fomesafen)
Metribuzin (formerly Sencor – now
generic)
Sonalan (ethalfluralin)
Treflan and others (trifluralin)
Lorox/Linex (linuron) – has been east of the
Rockies only, however, we’re working on a
24(c) SLN label, Idaho
Integrated Weed Management in Potatoes
Herbicides labeled for use in potatoes
Postemergence grass control
 Poast (sethoxydim)
 Select (clethodim)
 Lorox/Linex (linuron) east of Rocky Mts only
“Burndown” - labeled for use after planting but
before potatoes emerge
 Roundup and others (glyphosate)
 Gramoxone and others (paraquat)
 Aim (carfentrazone)
Integrated Weed Management in Potatoes
Herbicides labeled for use in potatoes
Tank-mixing herbicides with different modes of action is
highly recommended
 Always read and follow the label
 Know potato varietal sensitivities
 Match each field’s weed spectrum with
appropriate herbicides
 Use appropriate rates, application methods,
incorporation methods
 Apply at optimum weed growth stage
 Understand carryover potential/follow-crop
plant-back intervals
Integrated Weed Management in Potatoes
Herbicides labeled for use in potatoes
Herbicides labeled for use in potatoes are
“safe” to potatoes mainly because of
selectivity which is due to:
 Metabolic or biochemical crop resistance
• Injury can still occur if potato plant growth
is slowed resulting in slow metabolism
• Plant growth can be slowed because of
stress from adverse weather conditions,
drought, insect/disease/nematode
infestation, etc.
Integrated Weed Management in Potatoes
Herbicides labeled for use in potatoes
Herbicides labeled for use in potatoes can
also be “safe” to potatoes due to:
 Application timing
 Rooting depth
 Selective placement
------------- Label specifics ------------
Matrix (rimsulfuron)
Group 2: ALS inhibitor – sulfonylurea (S.U.)
• PRE and/or POST
• Ground, chemigated, aerial
• 1 to 1.5 oz/A product
• PRE just after hilling, sprinkler incorporated
or chemigated
• POST before weeds are >1 inch
•Always use and adjuvant w/ Matrix
• PRE + POST or POST + POST
• 2.5 oz/A limit per year
• Follow crop challenges!
------------- Weed control -------------
Matrix weed control
•
•
•
•
•
•
Hairy nightshade
pigweed sp.
barnyardgrass
henbit
common chickweed (POST)
shepherd’s purse (POST)
• Suppression of yellow nutsedge (POST)
• Does not control ALS inhibitor resistant
weeds
Does not control cutleaf nightshade
Hairy nightshade
Cutleaf nightshade
Matrix injury
POST application - cloudy conditions
Matrix Rotation Restrictions
Rotational crop restrictions
 Spring wheat, barley = 9 months*
 Sugar beets = 18 months
 Winter wheat = 4 months
*Seed potato application
 Seed production practices may mean
decreased irrigation amount and
frequency, time for Matrix breakdown
 Rotational crop plant-back intervals may
need to be extended to 18 months

------------- Label specifics ------------
Outlook (dimethenamid-p)
Group 15: seedling growth inhibitor
Chloroacetamide (same as Dual Magnum)
• PRE only
• Ground, chemigated, aerial
• PRE just after hilling, sprinkler incorporated or
chemigated
• Coarse textured soils
(sand, sandy loam, etc.)
• 12 to 18 oz/A product
• Medium to fine textured soils (loam, silty loam, etc.)
• 18 to 21 oz/A product
• Follow-crop 4 months to fall-seeded small
grains
------------- Weed control -------------
Outlook - weed control
•
•
•
•
•
•
Hairy nightshade
pigweed sp.
barnyardgrass
Powell amaranth
mayweed chamomile
yellow nutsedge
•Need highest rate for a given soil texture
• Must have a tank-mix partner with Outlook
for common lambsquarters control
------------- Label specifics ------------
Chateau (flumioxazin)
Group 14: Protoporphyrinigen Oxidase (PPO)
Inhibitor – chlorophyll production
• PRE only
•1.5 oz/A product
• Ground, chemigated, aerial
• PRE just after hilling, sprinkler incorporated or
chemigated
• TARGETS HAIRY NIGHTSHADE
• Label states 2 inches settled soil covering any
vegetative portion of the sprouting potato
------------- Label specifics ------------
Eptam (EPTC)
Group 8 herbicide: lipid synthesis and weed seedling
inhibitor; inhibits cell division and elongation
• Can apply PPI 3.5 to 9 pt/A
• Ground-apply and incorporate same day
• Use minimum 5 pt/A for hairy nightshade control
• PRE 3.5 to 9 pt/A product or early POST 3.5
to 7 pt/A product
• Ground or chemigated
• PRE just after hilling, sprinkler incorporated or
chemigated
• PRE + EPOST sequential applications allowed
• 14 pt/A product limit per year
------------- weed control ------------
Eptam – weed control
• Does not control emerged
weeds
• Nightshade sp.
• annual bluegrass
• barnyardgrass
• yellow nutsedge
•Need the higher rates
• common chickweed
• pigweed sp.
Eptam (cont.)

