Organic Weed Management

Alisha Rupple, University of ArkansasHeather Friedrich, University of Arkansas

Weeds: Top Issue for Organic Farmers

Successful Management Requires Multiple approachesContinual effortKnowledge of the biology of weeds species

Reproduction, lifecycle, establishment annual, perennial, wandering perennial, broadleaf, grassCornell Organic Weed Database, www.css.cornell.edu/WeedEco/WeedDatabase/index2.html

Basic Weed Ecology

Weeds are nature’s way of keeping bare ground covered and increasing biodiversityDynamic system involving the interaction of weeds, crops, humans and environmentFactors affecting weed ecology are identical to those affecting crop ecology:

Light, temperature, water, pH, nutrients, organic matter, insects and diseases, etc

Weed

Humans

Natural environment

Crop

Impact of High Weed Pressure

Compete with crops for nutrients, water, and lightReduced yieldsLower crop qualityHarbor pest insects and diseasesIncrease irrigation costsBut, complete elimination of weeds is unnecessary

Weed numbers or size

Cro

p yi

eld

Multiple Prevention and Elimination Strategies

CulturalMechanicalBiologicalChemical (organically

approved)

“Many hammers approach.”Liebman and Gallandt, 1997

“Organic weed management practices” Crop Rotations on Organic Farms, Mohler & Johnson, 2009

Practice Effect

Tillage Kills growing weeds; damages perennial roots & rhizomes; buries seeds too deeply to emerge; brings weed seeds to surface.

Post-planting cultivation Removes weeds from the crop.

Stale seedbed Flushes weeds from the soil before planting.

Organic fertility sources Favor crops over faster-growing weeds due to slow release of nutrients.

Drip irrigation Directs water to the crops rather than to weeds.

Mulch Smothers weeds: delays emergence of weeds

Using transplants Competitive advantage to crop

Competitive cultivars Improves competitive ability of crop against weeds.

Increase plant density Suppress weeds by shading

Rapid cleanup after harvest

Prevents seed set by residual weeds.

Cover crops Suppress weeds, improves soil health

Cultural Strategies

Buy quality crop seed with low/no weed seeds presentDo not allow weeds to form seedThoroughly compost (>130°F for ≥15 days) all manure and plant residues to ensure destruction of weed seedStale 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.

Cultural Practices

Improve crop competitiveness

Improve soil tilth, aeration, and fertility to optimize crop growthIncrease crop density through narrow row spacing and increased seeding rate Use transplants, rather than seed, when possiblePlant at optimal soil temperatures to prevent slow germination of cropChoose competitive crop cultivarsManage fertility according to crop needs; avoid excess application

Cultural Practices

Reduce weed numbersMulch (wood chips, mow and blow, paper, living, plastic, etc)Use weed-suppressive cover crops

Quick germinating, high biomassField with high weed pressure may warrant full year of cover cropping and fallow to reduce weeds

Crop rotationsaltering narrowly spaced crops with closely spaced crops, shallow rooted/deep rooted crops, cold/warm season crops

Intercrop Clover underseeded in sweetcorn

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

Shredded paper

Straw

LeavesWood chips

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

Red CloverManaging Cover Crops Profitably, 3rd ed. SARE www.sare.org/publications/covercrops/covercrops.pdf crops profitably. 3rd ed. SARE

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 feedersChange cultural practices: cultivation, mowing, fertilization, herbicide application, and planting/harvest dates

10 Year Rotation SchemeAlex and Betsy Hitt, Chapel Hill NC;

http://www.ssawg.org/hitt.htmlYR

Spring Summer Fall

1 Tomatos & leeks Oat-crimson cl

2 Flowers-cool seas. Sudangrass-soyb.

Oat-crimson cl.

3 Spring lettuce Flowers, summer

Rye-hairy vetch

4 Squash Fall planted flowers5 Flowers-

overwinteredSudangrass-soyb.

Rye-hairy vetch

6 Peppers Wheat-crimson cl7 Flowers -summer Oat-crimson clover8 Mixed spring veg cowpeas Fall planted flowers9 Flowers-

overwinteredSudangrass-soyb.

