Tri-State Organic IP Video Series
Indiana - Illinois - Ohio - Michigan
Session II - March 15, 2007
Organic Weed Management
Supported by USDA’s
NCR Sustainable Ag Research and Education Program and
Risk Management Agency
Purdue University is an Equal Opportunity/Equal Access institution.
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Self-report 2.5 CEU’s in Pest Management
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Purdue University is an Equal Opportunity/Equal Access institution.
Tri-State Organic IP Video Series
Indiana - Illinois - Ohio - Michigan
Future Sessions
Apr.19 Insect and Disease Control in Organic Vegetables
Sep.20 Organic Poultry Production
Nov.15 Introduction to Organic Markets and Certification
Register at www.conf.purdue.edu/VIDEO/
Supported by USDA’s
NCR Sustainable Ag Research and Education Program and
Risk Management Agency
Purdue University is an Equal Opportunity/Equal Access institution.
Simmons Family Farm
By
John Simmons
North Branch, Michigan
Soil Characteristics that
Influence Weed
Management
Stephen Weller
Department of Horticulture and
Landscape Architecture
Purdue University
West Lafayette, IN
Weed Management Talks Tonight
• Soil Characteristics that Influence
Weed Management – Steve Weller
• Cropping Practices that Influence Weed
Management – John Cardina
• Tools, Practices, and Materials for
Weed Management – John Masiunas
• All these topics are related but ‘Soil
Quality’ is the basis of good or bad
farming
Basis of Effective Weed
Management
• Integrated Weed Management
– Use of all available tools to mange weeds
in agricultural fields and integration of
these into an ecological approach to farm
management
• Basis of an effective farming system depends
on maintenance of a quality soil
• Soil quality affects soil factors that can affect
weed presence, abundance and type
• Weed management becomes more problematic
when soil is improperly maintained
Some Thoughts about Weeds
• Weeds are a symptom of a soil problem
• Weeds can give insight into soil
problems
• Knowledge of weed indicators can
allow modification of soil management
practices
• Soils when properly managed will grow
better crops and lessen negative
influences of weeds
Typical Pattern of Summer Annual
Weeds in a Spring Planted Crop
Many points in
the cycle where
weeds can be
Influenced
Soil factors can
influence all
of these
Soil Ecology
Soil Ecology dictates ecosystem processes:
1. Cycling of nutrients
- decomposition
- mineralization
- energy turnover
2. Biodiversity – plants, animals, microbes
The diversity and abundance of live in soil exceeds
that of any other ecosystem and can interact to
affect weed presence and abundance.
Organic Agriculture
“Alternative strategies for managing plant
growth and pest management”
Soil health (Quality) = Plant
health
• Strongly related to soil biology
• Soil “Organism”- the Living Soil
– Eats
– Breathes
– Circulates fluids and nutrients
– Reproduces itself
Ecological Perspective:
“Alternative strategies for managing plant
growth and Pests.”
Chemical
N-fixation
Weathering
Mycorrhizae
Mineralization
Biological
Humus
Formation
Soil mixing
Aggregation
Aeration
Physical
Ecological Perspective:
• Sustainable Agriculture demands a
holistic perspective:
Soil
Farmers
Water
Wildlife
Livestock
Crops
• Don’t treat the symptoms, manage
the cause!
Characteristics of Good Soil
High Organic Matter
 Good
exchange
of soil gases
 Good
movement
of water
 Good
tilth
for root
growth
Features of a “Quality” Soil
•
•
•
•
•
•
•
•
•
Soft and crumbly, few clods / no hardpan
Well drained and warms quickly in spring
Infiltration after heavy rains, little runoff
Resists erosion and nutrient loss
High populations of beneficial soil
organisms
High nutrient holding capacity
Crops respond to low inputs
High productivity
Free of harmful contaminants
Platy structure in surface soil resulting from compaction
Poor Soil Quality
• Compacted
• Poor Aeration
• Restricted Root
Growth
• Low Nutrient
Holding Capacity
• Low Organic Matter
• Lacks Soil
Organisms
Soil Factors Important in Weed
Management
• Chemical properties
– Fertility
• Amount and variation in types
• Application timing and Placement
–pH – acidity or alkalinity
–Allelopathy – presence of plant
or microbe produced chemicals
that influence plant growth
Fertility
Fertility
Fertility
Fertility
• Give crops the nutrients they need in
the right amounts when and where they
need them most
• Fertilize the crops not the weeds
• Fertility allows crops to grow faster
than the weeds
• Quality soil will help balance nutrient
availability – organic matter influence
pH Effects
Soil Factors Important in Weed
Management
• Physical properties
– Composition
• Sand, silt, clay and organic matter
– Moisture and water holding capacity
– Aggregate size
– Compaction
– Amount of disturbance
Soil Structure
• Relates to the clumping or aggregation
ability of the soil (sand, silt, clay) into
secondary clusters (peds)
Can be improved or destroyed by choice
and timing of agricultural practices
Granular Structure
Angular Blocky Structure
Soil Structure and Seed
Germination
Compaction
Examples:
Field Bindweed,
Buttercups,
Chamomile, cinquefoil,
Corn marigold,
Quackgrass, mustards,
Pennycress
Poor Soil Aeration due to Ponded Water
C
o
m
p
a
c
t
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o
n
Soybeans are dying due to poor soil aeration.
