Organic Weed Management

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Organic Weed Management
Alisha Rupple, University of Arkansas Heather
Friedrich, University of Arkansas
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Weeds Top Issue for Organic Farmers

• Successful Management Requires
• Multiple approaches
• Continual effort
• Knowledge of the biology of weeds species
• Reproduction, lifecycle, establishment annual,
  perennial, wandering perennial, broadleaf, grass
• Cornell Organic Weed Database, www.css.cornell.edu
  /WeedEco/WeedDatabase/index2.html

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Basic Weed Ecology

• Weeds are natures way of keeping bare ground
  covered and increasing biodiversity
• Dynamic system involving the interaction of
  weeds, crops, humans and environment
• Factors affecting weed ecology are identical to
  those affecting crop ecology
• Light, temperature, water, pH, nutrients, organic
  matter, insects and diseases, etc

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Impact of High Weed Pressure

• Compete with crops for nutrients, water, and
  light
• Reduced yields
• Lower crop quality
• Harbor pest insects and diseases
• Increase irrigation costs
• But, complete elimination of weeds is unnecessary
  

Crop yield
Weed numbers or size
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Multiple Prevention and Elimination Strategies

• Cultural
• Mechanical
• Biological
• Chemical (organically
• approved)

Many hammers approach. Liebman and Gallandt,
1997
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Organic weed management practices Crop
Rotations on Organic Farms, Mohler Johnson, 2009
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Cultural Strategies

• Buy quality crop seed with low/no weed seeds
  present
• Do not allow weeds to form seed
• Thoroughly compost (gt130F for 15 days) all
  manure and plant residues to ensure destruction
  of weed seed
• Stale seedbed technique
• Prepare soil for planting and bring weed seeds to
  the surface allow weeds to germinate, kill weeds
  with light tillage/minimal soil disruption. May
  be repeated. Plant main crop.

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Cultural Practices

• Improve crop competitiveness
• Improve soil tilth, aeration, and fertility to
  optimize crop growth
• Increase crop density through narrow
  row spacing and increased seeding
  rate
• Use transplants, rather than seed, when possible
• Plant at optimal soil temperatures to prevent
  slow germination of crop
• Choose competitive crop cultivars
• Manage fertility according to crop needs avoid
  excess application

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Cultural Practices

• Reduce weed numbers
• Mulch (wood chips, mow and blow, paper, living,
  plastic, etc)
• Use weed-suppressive cover crops
• Quick germinating, high biomass
• Field with high weed pressure may warrant full
  year of cover cropping and fallow to reduce weeds
• Crop rotations
• altering narrowly spaced crops with closely
  spaced crops, shallow rooted/deep rooted crops,
  cold/warm season crops
• Intercrop
• Clover underseeded in sweetcorn

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Mulch

• Prevent seeds from germinating by blocking light,
  can smother out some weeds
• Conserve water, minimal soil disruption
• Use local resources straw, fabric, wood,
  newspaper, plastic
• Be careful of weed seeds in straw or hay
• Avoid hay, unless you know its free of weeds
• Especially good for perennial systems
  blueberries, blackberries, flowers, trees
• Living mulches ie constant cover of clover on
  orchard floor

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Wood chips
Leaves
Shredded paper
Straw
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Cover Crops

• Smother weeds by out-competing for light, water,
  nutrients
• Release allelopathic chemicals that suppress weed
  germination
• May reduce weed emergence by 75-90
• e.g. sudan grass, buckwheat, annual rye grass,
  sesbania, many more

Field pea-oat-mustard cover crop
Managing Cover Crops Profitably, 3rd ed. SARE
www.sare.org/publications/covercrops/covercrops.pd
f crops profitably. 3rd ed. SARE
Red Clover
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Crop Rotations

• Weeds tend to infest crops with similar life
  cycles
• Change crop ecology shallow/deep roots,
  cold/warm season, row/drilled crops, foliage
  density, and heavy/light feeders
• Change cultural practices cultivation, mowing,
  fertilization, herbicide application, and
  planting/harvest dates

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10 Year Rotation SchemeAlex and Betsy Hitt,
Chapel Hill NC http//www.ssawg.org/hitt.html
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Physical and Mechanical Practices

