Mould on tomato

Pathogen

The fungus Botrytis cinerea.

Host range

More than 200 plant genera, primarily broad leafed plants.

Identification

Signs and symptoms

Gray mold infection on a tomato leaf

• Leaves have irregular to V-shaped brown blotches, often starting at the margin of the leaf.
• Die-back symptoms appear as infection progresses from leaves, through petioles, towards the main stem.
• Brown, oval lesions can girdle the stem. 

  

  Gray mold infection on tomato stems

• Infected fruit develop a pale, soft, watery rot.
• Fruit symptoms occur on green and red fruit; while on the plant and post-harvest.
• Failed fruit infection results in white rings or halos on the fruit, called ghost spots. 

  

  Small white rings on tomato fruit indicate failed gray mold infections

• Infected flowers turn brown and die.
• In high humidity, fluffy gray spores cover infected plant parts.
  • The spores are light brown-gray on black stalks.

Environment

• Cool temperatures of 60-75°F (60-70°F optimum)
• Temperatures greater than 82°F suppress fungal growth and sporulation.
• High humidity (greater than 80%)
• Spore germination is optimal with leaf wetness of 5 to 8 hours.

Biology and disease cycle

• The fungus survives on numerous weed hosts, as a saprophyte on dead plant material, and as hard resting structures (sclerotia) in plant debris and soil.
• Spores are spread short and long distances by wind and rain, equipment and workers.
• Infections begin on weak, dying or wounded plant tissue.