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Organic weed management
- 1. Organic Weed Management Alisha Rupple, University of Arkansas Heather Friedrich, University of Arkansas
- 2. 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
- 3. Basic Weed Ecology Weeds are nature’s 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 Weed Humans Natural environment Crop
- 4. 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 Weed numbers or size
- 5. Multiple Prevention and Elimination Strategies Cultural Mechanical Biological Chemical (organically approved) “Many hammers approach.” Liebman and Gallandt, 1997
- 6. “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
- 7. Cultural Strategies Buy quality crop seed with low/no weed seeds present Do not allow weeds to form seed Thoroughly compost (>130°F 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.
- 8. 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
- 9. 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
- 10. 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
- 12. 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 Clover Managing Cover Crops Profitably, 3rd ed. SARE www.sare.org/publications/covercrops/covercrops.pdf crops profitably. 3rd ed. SARE
- 13. 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
- 14. 10 Year Rotation Scheme Alex and Betsy Hitt, Chapel Hill NC; http://www.ssawg.org/hitt.html Y R 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 flowers 5 Flowers-overwintered Sudangrass-soyb. Rye-hairy vetch 6 Peppers Wheat-crimson cl 7 Flowers -summer Oat-crimson clover 8 Mixed spring veg cowpeas Fall planted flowers 9 Flowers-overwintered Sudangrass-soyb. Oat-crimson clover 10 Flowers-summer Wheat-hairy vetch
- 15. 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
- 16. 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 Thoroughly clean equipment before moving it between fields to prevent weed transport Wheel hoe Various hoes
- 17. 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
- 18. 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
- 19. 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
- 20. Other Cultivators Sustainable Vegetable Production from Start-Up to Market, Grubinger 1999, NRAES 104
- 21. 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:_Backpack_Flame_Weed er_from_Vegetable_Farmers_an d_their_Weed_Control_Machine s Sustainable Vegetable Production from Start-Up to Market, Grubinger, 1999
- 22. 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
- 23. 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
- 24. 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
- 25. 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 Cost can be decreased by knowing pattern of weed distribution (spot treatment v. overall application Organic herbicide in an orchard
- 26. 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.
- 27. 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.
- 28. 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.
- 29. 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
- 30. 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
- 31. 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.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
- 32. 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 Arkansas Obadiah Njue, University of Arkansas at Pine Bluff Jeanine Davis, North Carolina State University Geoff Zehnder, Clemson University Charles Mitchell, Auburn University Rufina Ward, Alabama A&M University Ken Ward, Alabama A&M University Karen Wynne, Alabama Sustainable Agriculture Network
Hinweis der Redaktion
- Weed management is a top issue for most organic growers. It requires continual effort using multiple approaches we’ll cover in this presentation. Biological knowledge of the weed species working with can be essential for success. Knowing what type of weed it is, how it reproduces and it most vulnerable period are critical information to managing the species. The Cornell University organic weed database is a useful resource that provides this type of information as well as management practices for specific weeds.
- Weeds compete with crops for water, nutrients and sunlight. In high enough pressure weeds can reduce yields, reduce crop quality, increase irrigation needs and harbor insects (both beneficial and pestiferous) and diseases. Complete elimination of weeds is unnecessary, as they can protect the soil surface from heavy rain, add organic matter, help to recycle nutrients, provide habitat for beneficial insects and other impacts.
- Employing various strategies or “many hammers” are most effective for maintaining adequate weed control. These include cultural, mechanical, biological and chemical practices. Liebman and Gallandt. 2006. Many little hammers: ecological approaches for management of crop-weed interactios. In L.E. Jackson, 3d., Ecology in Agriculture, pp 291-343. Academic Press, San Diego CA
- Table 3.6 from Crop Rotations on Organic Farms: A planning manual. NRAES-177 This table summarizes the effect of various cultural and mechanical practices for weed management
- Note picture – these lettuce transplants have been in the ground for a few weeks; they are planted relatively close together, they are beginning to shade the ground, you can see the drip tape – watering the plants, not the weeds,
- Weed article
- A good resource for cover crops: Managing Cover Crops Profitably, 3rd ed. SARE www.sare.org/publications/covercrops/covercrops.pdf crops profitably. 3rd ed. SARE
- Note the frequency of cover crops in their rotation
- Keys to good solarization: work up soil to an even level surface removing big clods and rocks; lay thin plastic sheeting <3mm as close to the ground as possible, burying edges of plastic; use irrigation – wet soil conducts heat better than dry soil, field should remain at 70% field capacity; leave in place for 4-8 weeks; avoid anything more than shallow tilling to avoid bringing up weed seeds from lower depths that were not killed by the heat.
- http://agron.scijournals.org/cgi/content/abstract/99/5/1297 Organic agriculture is often criticized for heavy use of cultivation for weed control. Long-term research has shown that by using cover crops and fertilizing with materials high in organic matter such as manure, organic methods can provide greater long term soil benefits compared to no-till production.