Oat-crimson clover

10

Flowers-summer Wheat-hairy vetch

Physical and Mechanical Practices

MowingPrevents seedingDepletes storage reserves Better control for broadleaves

Soil solarizationEffective control of winter annualsLimited control of perennialsCost prohibitive on large acreagesAvoid tillage deeper than 3” after solarization

Hand weeding

Cultivation

Flaming

CultivationShould be shallow to lessen disturbance to weed seed bankBetter for perennial and biennial control than annual weed control

Exhaust root system by depleting storage reservesRequires 6-8 timely treatments in yr 1, then 3-5 the following year

Thoroughly clean equipment before moving it between fields to prevent weed transport

Wheel hoe

Various hoes

Potential Downsides of Cultivation

Exposes bare ground: increased erosion, decreased biodiversity, speeds decomposition of OM, increases water run-off

Major cause of soil compactionCost: expensive equipment, fuelShould not be done in wet conditions

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. 99:1297-1305

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

Type of Horticultural Cultivators

Spyders™Torsion weedersSpring hoe weedersFinger weederBasket weederMultiple-component weeder frameBrush weederRotary tilling cultivatorsRear- or front-tine tillersHand implements: push-pull hoes, hand scrapers, etc

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

Other CultivatorsSustainable Vegetable Production from Start-Up to Market, Grubinger 1999, NRAES 104

Flaming

Intense heat sears the leaf, causing the cell sap to expand and disrupt cell wallsseedlings are most susceptible Broadleaf weeds are more susceptible than grassesMay be used in wet soil conditions

VIDEO: www.extension.org/pages/Video_Clip:_Backpack_Flame_Weeder_from_Vegetable_Farmers_and_their_Weed_Control_Machines

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

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 preparationJust before crop germinates, flaming used to kill weed seedlingsGood method for direct-seeded, slow-germinating cropsGlass 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 heatOlder plants able to recover from heat damage, while young seedlings are killed

Flaming Tips

Bigger weeds and wet weeds are harder to killTarget weeds while seedlings up to 3 to 4 leavesAvoid flaming with morning dew

Light drying winds and hot days increase effectiveness

Avoid flame deflection by soil clods or excessive dust = protect weedsMatch equipment for your needs

Save on fuel, timeMake time for adjustments

Burner placement, fuel pressure, tractor speedHow 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

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 conicusMultiflora rose & rose rosette disease transmitted by fungi or a (mite)

Selective grazingSheep: clean fields after harvestWeeder geese: useful against grass weeds and in perennial systems

BiofumigationUse of Brassica species (canola, Indian mustard) as cover crop or in rotationMay be incorporated or left as residueBrassicas produce glucosinolates, which may by converted to cyanate compounds during decompositionCyantes toxic to many bacteria, fungi, nematodes, insects, and germinating seeds

Chemical Control

Organic optionsCorn 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 applicationsCorrodes metal sprayer partsBurnout™, Bioganic™, AllDown ™, MATRAN™, and Weed Bye Bye™

• Post-emergent chemicals are phytotoxic (burn plant tissue); use caution when applying in cropsCost can be decreased by knowing pattern of weed distribution (spot

treatment v. overall application

Organic herbicide in an orchard

12 Steps to Sustainable Weed Management – Mark Schonbeck

Pre-season PlanningStep 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.

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.

Control Tactics

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.

Step 8. Knock the weeds out at critical times.

No-till organic farm; Weed-free bed of weed-sensitive onion crop.

Enhancing and Fine-tuning the Weed Management Strategy

Step 11. Keep observing the weeds and adapt practices accordingly.

Keep notesWhat 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 cultivationSoil solarizationOthers…

Weed free bed of carrots

ConclusionUsing 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

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-104Crop 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.pdf 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.htm l

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 CES

Heather Friedrich, University of ArkansasObadiah Njue, University of Arkansas at Pine BluffJeanine Davis, North Carolina State UniversityGeoff Zehnder, Clemson UniversityCharles Mitchell, Auburn UniversityRufina Ward, Alabama A&M UniversityKen Ward, Alabama A&M UniversityKaren Wynne, Alabama Sustainable Agriculture Network