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Hammermeister weed management


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  • 1. Weed Management under Organic Production Andrew Hammermeister Organic Agriculture Centre of Canada Dalhousie University, Faculty of Agriculture
  • 2. Ecology – The Science of Connections • “In living nature, nothing is unconnected from the whole”
  • 3. What is a weed? • Liebman et al. (2001) define agricultural weeds as “plants that are especially successful at colonizing disturbed, but potentially productive sites, and at maintaining their abundance under conditions of repeated disturbance.” • Schonbeck (2013): any plant not intentionally sown or propagated by the grower that requires management to prevent it from interfering with crop or livestock production.
  • 4. •
  • 5. •
  • 6. Plant community succession Disturbance • A disturbance creates a vacuum, unused nutrients, light, water • Natural ecosystems undergo ‘succession’ after disturbance. Empty space is quickly filled Annuals  herbaceous perennials  shrubs  forest • Cultivated agricultural systems artificially maintain the ecosystem at an immature state.
  • 7. Ecological function of weeds • Protect the soil from erosion • Replenish organic matter, feed and restore soil life • Absorb, conserve, and recycle soluble nutrients that would otherwise leach away • Absorb carbon dioxide from the • Restore biodiversity • Provide habitat for insects and animals
  • 8. Weeds have a variety of adaptations to disturbance (Mohler, 2001a): • Take up and utilize large amounts of soluble nutrients • High tolerance to stresses, excess nutrients, drought, waterlogging; temperature extremes; or repeated grazing, mowing, or tillage. • Rapid growth and formation of mature seeds, vegetative propagules, or both • Rapid seed germination in response to light, nutrients, scarification (scratched seed coat), etc.
  • 9. Weeds are adapted to disturbance (Mohler, 2001a):(Mohler, 2001a): • Prolific seed production (up to hundreds of thousands per plant) • Seed characteristics that promote wide dispersal: small size, pass through digestive tracts, burrs attach to fur, and easy wind dispersal • Seed dormancy mechanisms and seed longevity in the soil that allow seeds to “wait” for favorable growth conditions before germinating • Ability to regrow or reproduce from small fragments of root, rhizome (underground stem), tuber, or other underground structures (Mohler, C. L. 2001a. Weed life history: Identifying vulnerabilities. p. 40–98. In M. Liebman et al. Ecological management of agricultural weeds. Cambridge University Press, New York.)
  • 10. Weed seeds • Some weeds produce dozens of seeds per plant, others may produce 10s of thousands • Weed seeds can survive in the soil for less than 1 year to several decades depending on the species • Some weeds germinate immediately, others may require several years of burial before germinating Seed Longevity of 41 Weed Species Buried 17 Years in Eastern and Western Nebraska. Burnside et al. 1996. Weed Science , Vol. 44, No.1, pp. 74-86
  • 11. Diagram of the maximum emergence depth of a range of weed species according to seed weight (size). (Based on Roberts, H. A. (Ed.). (1982). Weed Control Handbook (7th ed.). Oxford: Blackwell Scientific Publications.)
  • 12. Weed problems occur when a sufficient weed seed population encounters a favorable environment for weed growth in the presence of a crop that is susceptible to the effects of weed competition. Figure credit: Ed Zaborski, University of Illinois (adapted from Schonbeck and McCann, 2007)
  • 13. Production costs of weeds • Competing directly for light, nutrients, moisture, and space • Releasing natural substances that inhibit crop growth (allelopathy) • Physically hindering crop growth and development, especially climbing vines like morning glories, Ipomoea spp.; and hedge bindweed, Calystegia sepium • Hosting pests or pathogens that may attack crops • Promoting disease by restricting air circulation around the crop • Interfering with or contaminating crop harvest • Reproducing prolifically, resulting in a greater weed problem in the future • Parasitizing crops directly (e.g., dodders, Cuscuta spp.; and witchweed, Striga asiatica)
  • 14. How do we make money and reduce pesticide use? • Creativity – Look at the problem from another angle – Why is the weed there? – Why is it more competitive than the crop? • Pesticide applications are a reaction to the problem – Weed outbreaks are not due to a herbicide deficiency!!!
