Organic Weed Management

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Presentation by Jim Shrefler for the July 2013 Horticulture Workshop for the Oklahoma Beginning Farmer and Rancher Program. Held at the Kerr Center for Sustainable Agriculture in Poteau, OK.

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Organic Weed Management

  1. 1. Organic Weed Management Jim Shrefler, Extension Horticulturist and Merritt Taylor, Professor of Agricultural Economics Oklahoma Cooperative Extension Service
  2. 2. Watermelon Trial - June 27
  3. 3. Watermelon Trial - July 10
  4. 4. Organics and Weed Management Is there a quick guide to organic weed control? Is it good to have weeds on your farm? Do organic growers just need to learn to accept weeds? Is learning to control weeds an ongoing process? Will there ever be an “organic” Roundup?
  5. 5. Organics and Weed Management Organic farming systems use vegetation management to: – Improve soil – Prevent soil loss and degradation – Enable production of field crops, forage and produce
  6. 6. Organics and Weed Management Organic farming systems use vegetation management to: – Improve soil – Prevent soil loss and degradation – Enable production of field crops, forage and produce
  7. 7. Organics and Weed Management Vegetation that is managed may include: – Intentionally planted annual and perennial cover crops – Annual and perennial cash crops Forages; Small Fruits – Naturally occurring plant species May include many species Some may be considered “weeds” Annuals and Perennials
  8. 8. Perennial Weeds May or may not have abundant seed production May survive the winter via roots or rhizomes May or may not be woody plants Include grasses, broadleaf and sedges
  9. 9. Annual Weeds Generally produce abundant seeds May be cool or warm season plants Are adapted to disturbed environments Have varied life cycle durations Seed may persist for years
  10. 10. Organic Weed Management Practices Various farm practices may contribute to weed management – Carefully timed planting of cover crops – Prevention of the introduction of undesirable plant species or cultivars – Carefully timed planting of cash crops – Prevention and removal of undesirable weeds in cash crops
  11. 11. Organic Vegetables in USA South Central Plains Weeds pose a big challenge to all growers With organics, normally manageable issues   major concerns – e.g. annual grasses
  12. 12. Weed Control Methods for Organic Vegetables Prevention Cultural / Management Soil preparation Exclusion Mechanical Pruning / mowing / flaming Chemical Allelopathy
  13. 13. Prevention Avoid Introducing new weeds – Organic mulches – Manures – Moving contaminated equipment – Irrigation water – Moving soil
  14. 14. Prevention Watch for new weeds that appear – Do not allow them to go to seed – Seed may persist for many years – If perennial, watch for regrowth from vegetative propagules
  15. 15. Cultural / Management
  16. 16. Allelopathy Organisms that release “chemicals” that inhibit growth of other organisms May be while the plant is alive or during its decomposition Certain varieties of cereal rye are an example
  17. 17. Application methods Crop safety Efficacy Preemergence Weed Control Corn Gluten Meal Onions Summer Squash 
  18. 18. Soil Preparation Use sound practices that do not harm soil Eliminating all “green” can be a good starting point
  19. 19. Exclusion Barriers that prevent weeds from establishing Plastic mulch Landscape fabrics Carpet scraps Organic mulches
  20. 20. Mechanical Cultivation, hoeing, hand removal Labor intensive Proper equipment makes a big difference!
  21. 21. Cultivation for Weed Control in Organic Vegetables For some crops, such as cucurbits, cultivation has limitations Vining growth habit Shallow roots Wet soil conditions may preclude effective cultivation
  22. 22. Pruning / mowing / flaming Anything the gets above ground parts of weeds – Grazing – Flaming – Mowing – String trimmers We will see some examples later
  23. 23. Chemical Synthetic chemicals are not allowed in organics – Glyphosate, 2,4-D, “Poast” Natural weed control “chemicals” are being developed – Vinegar – Plant extracts, oils – These are “burn down” products – A natural “Roundup” is not yet available
  24. 24. Postemergence Herbicides for Organics
  25. 25. Integrated Management
  26. 26. Opportunities Rye – a common winter cover crop Rye has been shown to suppress germination / establishment of weeds Various practices could be used to establish vegetables following a rye cover crop
  27. 27. Objectives Compare field preparation / planting system practices for: – Impact on squash productivity – Weed incidence and removal costs Compare treatments for production cost / economic benefit relationships
  28. 28. Materials and Methods 2004 Soil – Bernow fine sandy loam Field history – 2 year fallow – Abundant crabgrass and tumble pigweed Soil test and apply nutrients with poultry litter in autumn Beds – 6 foot centers Sow „Elbon‟ Rye
  29. 29. Materials and Methods 2005 Divide field  3 planting dates – May, June and July Mow cover crop, prepare plots and plant Transplant Zucchini squash „Revenue‟ – Spacings: Rows 1.8 m and plants 0.77 m Drip irrigation Weeds – count and hand hoe Harvest squash over about 3 weeks
  30. 30. Treatment Advance Procedures At Plant Procedures Conventional Mow, Rework Rototill Black plastic M+R; Plastic Nothing Stale seedbed M+R Burn Mow M M Mow & Burn M M+Burn Shallow till M Till (2-5 cm) St & Burn M Till+Burn Treatments
  31. 31. Response Variables Squash Yields: – Impact on squash productivity Number of marketable fruit Weed incidence – Annual weeds Weed removal requirements – Hoeing time
  32. 32. Squash Yields* First Planting Date 0 20 40 60 80 conven plastic stale seedbed mow mow & burn shallow shallow & burn Fruitperplot * Harvest period of 3 weeks LSD (0.05)=15.4
  33. 33. Squash Yields* Second Planting Date 0 40 80 120 160 conven plastic stale seedbed mow mow & burn shallow shallow & burn Fruitperplot * Harvest period of 3 weeks LSD (0.05)=23.6
  34. 34. Summary – Squash Yields Plastic mulch best with May planting Any tillage, especially at-planting tillage, was better than no tillage with June and July plantings – * conventional and shallow tillage were comparable
  35. 35. Crabgrass First Planting Date 0 400 800 1200 1600 2000 conven plastic stale seedbed mow mow & burn shallow shallow & burn 3 weeks 5 weeks Plants/m2
  36. 36. Crabgrass Second Planting Date 0 400 800 1200 conven plastic stale seedbed mow mow & burn shallow shallow & burn 2 weeks 4 weeks Plants/m2
  37. 37. Crabgrass Third Planting Date 0 100 200 300 400 conven plastic stale seedbed mow mow & burn shallow shallow & burn 1 week 5 weeks Plants/m2
  38. 38. Summary – Crabgrass Crabgrass response to treatments varied with planting dates For PD1 and PD2 – greatest early emergence with conventional and/or stale seedbed PD3 – appreciable emergence in all except plastic and non tilled plots
  39. 39. Conclusions The optimum system may depend on planting date – Plastic always produced greater or comparable yields – Weed patterns will probably differ across dates Shallow and conventional tillage yields were comparable – Are there benefits to shallow tillage?
  40. 40. Interesting results in 2005 Plastic mulch always best with early planting Weed control results varied with dry (2006) and wet (2007) conditions Predictability as a weed control tactic is questionable Results Over 3 Years
  41. 41. In Summary Learn your weeds Strive to prevent new weed infestations Learn and apply good management practices When all else fails – Keep on Hoeing!

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