Southern Tippecanoe Co. 2002
L
a
c
k
o
f
s
u
r
f
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c
e
d
r
a
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n
a
g
e
Soil Tilth and Organic Matter
• Good Tilth = soils that are “friable” with no
crusting, excellent water penetration, and
good structure
• Good physical soil condition impacts:
– Tillage ease
– Seedbed quality
– Seedling emergence ease
– Deep root penetration
– Reduced water runoff
– Increased water holding capacity
• All relates to OM/Humus and soil
aggregation
Soil Organic Matter and
Humus
• Organic matter
– Dead organisms
– Plant matter
– Other organic matter in various stages of
decomposition
• Humus
– Dark colored organic matter in final stages of
decomposition - quite stable
• Serve as a reservoir of plant nutrients and
help build soil structure
Soil is “Living” not Inert
• View soil as a living organism containing
many types of “livestock”
• 1 acre of topsoil can contain:
–
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–
–
900 lbs. of earthworms
2,400 lbs. of fungi
1,500 lbs. of bacteria
133 lbs. of protozoa
900 lbs. of arthropods and algae
• They depend on organic matter for food
except algae, and all interact to release
nutrients, vitamins, amino acids, sugars,
antibiotics, gums and waxes.
Soil Factors Important in Weed
Management
• Soil Biological properties
• Organisms present in soil or on farm that can
affect weeds present and can predate weeds
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Birds
Mammals
Earthworms
Insects
Microbes
• All these organisms are influenced by
farming practices
Soil Microorganisms
Functions and Processes
• Decomposition of residues
• Release of plant nutrients
– Weathering of minerals
– Carbon dioxide
• Soil humus formation
• Improve soil structure
• N-Fixation
• Mycorrhizal relationships
• Plant pathogens
• Antibiotics produced
Factors Affecting Macro and
Micro Population in Soil
• Competition with other organisms
• Nutritional requirements
• Environmental Factors
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Depth
Season
pH
Moisture
Aeration
Texture
Structure
Temperature
Importance of
Earthworms
 Mix and aerate soil
 Decompose residues
 Increase nutrient availability
 Improve soil structure
 Increase infiltration of water
 Improve plant growth
 Eat
Soil Arthropods
• Sowbugs, millipedes, centipedes,
slugs, snails, springtails
• First decomposers which eat and shred
large particles of plant and animal
residues, weed seeds
• Waste is rich in plant nutrients
• Dung beetles - Recycle nutrients from
manure, reduce livestock intestinal
parasites
Soil Bacteria
• Make nutrients available for plants
• Release N, S, P, etc. from O.M.
• N fixation, nodulation – Rhizobium
• Solubilize nutrients from minerals acidifying
• Improve structure – foster aggregation
• Fight root disease (and can cause root
disease)
• Detoxify soils
• Smell of soil - (actinomycetes)
Soil Fungi
• Quick colonization and breakdown of
O.M.
• Release nutrients from soil minerals
• Release hormones and antibiotics
• Predators
• Colonize roots - mycorrhizae
– Aid in nutrient – water capture
– Aid in P uptake
Benefits of a “Healthy” Soil
• Balance of C and N and soil organisms
leads to:
– Rapid residue decomposition
– Granulation of soil into water stable aggregates
• Reduced erosion potential
– Decreased crusting and clodding
• Improved crop emergence and root growth/penetration
– Better water infiltration
– Improved internal drainage
– Increased water and nutrient holding
– Easier tillage and crop harvesting especially root crops
Sustainable Soil Management
Practices
• Soil organisms cycle nutrients and provide many other
benefits
• OM is the food for heterotrophic soil organisms
• Soil should be covered to protect it from erosion and
temperature extremes
• Tillage speeds the decomposition of OM – beneficial ???
