Integrated Weed Control
Strategies in Organic Farming
Jim Shrefler, OSU / WWAREC
Charles Webber, USDA / ARS
Warren Roberts, OSU / WWAREC
Merritt Taylor, OSU / WWAREC
“Lane Agricultural Center”
Cooperators / Collaborators
OSU Scientists, Specialists
USDA Scientists
Growers
Noble Foundation
Kerr Center
While On The Soapbox …
Why do we want to do this?
What are the problems with nonorganic?
– Are we irrationally disregarding
valuable technology?
Will organics be problem free?
Can exploration of organics lead to
conceptually new ideas?
What will the bottom-line be …..
– Should we consider multi-generation
sustainability?
Weed Control For Organics
- Presentation Emphasis Yes - Crops
– Fruits
– Vegetables
– Herbs
– Row Crops
No - Other Areas
– Forages
– Turf
– Ornamentals
What is a Weed?
“Plant whose virtues are yet
to be discovered”
“A plant out of place”
Regardless, whether wild or
cultivated, extraneous plants
in a crop can reduce yield,
quality and production cost
General Management Factors
Exclusion
Elimination
Prevent
Establishment
Removal
Amelioration
General Management Factors
- Exclusion Field selection
Prevent new weedy
species additions
General Management Factors
- Elimination Prevent weed build-up
Destroy propagules
– Solarization
– Fumigation
Eradication – For
minor infestations of
certain weeds
General Management Factors
- Prevent Establishment Herbicides
Cultivation
Cover crops
Grazing
Mulches
– organic and synthetic
General Management Factors
- Removal Mechanical
Chemical
Physical
– flame
– steam
General Management Factors
- Amelioration Crop Selection
– crops that tolerate weeds
– crops that enable control
of weeds
Give crop an edge
– transplants
– planting date
So, what can we do
under the constraints of
organics?
Weed Management for Organics
- Exclusion Field selection
– a good choice
– knowledge needed of sites
– usefulness depends on available
certified land
Prevent weed additions
– critical for Organics
– “bring-ins” may contain weeds
Organic mulches
Raw manures
Weed Management for Organics
- Elimination Prevent weed build-up
– timely cultivation, tillage
– purposeful plantings – don’t let weeds
take over
Weed population reduction
– perennial management through
grazing
– fallow / tillage cycles
– solarization
– fumigants???
Weed Management for Organics
- Prevent Establishment Preemergence “herbicides”
– corn gluten meal, mustard meal
Timely cultivation
Stale seedbeds
Cover crop management
– Species important: e.g. rye
– Crop sequence (more detail later)
Grazing
Mulches
– organic and synthetic
Weed Management for Organics
- Weed Removal –
“Stop ‘em in their tracks”
Mechanical – cultivation
– keep it shallow
–minimize injury to the crop
–Improve the root zone
Manual
– choose easy-to-use tools
Weed Management for Organics
- Weed Removal (cont.)–
“Stop ‘em in their tracks”
Chemical: vinegar, pelargonate, etc.
– currently just contact activity
– good foliage cover needed
Physical: energy consumers!
– flame
special equipment, directed flame
best for small, annual weeds
– steam
Weed Management for Organics
- Amelioration Crop Selection
– use crops that tolerate weeds
rapid growth, dense canopy
– crops that allow weed control
sweet corn – easily cultivated
Give crop an edge
– plant date
– transplants
Specific Examples of Tactics
Cover crop management
Preemergence “herbicide”
“Burn down” chemicals
Cover Crop Management
Cereal Rye a classic example
Effective due to
– Biochemical constituents
– Biomass
Management involves
– Coordination of rye growth with crop
plant date:
– Rye destruction: rolling?, tillage?
– Crop planting method
Preemergence “Herbicides”
Bioherbicides
Corn Gluten Meal
– Makeup: 9% nitrogen (fertilizer?)
– Available as powder, granule, pellet
Weed control properties
– Certain peptides toxic to germinating
seeds
– Works best under drying soil
conditions
– Apply to surface or mix very shallowly
Burn-down Chemicals
Pelargonic acid is a leading option
– Also called nonanoic acid & pelargonate
– Kills living plant tissue within hours
– Contact action not systemic
– Ammonium formulation for organic use
Control
– Grasses: Small & before tillering is best
– Broadleafs: varies with species
– No crop selectivity