Volatile – incorporation is key to
effectiveness especially on wet soils





Incorporation ½ hour on dry soils = 18% loss
Incorporation ½ hour on wet soils = 50% loss
Mechanical = top 2-3”/chemigation = 3-4” depth
Avoid chemigating during hot windy conditions
Short-lived



14 DAT 50% degraded/28 DAP essentially gone
PPI - apply as close to planting as possible
Eptam lay-by/after hilling for late-season control
Eptam (cont.)

Enhanced biodegradation




Can occur with repeated Eptam use



Microbial population buildup resulting in rapid
breakdown
50% degradation normally 14-21 DAT
Enhanced biodegradation = 7 DAT
Multiple years/multiple applications per year
NE, ND occurrences
Not common in Idaho
Eptam injury
“cosmetic” injury can occur under cool/wet
conditions
Prowl H2O (pendimethalin)
Group 3: Microtubule assembly inhibitor




Does not control emerged weeds

Pre and post up to 6” potato size

There’s a rate range – 2.1 pt/A product recommended
Best if incorporated within 1 week after
application


Cell division /Seedling Growth Inhibitors
Dinitroaniline (DNA) family
Chemigation/sprinkler-incorporation
Follow crop restrictions

Sugar beets 12 months – plowing recommended
------------- weed control ------------
Prowl H2O weed control
•
•
•
•
Common lambsquarters
barnyardgrass
Powell amaranth
Pennsylvania smartweed
Dual Magnum or Stalwart
(s-metolachlor or metolachlor)
Group 15: seedling growth inhibitor


Does not control emerged weeds



Chloroacetamide
Apply PRE to both crop and weeds
Postemergence applications can cause injury
Controls: Yellow nutsedge, Powell
amaranth, redroot pigweed, barnyardgrass
s-metolachlor postemergence: potato injury
------------- Label specifics ------------
metribuzin (formerly Sencor)
Group 5: Photosytem II inhibitor






Triazine family
Flexible: PPI (ID only), Single PRE, single POST,
PRE+POST, POST+POST (ID, OR, WA only)
Chemigation or sprinkler-incorporation
Metribuzin can injure potatoes under stress
Apply POST after weather has been sunny for at
least 3 days and forecast is for at least 2 sunny
days
Moderate soil residual
------------- weed control ------------
metribuzin (formerly Sencor)







common lambsquarters
Shepherd’s purse
smartweed sp.
barnyardgrass
Does not control hairy nightshade and
triazine resistant weeds
Fair control of foxtail sp. and wild oat
Controls seedling weeds before or after
emergence – emerged weeds must be <1”
Weed Control with metribuzin alone or tank-mixed with Outlook
Metribuzin alone does
not control hairy
nightshade
Hairy nightshade, redroot pigweed,
common lambsquarters,
and green foxtail present in the
non-treated, weedy check
Trial was conducted at the Aberdeen
R&E Center. Herbicides were applied
PRE and sprinkler-incorporated w/in 24
hr by 0.5 inches irrigation water
Metribuzin +
Outlook
provided 100%
control of
weeds in plot
metribuzin (formerly Sencor)
Do not make applications on earlymaturing, smooth-skinned white- or redpotato varieties
 Varietal sensitivity

