potato data slides 1994

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Breaking the Late Blight Cycle In a Seed
Production Environment
W. R. Stevenson University of Wisconsin -
Madison, Department of Plant Pathology
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Potato Late Blight
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Potato Late Blight
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Potato Late Blight
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Potato Late Blight
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Potato Late Blight
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Why Do We Worry About Late Blight In A Seed Area ?

• Seed potatoes are generally grown in cooler
  climates more favorable for late blight
  development
• Late blight pathogen is wind borne, long
  distances
• Late blight pathogen is tuber-borne
• Late blight is a community disease

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Why Do We Worry About Late Blight In A Seed Area ?

• Concerned customer base
• Possible loss of crop certification
• Cost of disease control
• 50 per acre ? 250 per acre
• "Triple bottom line"
• financial viability
• environmental responsibility
• responsibility to society

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The Late Blight Cycle

• Pathogen arrives in seed area via wind or seed
• Infection of susceptible, unprotected plants
• Before adequate fungicide programs
• Poor or no fungicide coverage
• Long wet and cool period
• Disease spreads rapidly
• Control costs escalate
• Tuber infection
• Pathogen survives winter on tubers
• Repeat the cycle

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Breaking The Cycle

• Tougher seed standards
• Currently allow 1 seed infection
• Some states force growers to plant only certified
  seed
• Rejection of seed lots when late blight on
  foliage
• Would a field be rejected for 1? 10? 100?
  1000? lesions per field??
• Can we predict tuber infection on basis of
  foliage infection??

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Potato Late BlightA Little Inoculum Goes a Long
Way

• 1 seedpiece infection
• 10 ft-diameter area killed from 1 infected
  seedpiece

10 foot diameter
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Potato Late BlightA Little Inoculum Goes a Long
Way

• 1 seedpiece infection
• 10 ft-diameter area killed from 1 infected
  seedpiece
• 25 of the area of the field

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Breaking The Cycle

• Tougher seed standards
• Currently allow 1 seed infection
• Some states force growers to plant only certified
  seed
• Rejection of seed lots when late blight on
  foliage
• Would a field be rejected for 1? 10? 100?
  1000? lesions per field??
• Can we predict tuber infection on basis of
  foliage infection??

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Breaking The Cycle

• Rules regarding cull piles
• WI mandatory cull pile destruction by May 20
• Bury
• Grind and spread
• Landfill
• Feed to livestock

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Breaking The Cycle

• Volunteer potatoes
• Mild winters or heavy early fall snows
• Early season planting of row crops peas, beans,
  corn
• Lack of effective herbicides
• Are volunteers a public nuisance?

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Breaking The Cycle

• Seed purchase and handling
• Know the seed grower
• Visit the grower, walk the fields, view the
  storages
• Ask for field records
• IPM scouts
• Certification inspectors
• Shipping point inspection

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Breaking The Cycle

• If late blight risk associated with seed -
• Consider treating seed with Tops/MZ/Curzate
  Evolve
• Consider treating field with protectant fungicide
  at emergence
• If late blight pathogen confirmed on seed -
• Consider the consequences of planting infected
  seed
• Increased management costs
• Risk to crop in field and storage
• Community source of late blight

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Breaking The Cycle

• At emergence (risk of late blight in seed,
  volunteers or cull pile)
• Consider treatment with protectant fungicide
• At row close or at 18 severity values
• If no late blight, but risk high (18 severity
  values)
• Protectant spray with chlorothalonil, mancozeb,
  metiram
• Repeat at 5-7 day interval depending on crop
  growth and weather

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Breaking The Cycle

• If late blight present in area, but not in field
• Treat with cymoxanil plus chlorothalonil,
  mancozeb, metiram immediately
• Continue at tight interval for three sprays then
  protectant alone

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Breaking The Cycle

• If late blight present in field in pockets
• Disk hot spots with perimeter
• Treat rest of field and adjacent fields with
  cymoxanil immediately, and again in 5 days
• Then continue with protectant program

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Breaking The Cycle

• Late blight throughout field
• Destroy field immediately and treat adjacent
  fields with famoxate/cymoxanil immediately and
  again in 5 days
• Continue with protectant program

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Breaking The Cycle

• Mid Season
• Focus on protectant program that may include
  Curzate, Acrobat or Tattoo
• Scout fields weekly or even more often
• Careful irrigation to avoid excess

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Breaking The Cycle

• Late Season
• Focus on protectant program that may include
  Acrobat, Tattoo
• Apply vine desiccant to protect size of seed
  potatoes and to allow at least 3 weeks of dead
  vines before harvest
• Careful irrigation to avoid excess

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Summary

• Effective late blight strategy focuses on
• Keeping the fungal pathogen out of the planting
  area
• Intensive monitoring of every field
• Careful monitoring of weather conditions
• Careful application of fungicide
• Partnership between each and every grower
• Prompt response to local outbreaks

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