• Mowing
• Prevents seeding
• Depletes storage reserves
• Better control for broadleaves
• Soil solarization
• Effective control of winter annuals
• Limited control of perennials
• Cost prohibitive on large acreages
• Avoid tillage deeper than 3 after solarization

• Hand weeding
• Cultivation
• Flaming

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Cultivation

• Should be shallow to lessen disturbance to weed
  seed bank
• Better for perennial and biennial control than
  annual weed control
• Exhaust root system by depleting storage reserves
• Requires 6-8 timely treatments in yr 1, then 3-5
  the following year

Wheel hoe
Thoroughly clean equipment before moving it
between fields to prevent weed transport
Various hoes
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Potential Downsides of Cultivation

• Exposes bare ground
• increased erosion,
• decreased biodiversity,
• speeds decomposition of OM,
• increases water run-off
• Major cause of soil compaction
• Cost expensive equipment, fuel
• Should not be done in wet conditions

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Use Cultivation Wisely

• USDA-ARS research showed organic methods can
  increase OM more than conventional no-till
• Teasdale et al., 2007. Potential Long-Term
  Benefits of No-Tillage and Organic Cropping
  Systems for Grain Production and Soil
  Improvement. Agron J. 991297-1305
• Negative effects of tillage may be offset by the
  use of cover crops and additions of organic
  matter (compost, manures, mulch, etc)
• Must still use caution to avoid negative effects
  of cultivation

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Type of Horticultural Cultivators

• Spyders
• Torsion weeders
• Spring hoe weeders
• Finger weeder
• Basket weeder
• Multiple-component weeder frame
• Brush weeder
• Rotary tilling cultivators
• Rear- or front-tine tillers
• Hand implements push-pull hoes, hand scrapers,
  etc

Sustainable Vegetable Production from Start-Up to
Market, Grubinger, 1999
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Other Cultivators
Sustainable Vegetable Production from Start-Up to
Market, Grubinger 1999, NRAES 104
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Flaming

• Intense heat sears the leaf, causing the cell sap
  to expand and disrupt cell walls
• seedlings are most susceptible
• Broadleaf weeds are more susceptible than grasses
• May be used in wet soil conditions
• VIDEO www.extension.org/pages/Video_Clip_Backpac
  k_Flame_Weeder_from_Vegetable_Farmers_and_their_We
  ed_Control_Machines

Sustainable Vegetable Production from Start-Up to
Market, Grubinger, 1999
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Uses for Flaming

• Stale seedbed technique
• Planting delayed after seed bed preparation
  (tillage, irrigation, etc)
• Flaming knockdowns flush of weed seedlings prior
  to planting
• Peak emergence technique
• Crop seeded promptly after seedbed preparation
• Just before crop germinates, flaming used to kill
  weed seedlings
• Good method for direct-seeded, slow-germinating
  crops
• Glass or plastic can be used as a
  crop-germination indicator crop grown under
  cover germinates 2-3 days before uncovered crop
  flaming should occur when crop germinates under
  cover
• Post-emergent flaming
• Emerged crops protected by directing flame away
  from crops, shielding the crop, or flaming at a
  time when crop stems are resistant to heat
• Older plants able to recover from heat damage,
  while young seedlings are killed

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Flaming Tips

• Bigger weeds and wet weeds are harder to kill
• Target weeds while seedlings up to 3 to 4 leaves
• Avoid flaming with morning dew
• Light drying winds and hot days increase
  effectiveness
• Avoid flame deflection by soil clods or excessive
  dust protect weeds
• Match equipment for your needs
• Save on fuel, time
• Make time for adjustments
• Burner placement, fuel pressure, tractor speed
• How much is enough?
• When you squeeze plant leaf between finger and
  thumb, want to see your thumb imprint cells
  have burst and weed will die/setback

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Biological Control Practices

• Insects may consume large numbers of weed seeds
  or feeding injury to plant or vector virus
• Thistle adult thistle-head weevil, Rhinocyllus
  conicus
• Multiflora rose rose rosette disease
  transmitted by fungi or a (mite)
• Selective grazing
• Sheep clean fields after harvest
• Weeder geese useful against grass weeds and in
  perennial systems