Shepody (white skinned) – very sensitive
 Yukon Gold (yellow) – moderately tolerant
 Chipeta (chipper) – tolerant
 Russet Burbank, Ranger Russet, Russet
Norkotah - tolerant

Metribuzin injury on potatoes
• Injury may first appear as
yellowing/chlorosis in the leaf
veins
• Metribuzin metabolism occurs
in the veins of the potato leaf,
hence, the chlorotic
appearance in that area if the
herbicide is not being
metabolized
• Eventually, the metribuzin
which has not been
metabolized can move beyond
the leaf veins resulting in a
spread of injury symptoms
outside the leaf veins
Metribuzin injury on potatoes
• In contrast, compounds produced when
metribuzin is metabolized cannot move past
the veins into the area between the veins due
to the nature of those compounds and the
plant transport mechanism
• A susceptible potato variety does not break
the herbicide down quickly enough or at all
before injury symptoms or even plant death
occurs
Metribuzin injury on potatoes
• Injury symptoms also can appear on a
metribuzin-tolerant variety due to plant stress
causing slowed plant growth resulting in
slowed metabolism
• Cloudy conditions just before or after foliar
application also may slow plant metabolism,
and in turn, cause injury symptoms to appear
– Once conditions improve, plant growth and metribuzin
metabolism resumes in the tolerant potato variety and
injury is no longer apparent.
Perennial Weed Control in Potatoes

Field bindweed – none



Canada thistle



suppression w/ Matrix
Control Fall after small grain harvest
Yellow nutsedge


cultivation temporarily reduces top growth
control Fall after small grain harvest
suppression w/ Dual Magnum, Outlook, or Matrix
Quackgrass

Suppression/control w/Eptam, Matrix,
Poast, or Select
Postemergence grass control
with Select or Poast
Group 1: ACCase inhibitors
 Always use a nonphytotoxic crop oil concentrate
with Select or Poast
 Controls most grasses
 The typical maximum grass size for Select or
Poast is less than 8 inches
 A “Rescue” application of Poast to grasses 8 to
12 inches tall is allowed in the Midwest, South,
and Northeast but NOT in the West!
Herbicide Resistance
Resistance occurs through the selection of
biotypes naturally tolerant/pre-adapted
existing in a susceptible population. The
herbicide provides the selection pressure.

the biotype has survival and/or
reproduction advantages in the herbicide
environment

when and where depends on many factors
such as the initial frequency and fitness of
the resistant biotype, herbicide history,
cultural practices
Development of a resistant weed population through herbicide selection
1
2
Herbicide sprayed on
weed population in a field
Some weed plants of a given species
already exist in that species population
susceptible
resistant
3
Repeat use of same
herbicide and/or mode of action
Resistant weed plants of a given species
survive and produce seed, susceptible plants
of that species do not survive
After repeated use of the
same herbicide and/or
mode of action, the resistant
weed plants have survived
and now dominate
the population
Metribuzin applied POST to susceptible redroot pigweed
Metribuzin applied POST to resistant redroot pigweed
Herbicide Resistance
Definitions


Herbicide resistance: the inherited ability
of a plant population to survive a herbicide
treatment to which the original population
was susceptible
Tolerance: the capacity of a plant to survive
a herbicide application at it’s use rate due to
a characteristic of the plant species - this
species was never susceptible to the
herbicide
Herbicide Resistance
Definitions



Mode of action (MOA): the sequence of
events in which a herbicide kills a weed
Site of action/Target site: the particular
plant function that is affected by the
herbicide - specific location(s) where the
herbicide has activity within the plant
Herbicide class/group: herbicides with
similar modes of action
Herbicide Classes - History




Industry reps, weed scientists in Canada,
Australia and the U.S. have been working on a
herbicide classification system based on mode of
action since 1989
PNW Bulletin 437 published in 1993 - revised
1999
Herbicide class required on Australian labels –
1994
Weed Science Society of America commissioned
drafting of a herbicide classification system –
1995 Revised 2003
 28 classes/groups
Herbicide Classes
Group 1: Acetyl CoA carboxylase (ACCase)
inhibitors