• C:N ratio will effect rate of OM utilization and or
decomposition (> 25 /1 temporarily ties up N)
• Plowing can have + or - effects
• OM increases occur if additions exceed decomposition
• Soil fertility levels must be monitored and amended as
needed using manures, green cover crops, compost, and
mineral additives.
Weed Management Strategies Build
on Quality Soil Management
• Proper Soil Management to best match
crop demands to detriment of weeds
• Build good soil structure by using soil
organic amendments, cover crops,
catch crops and avoid tilling wet soils
• Reduce weed seedling emergence by
avoiding soil compaction
• Use allelopathy from cover crops
Weeds Common in Wet sites and
Poorly Drained Soils
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Alligatorweed
Annual bluegrass
Sedges
Barnyardgrass
Bittercress
Liverworts
Moneywort
Mosses,
Pennywort
Virginia buttonweed,
Improve tilth and drainage
Weeds Common in Compacted
Soil
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Annual bluegrass
Annual sedge
Broadleaf plantain
Speedwell
Goosegrass
Lespedeza
Prostrate knotweed
Spotted spurge
Weeds Common in DroughtProne Soils
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Bitter sneezeweed
Black medic
Broomsedge
Goosegrass
Lespedeza
Prostrate knotweed
Spotted knapweed
Spotted spurge
Yellow woodsorrel
Weeds found in Sites with High
or low Soil Nitrogen
• High N
– Annual bluegrass
– Common chickweed
• Low N
– Birdsfoot trefoil
– Black medic
– Broomsedge
– Corn Speedwell
– Hawkweed
– White clover
Weeds found in Acidic Soils
• Broomsedge
• Mosses
• Red sorrel
Weeds found in Shady Areas
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•
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Ground ivy
Japanese stiltgrass
Poison ivy
Violets
Virginia Creeper
Cropping Practices that
Influence Weed
Management
John Cardina
Ohio State University
cardina.2@osu.edu
Two goals:
1.Don’t let weeds emerge.
2.Don’t let escaped weeds
produce seeds.
Crop Rotation
Changing crop sequences to create an
unstable and inhospitable environment
for weed establishment and survival –
resource availability
allelopathic effects
soil disturbance
soil fertility
mechanical damage
X time
Grass crop
Mustard
Cover crop
Small grain
Grass crop
Mustard
Cover crop
Small grain
Smother seedlings
Allelopathy
Mixed root structure
Small grain
Cover crop
Mustard
Grass crop
Crop Rotation Impacts:
UNSTABLE CONDITIONS
Crop type – canopy shape, shading etc
Chemical environment –
fertility, allelopathy
Physical environment –
temperature, light, moisture
Timing of all field operations –
planting, tillage, cultivation, harvest etc.
Crop Competition
~ 50% of weed control
variety selection
resources – fertility, water
row spacing, seeding rate
soil management
Allelopathy
Cover Crops –
physical &
chemical
suppression
Hairy vetch
Rye
Grass-legume
Cover Crops –
- killed, mowed
- incorporated
- surface
residue
Mustard
Buckwheat
Crimson clover
Smother
Crops
Winter-pea
Red clover
Sorghumsudangrass
Oats
Mustard
smother crops
Corn
Soybean
Prevent weed emergence:
physical suppression
shade
allelopathy
Prevent weed seed production:
shade
Prevent weed emergence:
cover & smother crops
crop competition
Prevent weed seed production:
crop competition
Mechanical Weed Management
in Organic Crops
John Masiunas
University of Illinois
Mechanical Weed Management
in Organic Crops
• Necessary to understand in a system context
– What role does tillage play in your farming
system?
– What tillage tool is critical for your farming
system?