• Biofumigation
• Use of Brassica species (canola, Indian mustard)
  as cover crop or in rotation
• May be incorporated or left as residue
• Brassicas produce glucosinolates, which may by
  converted to cyanate compounds during
  decomposition
• Cyantes toxic to many bacteria, fungi, nematodes,
  insects, and germinating seeds

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Chemical Control

• Organic options
• Corn gluten meal (pre-emergent herbicide)
• Suppresses many common grasses and herbaceous
  weeds
• WeedBan and Corn Weed Blocker
• Look for non-gmo sources
• Commonly based on vinegar or lemon juice or clove
  oil ingredients (post-emergent burndown
  herbicide)
• Perennials may require multiple applications
• Corrodes metal sprayer parts
• Burnout, Bioganic, AllDown , MATRAN, and
  Weed Bye Bye
• Post-emergent chemicals are phytotoxic (burn
  plant tissue) use caution when applying in crops

Organic herbicide in an orchard
Cost can be decreased by knowing pattern of weed
distribution (spot treatment v. overall
application
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12 Steps to Sustainable Weed Management Mark
Schonbeck

• Pre-season Planning
• Step 1. Know the weeds on your farm.
• Step 2. Plan cropping systems to minimize open
  niches for weeds.
• Step 3. Keep the weeds guessing.
• Step 4. Design the cropping system and select
  tools for effective weed control.

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Preventive (Cultural) Practices

• Step 5. Grow vigorous, competitive crops.
• Step 6. Put the weeds out of work grow cover
  crops.
• Step 7. Manage the weed seedbank minimize
  deposits and maximize withdrawls.

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Control Tactics
Step 8. Knock the weeds out at critical times.
No-till organic farm Weed-free bed of
weed-sensitive onion crop.

• Step 9. Utilize biological processes to enhance
  weed control.
• Step 10. Bring existing weeds under control
  before planting weed-sensitive crops and
  long-term perennial crops.

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Enhancing and Fine-tuning the Weed Management
Strategy

• Step 11. Keep observing the weeds and adapt
  practices accordingly.
• Keep notes
• What is suitable for one crop may not be for
  another
• Step 12. Experiment and stay educated. Keep up on
  new developments and practices.
• Night time cultivation
• Soil solarization
• Others

Weed free bed of carrots
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Conclusion

• Using multiple approaches (many hammers) to
  manage weeds will yield greater impact than
  relying on a few practices.
• Develop a weed management strategy that is
  designed for the needs of your farm.

• Big Hammers
• Competitive crops
• Rotation
• Cover Crops
• Mulches
• Weed predators
• Livestock/grazers
• Cultivation tools
• Rollers/roller-crimper
• Flamers
• Growers Observation

• Little Hammers
• Solarization
• Organic herbicides
• Bioherbicides
• Soil microorganisms
• Crop-weed interactions

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Resources

• The Sustainable Weed Control Rag, Mark Schonbeck,
  e-Organic, www.extension.org/article/18529,
  www.extension.org/article/18539
• www.extension.org/article/18538
• Sustainable Vegetable Production from Start-up to
  Market, Grubinger, 1999. NRAES-104
• Crop rotation on Organic Farms A Planning
  Manual, Mohler and Johnson, 2009. NRAES-177
• Managing Cover Crops Profitably, 3rd ed. SARE
  www.sare.org/publications/covercrops/covercrops.pd
  f
• Michigan Field Crop Pest Ecology Management.
  Cavigelli et al. 2000, MSU Extension Bulletin
  E-2704
• Cornell Organic Weed Management Website,
  www.css.cornell.edu/WeedEco/WeedDatabase/index2.ht
  m l

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Acknowledgements

• This presentation address general organic
  production practices. It is to be to use in
  planning and conducting organic horticulture
  trainings. The presentation is part of project
  funded by a Southern SARE PDP titled Building
  Organic Agriculture Extension Training Capacity
  in the Southeast
• Project Collaborators
• Elena Garcia, University of Arkansas CESHeather
  Friedrich, University of ArkansasObadiah Njue,
  University of Arkansas at Pine BluffJeanine
  Davis, North Carolina State UniversityGeoff
  Zehnder, Clemson UniversityCharles Mitchell,
  Auburn UniversityRufina Ward, Alabama AM
  UniversityKen Ward, Alabama AM UniversityKaren
  Wynne, Alabama Sustainable Agriculture Network