Achieve, Assure II, Axial, Discover Select,
Poast, Puma,
Group 2: Acetolactate synthase (ALS)
inhibitors
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Imi’s- Assert, Raptor, Arsenal
S.U.’s- Matrix, Express, Harmony Extra,
UpBeet, Maverick, Oust
Group 3: Microtubule assembly inhibitors

Dinitroanilines (DNA’s)- Prowl, Sonalan,
Treflan, Balan
Herbicide Classes
Group 4: Synthetic Auxins
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Phenoxy- 2,4-D, 2,4-DB, MCPA
Benzoic acid- Banvel, Clarity
Carboxylic acid- Curtail, Starane, Stinger,
Tordon
Quinaline carboxylic acid- Paramount
Group 5: Photosystem II inhibitors
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Triazine- metribuzin, Velpar
Uracils- Hyvar, Sinbar
Phenyl carbamate- Betamix,
Pyradazinone- Pyramin
Herbicide Classes
Group 9: EPSP synthase inhibitors
 Roundup
Group 10: Glutamine synthetase inhibition
 Liberty
Group 14: Protoporphyrinigen Oxidase (PPO)
Inhibitors
 Chateau, Aim
Herbicide Classes
Group 15: Chloroacetamides - Inhibits very longchain fatty acid (VLCFA)
 Dual Magnum, Outlook
Group 16: Unknown site of action
 Benzofuran- Nortron
Group 22: Photosystem I electron diverters
 Bipyridiliums- Gramoxone Max, Diquat,
Reglone
Knowing the mode of action/herbicide
class is the key to planning a
management strategy to reduce the
potential for resistant weeds
Herbicide Resistance
Management Strategies

Herbicide/Crop rotation

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Tank-mix with a different mode of action

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different MOA’s
different cultural practices
overlapping weed spectrum
economics
Cultivation / Integrated weed management
Keep complete herbicide/weed control
histories
Use clean, tested, tagged seed for all your
crops
Herbicide Resistance
Management Strategies


Competitive crop
Scout - before and after application

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use an appropriate herbicide, when
necessary
do something about escapes/shifts
Good application
Sanitation - prevent spread

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clean equipment before moving
screen irrigation water
The more diversity in weed control tools used,
the less risk of selecting resistant weeds.
All other possibilities for poor herbicide
performance should be ruled out before
considering the possibility of resistance
misapplication
environmental conditions
heavy weed pressure
skips
Grower “IF’ Questions



If the same herbicide or class of herbicides
has been used in the field for sequential/
several years
If the suspected resistant weed species has
been controlled effectively in the past
If weed control is good on all the other
labeled weed species
If the answers are “Yes”
then maybe resistance is involved
What to do...

If you suspect herbicide resistance:


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Do not respray the field with the same
herbicide or herbicide class - control the
weed with another means - do not allow
seed to mature
Report your suspicion to university
research/extension personnel/extension
educator/crop advisor
Collect plants or seed that can be used to
confirm resistance has developed
Herbicide Resistance
Management Strategies

You can prevent or delay the development of
resistant weeds in your potato cropping
system if you follow a good strategy


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
know your herbicide classes
rotate crops/herbicides, tank-mix different
MOA’s
Tank-mix herbicides with different MOA’s overlapping spectrum
use an integrated approach
Herbicide Resistance
Management Strategies
The most comprehensive resistant
weed management programs are
set up before herbicide-resistant
weeds become a problem
Weed Management in Potatoes
The topics covered today

Weed – Potato interference

Major problem weeds
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Integrated weed management
strategies for potatoes
Herbicide resistance management
Weed Management in Potatoes
PPS Chapter 13
CIS 1037 Matrix in Weed Management Systems for Potatoes
CIS 1126 Outlook Herbicide for Weed Control in Potatoes
CIS 1136 Chateau Herbicide for Use in Potatoes
CIS 1185 Weed Control and Potato Crop Safety with Metribuzin
Want .pdf files of potato extension bulletins?
www.cals.uidaho.edu/edCom


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
Online catalog
Click on Crop on the side menu
Click on Potato:
drop down list of all our Potato publications
phutch@uidaho.edu