• Tillage or lack of tillage affects vertical and
horizontal distribution of weed seed and
vegetative propagules
Tillage and cultivation
• Timing and weed size are critical
• Tilling in fall can eliminate winter annuals
and biennials along with injuring perennials
• Spring tilling can eliminate first flush of
summer annuals
• Most effective methods are burial to ½ inch
or cutting at soil surface
Tillage and selectivity
• Selectivity is the ratio between weed control and
crop injury
• Selectivity greatest when crops differ from weeds
in:
– Growth habitat
– Emergence time
– Maturity time
• Weeds with short emergence period better
controlled than those with longer emergence
period
Tillage and cultivation
• Vary your tillage and cultivation tools to fit the
situation
• Cultivation is best done when weeds are small
• Shallow tilling when weeds are in the white thread
stage will avoid bringing up weed seed
• Burial versus uprooting versus cutting
– Burial works best for small weeds especially in the crop
row
– Burial best done when crop is larger than the weed
– If burying small weeds soil must be dry
Tillage and cultivation
• Burial versus uprooting versus cutting
– Aim of uprooting is to eliminate soil-root
contact
– Uprooting weeds works best when the soil is
damp
– Remove as much grass roots as possible
because growing point is near soil surface
Tillage and cultivation
• Burial versus uprooting versus cutting
– Slicing or cutting can effectively destroy shootroot connection
– Best done when soil is dry
– Some hoes such as stirrup hoe are designed to
be pulled over soil surface to cut off weeds
– Some weeds such as purslane and crabgrass
will reroot
Stale seedbed
• Soil tilled early
– Encourages early weed flushes
• Delay cropping until main flush of weed
emergence has passed
• Emerged weeds killed with shallow tillage,
flaming, or organic herbicides
– Do not till below ¼ to ½ inch
Blind tillage
• Shallow tillage of entire field after crop seeded
• Stirs soil above level of crop seed placement
– Causes desiccation and death of tiny germinating seed
• Most effective when soil fairly dry and weather
warm
• Provides the crop after emergence about a 10-day
weed free period
• Examples: rotary hoes, flex-tine harrows, chain
link harrows
Example 1: Rotary hoe
• Rotary hoes designed
for low or high residue
fields
• Can be used PRE or
POST as long as crop
more deeply rooted
than weed
Rotary hoe
• Advantages
– Rapid to use
• Disadvantages
– Large seed crops only
– Don’t hoe bean crops
in crook stage
– Will not kill green
weeds
Example 2: Flex-tine harrows
• Used broadcast over and between crop rows
• Most efficient when weeds are in white
thread or cotyledon stage
• Rely on differences in emergence and
rooting depth of crop versus weed
• Small seeded weeds best control
Flex-tine Harrows
• Advantage
– Operated at fast speed
– Do not require much
modification
– Break soil crusts
– Sections over crop row
can be lifted to avoid
injury
Flex-tine Harrows
• Disadvantages
– Primary action of postemergence harrowing is weed
burial
• Need to cover 1 to 1.5 inches
– Cultivation timing is critical
• Does not control grasses at any stage
• Only controls broadleaves less than 4 leaves
– Must be integrated with more aggressive cultivator
– Can reduce stand when used before crop well-rooted
Between-row cultivation
• Should not be primary weed control
• Selectivity can be low
• Implement when weeds one inch tall and
crop large enough to not be covered by dirt
• Usually requires more than one pass
• Examples: finger weeders, brush hoe,
spyders + tension weeders
Finger Weeder
• In row weed control
• Three pairs of grounddriven rotating fingers
– Front two pairs push soil
and uproot weeds away
from row
– Rear pair pushes soil into
row covering missed weeds
• Finger wheels tilted
downward
• Slow speeds and adjusted
so very near crop row
Finger Weeder
• Advantages
– Excellent in-row weed control
– Lightweight tool can be used with small tractor
• Disadvantages
– Timing critical – very small weeds (up to 1 inch), crop
must have sufficient stem strength
– Between-row weed control poor
– Slow, precise tillage is necessary
– Manufacturer: Buddingh Weeder Co.
7015 Hammond Ave., Dutton, MI 49316
Phone: (616) 698-8613
Brush Hoe
• PTO-driven plastic bristles
rotate on horizontal plane,
ripping weeds from soil
• Very aggressive
– Shields above soil to protect
crop row
– Operator on rear seat
required to steer shields
over crop row
Source: European Weed Research Society
Brush Hoe
• Advantages
– Can control weeds up
to ten inches tall
– Effective on slightly
moist soils
– Soil passing under
shields smoothes
weeds in crop row
– Dust layer from
brushing delays new
weed germination
Brush Hoe
• Disadvantages
– Requires two operators
– Cultivated crops must have same spacing
