Botrytis Grey Mold

A.K.A. Grey/Gray Mould, Botrytis blight, Botrytis Grey mould, etc.

Causal Organism: Botrytis cinerea

Crops Affected:
Very wide host range – asparagus, lettuce, onion, garlic, leeks, cucurbits (pumpkin, squash, cucumber, melons), beans, potato, tomato, eggplant, pepper, strawberry, raspberry, etc.

Disease Cycle:

• Similar disease cycle for most crops, however disease symptoms and damage will vary with crop
• Widespread fungal pathogen of dead or dying plant material (saprophyte)
  • Sensitive, weak or damaged tissues (young/tender, stressed, mechanically injured, etc.) or senescing tissues are typically most susceptible to infection
  • Green fruit may be affected in certain conditions
• Favoured by cool, humid conditions
• Initial infection typically comes from air-borne asexual spores (conidia) landing on susceptible tissues in the presence of water
  • Once infection occurs, sporulation occurs rapidly, with a rapid acceleration of growth
  • Spread is more rapid in dead or dying tissues (e.g. senescing or damaged tissues)
  • The pathogen produces large numbers of these conidia, particularly under cool and moist conditions
• Fungus spreads by breaking down tissues ahead of spread, producing a watery soft rot
• May spread between plants/produce by mycelium (in storage, etc.)
• Sclerotia (hardened clumps of fungal vegetative tissues) may form once tissues are fully colonized
  • Sclerotia may persist in dry soil and become an inoculum source
• Main spread is by conidia

Symptoms:

• May attack wide range of different plant parts, with the disease symptoms related to the death of those tissues
• May attack leaves, stems, floral parts, whole heads, bulbs, fruit, roots, etc.
• Name of the disease is often descriptive of the symptoms and plant parts attacked (e.g. onion neck rot; grey mould)
• Grey coloured mycelium and grey/brown spore-producing bodies are distinctive
  • Spores are produced in vast quantities
    • Water-soaked areas proceed the grey mouldy areas
  • Sclerotia are hard and black (may not form as readily as Sclerotinia)
    • Differentiated from White Mould (Sclerotinia) by the colour of mycelium
  • Fruit rots / Ghost spots
  • Infection typically occurs at the flower end – dead or senescing flowers/petals stick to the fruit
    • Fruit may abort
    • Infected fruit is usually attacked by secondary organisms, resulting in rots (wet or dry)
  • Bean pods may develop dark green, water-soaked lesions, which turn light brown to grey, with concentric areas
    • Small, black flattened mycelium may develop in pods
  • Tomato or pepper fruit may develop a tiny, brown necrotic spot surrounded by a pale halo of tissue
    • Often referred to as “ghost spot”
      • Typically occurs on green fruit, but may also occur on ripe fruit
      • Ghost spots often do not develop beyond the initial symptom but may reduce quality
    • Fruit infected at later stages (e.g. through petals stuck to fruit surface) may develop an irregular, brown lesion where the tissues make contact
    • Fruit may become infected at the stem end, by the calyx, with a water-soaked, soft rot developing
      • Fruit often drops
    • Fruit rots generally commence as a water-soaked lesion, that is slowly colonized and masses of grey spores developing
    • General post-harvest disease development (called “nesting”) develops as a dirty, white mycelium

Management:

• Ensure sites are well-drained
• Ensure good air drainage and avoid high humidity situations
• Ensure adequate but not excessive nitrogen applications (excess will result in lush, soft growth)
• Control weeds
• Clean up trash piles and bury crop residues and debris, which serve as a source of inoculum
• Control weeds to ensure good ventilation and air circulation
• Ensure all fruit and produce are harvested in a timely manner – over ripe fruit is more susceptible
  • Handle harvested produce correctly, removing field heat rapidly and holding at appropriate temperatures
• Irrigate at a time when plants will dry quickly
• Chemical controls are available for protection of the various crops. Timely application is critical for maximum success. See labels for application timing and rates. Adhere to appropriate Pre-Harvest Intervals.