- Sustainable Vegetable Production from Start-Up to Market, Grubinger 1999, NRAES 104
- Sustainable Vegetable Production from Start-Up to Market, Grubinger 1999, NRAES 104
- Hot days and drying winds further dry out weeds, for maximum impact Avoid “burning” weeds; If weeds are black you are using too much fuel
- Biocontrol is specific to the species and works well for infestations of a particular weed and typically in situations where immediate results are not necessary. Biocontrol mechanisms usually take time for maximum effectiveness. Phyllocoptes fructiphilus has been shown to transmit rose rosette disease on young fast growing roses
- Organic herbicides are expensive and will not work as effectively as conventional herbicides. May be useful in smaller, localized areas for spot treatment. The organic herbicides work by burning the plant tissue (due to very low pH), therefore good coverage is needed. Works better on smaller weeds.
- The Sustainable Weed Control Rag. Mark Schonbeck. An excellent resource that provides a whole farm, systems approach. The document can be found on the Resources page of the website. These steps provide a framework, not a step by step process. The steps combine direct and indirect management practices, and in conjunction with another have an additive effect on weed control, providing greater impact. Step 1 – know the major, problematic weeds on your farm – make sure they are identified correctly. Research the lifecycle, growth, reproduction, etc and when it is most susceptible to control tactics. Step 2 – Plan your crop rotation to minimize niches for weeds to emerge such as the transition time when a main crop is finished and a cover crop is planted and emerges. Consider overseeding into main crop before it’s completely finished with harvest; when main crop is done, a cover crop is established. A no-till planting of veggies into a killed cover crop, inter cropping, living mulches or organic mulches also reduces the niche for most weeds to emerge. Step 3 – Keep the weeds guessing through a varied crop rotation with crops and cover crops of varied harvest dates, that required varied planting densities, methods of tillage, irrigation, fertilizers. All of these things will impact the type and population of weeds. See Mark’s handout for further details. Step 4 – match cultivation tool for the crop and row spacing to get the best in-row and between row control; also consider the weed.
- Step 5 – grow vigorous crops and varieties that outcompete weeds as much as possible. Crops that close their canopy (with appropriate planting density) shade the ground below, preventing sunlight from reaching the ground and preventing weeds from germinating. Other tips: use high quality seed, use transplants when appropriate, if direct seeding plant at soil temps suitable for rapid germination (different for each crop), choose crop cultivars that are locally adapted, feed and water the crop, not the weeds. Step 6. Weeds have a natural purpose to cover and protect bare soil. By planting cover crops, you select which plants you want to grow and benefit the soil, doing the natural job of weeds. See SARE Managing Cover Crops Profitably 3rd ed. Available online at www.sare.org/publications/covercrops/covercrops.pdf Step 7. Many weed seeds remain viable in the soil for many, many years. Many seeds are lost each year due to predation by insects, microbes and mice, however the seedbank can be replenished with inputs such as manure or compost fertilizers, mulches such as hay or straw, wildlife/birds, the movement of soil on equipment or even shoes. Effort should be made to minimize the numbers of weeds that go to seed (a primary source of seedbank renewal). Also, use clean inputs - compost manure to 140F for at least 3 days to kill seeds, know the source and quality of mulches used, clean equipment before moving it to another field. Remove seeds with the stale seedbed technique and encourage weed seed predation of beetles, cricket, mice – ie use cover crops and let critters glean before you work up or mow the harvested fields.
- Step 8. Each crop has a ‘critical weed free period’ where it must be kept free of weed competition to prevent yield loss/economic loss from occurring. For a crop like snap beans this is from emergence to full bloom, but for a crop like onions, its all season long. This table shows other crops, http://www.ncsu.edu/sustainable/IPM/weeds/table7_1.html. The most critical times for weed control throughout the season generally are: 1) at planting, 2) as flushes of weed seedlings are emerging 3) during the crops minimum weed free period, 4) when perennial weed reserves reach a low, 5) before the weeds for seeds or propagate. Step 9. biological control of weeds will likely never be as predominant as biological control in the insect world, even though advances have been made in “bioherbicides”. The examples of the multiflora rose and thistle in previous slides are two examples of biocontrol of invasive species. Even though biological products or agents play a minor role in weed management, biological processes play a significant role. These processes include herbivory, vectoring diseases, plant-soil-microorganism relationships that give competitive advantage to the crop and not the weed, allelopathy, and weed seed decomposition and decay. These elements are a natural part of a healthy, diversified organic ecosystem. Step 10. Preventative measures to get weeds under control before you plant a perennial crop such as berries, tree fruits or asparagus and weed sensitive vegetables like onions or garlic, will go a long way in producing a successful crop. This may take several years of cover cropping, tilling, solarization, or mulching before the main crop is planted.
- Step 11. Keep notes and records. What practices seem to work well; what rotations are suppressing weeds? What weeds are problematic? Change your practices – try different equipment, shallow cultivation vs inverting the soil, different cover crops, crop rotations, etc. Step 12. Stay educated by reading, attending workshops, conferences, field days, and talking with other growers. Come up with your own experiments (on a small scale) and compare it with your regular practices. Some examples of experimental practices: night time cultivation – eliminates the light stimulus for weed seeds that are brought to the surface. Reduces weed germination by 20-70%. Soil Solarization – covering the soil with clear plastic for several weeks/months during the hottest part of the summer to “cook” the weed seeds and rhizomes. Can be very effective on a small scale.
- There are many other good resources available – these are just a few.