– Implement is costly
• Manufacturer
– Baertschi FOBRO, 1715 Airpark, Grand
Haven, MI 49417, Phone: (617) 847-0300, Fax:
(616) 842-1768
Summary
• Integrate mechanical weed management
with farm goals and systems
• Maximize selectivity
• Minimize weeds emerging with crop
through blind tillage
• Do not use cultivation as primary weed
management method
Questions
Email: ipevents@purdue.edu
Dale Rhoads
Rhoads Farm
Nashville, Indiana
Small Short
Season Crops
Salad Green,
Beets, Carrots
Sterile Seedbed
Short Season
Bare Ground
Lettuce
Transplant into Sterile
Seedbed,
Hand Weed
Long Season
Bare Ground
Corn, Tomato, Squash
Sterile Seed & Hand
Long Season
Transplanted Crops
Basil, Kale, Chard
Sterile, Straw or
Sawdust Mulch
Small Short Season
Crops
Salad Green, Beets,
Carrots
Sterile Seedbed
SAME
Short Season
Bare Ground
Lettuce
Transplant into Sterile
Seedbed,
Hand Weed
IN KILLED COVER
Long Season
Transplanted Crops
Basil, Kale, Chard
Sterile, Straw or
Sawdust Mulch
EARLY IN WINTER KILL
COVER, LATE-CR
Long Season
Bare Ground
Corn, Tomato, Squash
Sterile Seed & Hand
EARLY IN W.KILLED
COVER, LATE IN CRIMPED
COVER
Weed Management
Strategies
Lily Lake Organic Farm
Maple Park, IL
Dave Campbell
Transition Steps
• Emphasis on growing alfalfa / grass hay
• Strong horse hay market
• Erosion concerns
• Major weed issues
– First 3 – 5 years of transition
Benefits of Growing Legumes
• Root systems increase infiltration of air
and water into the soil
• Tap roots break through soil hardpan
allowing access to nutrients
Benefits of Growing Grass
• Rapid spring growth competes well with
weeds
• Best crop to plant for erosion control
• Fibrous roots reduce frost heaving of
alfalfa that is seeded with grass
Concerns About Raising Hay
• Best scenario – farm should contain
livestock
• Soil test at least every 3 years if no livestock
manure is applied to farm
• First choice – plant hay to fields with
highest potassium levels
Rotation at LLOF
• Year 1
Oats or Winter Wheat / Red Clover
• Year 2
Corn
• Year 3
Soybeans
Year 1 Oats or Winter Wheat /
Red Clover
• Fall seeded wheat
• Frost seed medium red clover in March
OR
• Spring seeded oats
• Seed red clover with oats
Year 1 Oats or Winter Wheat /
Red Clover
• Mow bad weed patches
• Hoe out or cut thistles
• Run straw through straw chopper
• Clip weeds in early September
• Chisel plow in late fall
General Tips on Weed Control
in Oats and Wheat
• Sow as early as possible, especially oats
• Increase seeding rates a little higher then
conventional rates
– Especially for high test weight oats
• May need to use a rotary hoe or tine weeder if
early weed growth is heavy
• Use clean seed only
Year 2 - Corn
• First pass – Field cultivator
– Till in the moderate to shallow range
• Second pass – Field cultivator
– Till in the shallow range
• Plant immediately after last tillage pass
• Don’t plant until soil temperatures have
warmed up
Year 3 - Soybeans
• Disk corn stalks in late April
– Early germinating weeds are killed off by
disking
• Moldboard plow after next weed flush
– Plowing buries many weed seeds
Year 3 - Soybeans
• Field is disked or field cultivated with
drag harrow attached
• Ground is field cultivated immediately
before planting beans to eradicate weeds
• Don’t plant until soil temperatures have
warmed up
Year 3 – Soybeans – After Harvest
• Disk down ridges to level field
• Lightly field cultivate with narrow shank
cultivator
• Sow winter wheat
• Drag field to cover exposed wheat
• Don’t do any fall tillage if sowing oats the
following spring
Rotary Hoeing Corn or Soybeans
• First hoeing to take place 3-5 days after
last tillage pass
• Adjust tractor speed and hoeing depth
when entering a new field
• Second hoeing to take place 3-5 days
after first hoeing
Row Crop Cultivation:
Corn or Soybeans
• Usually cultivate 3 times
• Cultivate with Buffalo cultivator
• Disk hillers are used
• Cultivision mirror is used
General Tips on Weed Control
in Corn & Soybeans
• Wait until soil warms up and dries out
before tilling and planting
• Don’t plant right before a heavy rain is
forecasted
• Destroy crop when weeds have overtaken
it
• Timing is everything!
General Tips on Weed Control
in Corn & Soybeans
• Use clean seed only
• Plant a little heavier than intended to
allow for loss of plants if needing to
rotary hoe aggressively
• Don’t take on a full-time job
Suppressing Canada Thistle
• Field cultivate every 2-3 weeks in the
spring time before crop is planted
• Mow thistles around entire farm before
seed head opens
• Talk with neighbors and/or local
authorities if problem is off the farm
Suppressing Canada Thistle
Smother and Starve Approach
• Sow alfalfa or grass for 3 years or more
• Sow buckwheat in a light to moderate infested
field
• Sow sorghum sudan grass in a moderate to
heavy infested field
Questions
Email: ipevents@purdue.edu