Walt Stevenson

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Disease Problems and Solutions for Cole Crop
Growers
Walt Stevenson UW - Department of Plant
Pathology
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Cole Crop Diseases

• Black Rot - Xanthomonas campestris pv. campestris
• Black Leg - Phoma lingam
• Wirestem and Head Rot - Rhizoctonia solani
• Yellows - Fusarium oxysporum f. sp. conglutinans
• Club Root - Plasmodiophora brassicae
• Downy mildew - Peronospora parasitica
• Phytophthora Rot - Phytophthora porri

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Black Rot
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Black Rot
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Black Rot
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Black Rot
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Black RotKey Points

• Pathogen Xanthomonas campestris pv. campestris
• Plant can be affected at any stage
• Pathogen survives over winter in debris from
  diseased plants
• Pathogen is carried on and in seed
• Bacteria are spread by splashing or running water
• Spread long distances on seed and transplants

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Black RotControl Strategies

• Plant only pathogen-free seed or transplants
• Hot water seed treatment is effective
• Rotation (at least 2 years free of cole crops and
  crucifer weeds)
• Quick plow down of crop debris after harvest
• Avoid working in fields when foliage is wet
• Several cabbage varieties have black rot
  resistance
• Fixed copper sprays may delay spread in field

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Black Leg
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Black Leg
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Black Leg
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Black LegKey Points

• Pathogen Phoma lingam
• Can be serious problem in seedbed
• Fungus is carried on and in seed
• Fungus can survive at least 3 years in crop
  debris
• Spores are splashed from plant to plant

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Black LegControl Strategies

• Plant only pathogen-free seed or transplants
• Fungicide or hot water treatment of seed to
  eliminate fungus
• Rotation (at least 4 years free of cole crops and
  crucifer weeds)

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Clubroot
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Clubroot
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Clubroot
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ClubrootKey Points

• Pathogen Plasmodiophora brassicae
• Distinctive symptoms on roots
• Pathogen survives in soil for 10 years or longer
• Cool, wet, acidic soils favor this disease
• Spread on transplants and contaminated soil on
  equipment

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ClubrootControl Strategies

• Rotate seedbed and field plantings (10 years)
• Choose fields carefully to avoid surface water
  flooding
• Adjust soil pH to 7.2 (may not be compatible with
  other vegetable crops)
• Use of PCNB in transplant water
• Plant only disease-free transplants

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Yellows
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Yellows
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YellowsKey Points

• Pathogen Fusarium oxysporum f. sp. conglutinans
• Soil borne fungus
• Survives in soil for several years
• Plants infected through young rootlets
• Many members of cabbage family susceptible

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YellowsControl Strategies

• Rotation (at least 2-3 years)
• Plant yellows resistant varieties

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Downy Mildew
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Downy MildewKey Points

• Pathogen Peronospora parasitica
• Pathogen overwinters in diseased plant debris
• Disease is favored by cool, wet weather

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Downy MildewControl Strategies

• Plant disease free transplants
• Control in the seedbed is important
• Use of fungicide sprays

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Head Rot
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Wirestem and Head RotKey Points

• Pathogen Rhizoctonia solani
• Pathogen attacks plants in the seedbed, field and
  storage
• Pathogen is soil borne - indefinite survival

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Wirestem and Head RotControl Strategies

• Rotate seedbed and field plantings
• Consider fumigation of seedbeds
• Use of PCNB in seedbed and in transplant water is
  helpful

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Phytophthora Rot
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Phytophthora RotKey Points

• Pathogen Phytophthora porri
• Fungus survives in soil and crop debris
• Favored by wet, cool conditions
• May cause serious losses in storage

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Phytophthora RotControl Strategies

• Promptly destroy infected crop debris
• Rotation with crops other than crucifers, onions,
  leek
• Application of metalaxyl fungicide to the soil
  before planting

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Disease Control - Cabbage and Other
CrucifersAlternaria Leaf Blight, Downy Mildew

• Active Ingredient Product Comments
• maneb Maneb 80, Maneb 7 day PHI
• Zinc F4, Manex F4 Limit on total amount
• of product/A/season
• chlorothalonil Bravo 720, 90DG NO rotational
  restrictions
• metalaxyl/ Ridomil/Bravo Rotational
  chlorothalonil restrictions
• cupric hydroxide Kocide, Low efficacy with
  Champion high disease pressure