  • 15. Integrated Weed Management • Herbicides • Roguing • Mechanical weeding • Flaming Chemical Cultural Rotations Seeding rate Crop selection Cultivar choice Delayed seeding Physical Biological • Few biopesticides for weeds
  • 16. Weed management options Weed Management Strategies •Enhance crop competitiveness •Remove or curtail weed growth in critical early crop development •Reduce weed seed bank in soil
  • 18. Prevention of Weeds • Diversify your cropping system • Control weeds in hedge rows, ditches, manure/compost piles • Use weed-free seed • Clean equipment to prevent spread • Work patches of rhizomatous weeds separately, and clean equipment • Clean equipment between fields • Compost manure properly (60oC for 3 d) • Catch chaff from combine
  • 19. Preparation • Prepare the planting site well – Get rid of perennial weeds before planting – Optimize fertility for the crop (incl. pH) – Consider summer fallow if coming out of grass – Have a good seed bed – Have proper drainage
  • 20. Improve crop competitiveness: seedbed preparation • • • • Level fields Reduce planting speeds to ensure uniform depth Plant into a firm seedbed and/or pack behind the seeder Good seed soil contact essential for rapid and even establishment • Packing before planting: – Stimulates a flush of weeds – Creates a firm seedbed – Creates uniform and firm soil for fingerweeding • Packing after planting: – Improves seed-soil contact – Can stimulate competitive weed growth (use a seeder that packs only in row)
  • 21. Improve Crop Competitiveness: Seed and Seeding • Seed – – – • Competitive cultivar Seed purity: damaged seed, weeds, other materials Viability, germination, vigour Rate – • Higher rates are more competitive Depth – – • Deeper planting delays emergence, can be used strategically, but not for small-seeded crops or less competitive crops Deeper seeding allows pre- and post-emergent tillage Timing – Crop and weed problem dependent – – • Early planting – competes with late emerging weeds Delayed planting allows control of early weeds, better vigour for some crops Spacing – Optimize competitiveness, want even seed distribution
  • 22. Soil Nitrogen Status and Seeding Rate High N, low seeding rate Low N, high seeding rate
  • 23. Features of Good Crop Rotations For Weed Management For weed suppression • • • • Crops that develop slowly or are less competitive should follow weed suppressing crops Alternate leaf crops with straw crops Alternate between spring sown and winter sown crops Select crops that are competitive with weed problem Row crops can be used to control some weed problems Intercropping to increase crop competitiveness, compensate for variability in soil
  • 24. Rotation Examples: Prairie Organic Farm (Ian Cushon) • Alfalfa x2: seed + bees – Seed 50-100 lbs/ac @ $2-3/lb – Bees $100/10,000 – Gross $250-$500/ac • Hemp – 500-1200 lbs/ac @$1/lb for oil • Lentil – 600 lbs/ac (10bu/ac) $0.6/lb • Flax (underseeded to alfalfa) – 10 bu/ac @$30/bu • Total: $1660-$2860/ac/5yrs – $332-$572/yr (3,500 acres)
  • 25. Rotation example: Quebec Dairy Farm - 30 cows – – – – – Forage Forage Forage Forage Forage • • • – – Break after 1st cut 2 months of weed (couch grass) control Apply manure & lime Spelt or corn for feed Mixed crop for feed underseeded to forage • Critical success factors: – Optimize soil pH, drainage, land levelling – Forages for weed control and soil building – Roguing weeds in corn – Would like to add soybean • Grows short season corn
  • 26. Canada thistle • Alfalfa for 3 years • Mow when in flower • Frequent shallow spot tillage • Till patch and clean off equipment
  • 27. Green Manure Crops • Pest Management – Smother weeds – Break pest cycles • Weed control: – – – – – – – Ryegrass buckwheat fall rye winter wheat oilradish mustard legumes (alfalfa, sweet clover, white clover once established)
  • 29. Critical weed free period
  • 30. Critical weed free period
  • 31. Critical weed free period
  • 32. Critical weed free period
  • 33. Earthworm: numbers & biomass Nelson and Lynch, 2008 Numbers Biomass c ab c 200 a a a ce yr s 2 1 yr sin at o a a b sin ce 3y rs sin 4/ ce 5 yr ss in ce Re fe re nc e 0 c bc b 100 a c a 0 a a c a b yr sin ce 2 yr ss in ce 3y rs sin 4/ ce 5 yr ss in ce Re fe re nc e b 200 at o 400 c Phase of the Rotation (years) 1 2006 data 2007 data c 2006 data 2007 data Po t c Biomass (fresh mass gm -2) 600 Po t Numbers (individuals m -2) 300
  • 34. • False seed bed: A seedbed is prepared, weed seeds in the top 5 cm / 2” of soil germinate and then emerge, the soil is then re-tilled (cultivated) with the minimum disturbance necessary to kill weed seedlings, the crop is then sown, germinates and emerges from mostly weed free soil.
