Weed Management in Vegetables

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Weed Management in Vegetables

• David Monks
• Dept. of Horticultural Science

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Weeds cause

• Reduce yields - yields can go to 0.
• Reduce quality - nutsedge growing in tubers
• Contaminants - cocklebur in greens
• Cover for rodents
• Interfers with harvest
• Hosts for diseases (ie maize dwarf mosaic virus)
• Hosts for insects

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Broadleaf Weeds

• Pigweed- Palmer amaranth, smooth pigweed
• Common lambsquarters
• Morningglory
• Cocklebur
• Smartweed
• C. Ragweed

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Grass Weeds

• Common crabgrass
• Goosegrass
• Broadleaf signalgrass
• Fall panicum
• Barnyardgrass
• Annual bluegrass

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Weeds

• Summer crops
• summer annual weeds North Carolina
• winter annual weeds Mountains and Piedmont North
  Carolina
• Winter crops
• winter annual weeds North Carolina
• summer annual weeds Eastern North Carolina

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Weed Management in Vegetables

• Cultural practices
• Crop competition, weed-free transplants, plastic,
  rotation
• Cultivation
• Herbicides

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Weed Management Strategies

• Kill all weeds prior to planting
• non selective chemical
• tillage
• Apply available broadleaf and grass herbicides
• Monitor each field for weeds to detect changes in
  weed spectrums ie sicklepod

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Weed Management Strategies

• Implement remedial control measures
• cultivation
• herbicide
• Prevent seed production

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Cultural Practices

• Healthy vigorous crop - suppresses weeds
• Irrigation
• Full stands
• Proper fertilizer
• Crop competition - vegetables are weak
  competitors
• peppers- 12 cocklebur/40 ft reduced yield 67
• tomato- 4 redroot/ 40 ft reduced yield 30
• squash critical weed free period- 3 to 4 weeks

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Cultural Practices

• Growth habit of vegetable crops affect
  competition
• vine crops- cucurbits, sweetpotatoes, pumpkin
  provide shade later in season
• upright crops solanaceous crops (tomato,
  eggplant), pod crops (okra)- do not shade soil
  and weeds quickly

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Growth Habit contd

• Pickling cucumbers require 12 to 36 days of
  weed-free maintenance to prevent yield reductions
• Transplanted tomatoes and pepper require 4 to 5
  weeks of weed-free maintenance

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Cultivars and Competition

• Potatoes (NY)- Katahdin is less competitive than
  Norchip
• Tomatoes (NY)- Supersonic gave almost complete
  pigweed control compared to New Yorker

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Cultural Practices

• Rows vs broadcast
• broadcast
• short seasoned leafy crops
• weeds greatly impact these crops
• rows
• longer season
• crops have time to recover from weed competition

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Postemergence Weed control

• Herbicides
• Tillage
• average of 2 to 3 cultivations
• 1 to 2 hand weedings

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Scout for Weeds

• At least 1 to 2 times per week
• Palmer amaranth grows 1 to 2.5 inches per day
• Scout in a random fashion to detect weeds
• weeds grow in patches
• Scout noncrop land for new weeds
• sicklepod

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Tillage

• Preplant tillage- deep vs shallow tillage vs no
  tillage
• Shallow tillage after planting prior to crop
  emergence
• Precision cultivation soon after crop emergence

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Cultivation Timing

• Cultivation after crop was established
• dependant on weed and crop size
• cultivate when weed are small ie prior to tiller
  initiation of tillers (grasses)
• shallow
• less than 2 inches deep
• deeper results in crop root damage and movement
  of weed seeds to near soil surface
• weather can affect implementation

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Hand Removal

• Hand remove when less than 2 inches tall
• weeds larger than 2 inches have extensive root
  development
• weeds can be hoed, pulled or clipped depending on
  their stage of development

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Herbicides

• Preplant herbicide
• glyphosate or paraquat- less than 10 of acreage
  receive a preplant herbicide
• Preemergence herbicide
• approximately 60 of acreage of most vegetables
  receive a preemergence herbicide
• must be activated within a few days of
  application
• grass broadleaf herbicide

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Herbicides contd

• Postemergence herbicide
• less than 25 of acreage receives a postemergence
  herbicide
• at least 60 to 80 of soybean acreage receives a
  postemergence herbicide
• herbicide resistant vegetable crops
• lettuce
• potatoes
• sweet corn

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Herbicide contd

• Postemergence herbicides must be timely
• weeds must be small
• weeds must be actively growing
• very safe to crop

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Prevent Weed Seed Production

• Prevent weeds from producing seeds
• weeds are heavy seed producers
• seeds last for many years

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Weed Seed

• Duval buried 107 weed species 8, 22 and 42 inches
  deep.
• 1 year 71 species germinated
• 6 years 68 species germinated
• 10 years 68 species germinated
• 20 years 57 species germinated
• 30 years 36 species germinated

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Weed Seed

• Barnyardgrass 7,160 seeds/plant
• Curly dock 29,500
• C. lambsquarters 72,450
• R. pigweed 117,400
• C. Purslane 52,300
• C. ragweed 2,380
• P. Smartweed 3,140