  • 35. Stale seed bed: Final seedbed is prepared, weed seeds in the top 5 cm / 2” of soil germinate, crop is sown, weed seedlings emerge, immediately prior to crop emergence weed seedlings are killed by a thermal weeder, crop emerges from weed free soil.
  • 36. Stale seed-bed • Control weeds before the crop emerges or just prior to transplanting. • Burn down herbicides • Flame weeding? – Kills small weeds – Doesn’t disturb soil
  • 37. Hit weeds when small; light cultivation
  • 38. Finger/tine weeder
  • 39.
  • 40. Camera guided wide blade
  • 41. Wet conditions… major challenge
  • 42. Roguing
  • 43. Reigi Weeder – 6 acres a day, 2 people & small tractor – Best on small weeds –
  • 44. Till and mow Discourage rodent damage by removing weeds
  • 45. Mulching in apples
  • 46. Black Currant Weed Management Research • The Questions – What is the most cost effective means of controlling weeds in small bush fruits? – How do these treatments affect soil biology? • The Treatments • • • • • Mowing Cultivation Flaming Acetic Acid + tilling Mulches • Black plastic • Black woven cloth • White woven poly • Straw • Bark
  • 47. Weed management trial in Dalhousie orchard (Note: the crop in the following slides is black currants but the following discussion should apply to haskap also.)
  • 48. Cultivation - 6wks after planting
  • 49. Acetic Acid herbicide - 6wks after planting
  • 50. Mowed – 6 weeks after planting
  • 51. Plastic - 6wks after planting
  • 52. Plastic vs. mowed 14 months after planting
  • 53. Bush size (m3 plant-1) 0.7 a 0.6 ab 0.5 ab ab b b 0.4 b 0.3 0.2 0.1 c 0 Figure 1. Bush size at the end of 2012. Error bars show standard error of the mean. Bars with the same letter group are not significantly different (p<0.05).
  • 54. 400 Black Plastic Soil Degree Days 350 300 Black Fabric 250 200 Mowing Cultivation+A cid Hay+Plastic Cultivation White Fabric 150 Straw 100 50 0 0.140 0.150 0.160 0.170 0.180 0.190 0.200 0.210 Average Soil Moisture (m3/m3) Figure 2. Soil temperature (degree days) vs. average soil moisture from JuneSeptember 2012 as measured by soil probes buried 10 cm deep in each plot (n=32).
  • 55. 1.0 . Speci2 M. subterranea MediTanP. carbonarius B. rupestris D. filiformis SmalAtht Black plastic + hay Black plastic C. obscura T. corticinus S. notangulus L. intermedius D. globulosus Speci3 Small-bl MediBlac A. familiaris H. capillaricornus A. apicalis Straw -0.6 E. anceps Cultivatated soil -1.0 Slender1.0 Fig. 5. Relationship between extracted beetle taxa and plot types (cultivated soil, black plastic, black plastic + hay, or straw) as shown by a principal component analysis biplot.
  • 56. Cost Effectiveness (cm3/$) 450 400 350 300 250 200 150 100 50 0 a b c cd c cd cd d Figure 3. Cost effectiveness (bush volume per dollar spent) at the end of two years of growth. Columns with the same letter are not significantly different (p<0.05).
  • 57. Summary • Organic weed management requires an integrated approach – Prevention – Cultural control – Physical control – Chemical or flaming control • More approaches used at the same time dramatically increase success of weed management • Keep weeds in perspective
  • 58. Visit OACC.INFO for • Production, research and market information • Upcoming workshops & symposiums • Virtual farm tours • Organic award winners • Organic policy toolbox • Monthly e-zine