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Gray mold of tomatoes

Quick facts

  • Gray mold thrives in the high humidity found in high tunnel tomato production.
  • Gray mold is rare in Minnesota field grown tomatoes. 
  • The fungal pathogen infects all above ground plant parts. 
  • It can be highly destructive when environmental conditions favor disease.

Pathogen

The fungus Botrytis cinerea.

Host range

More than 200 plant genera, primarily broad leafed plants.

Identification

Signs and symptoms

Tomato leaf with irregular to V-shaped brown blotches, starting at the margin of the leaf
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.
    Tomato stem end that grey, brown with dead leaves towards the end.
    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.
    Healthy green tomatoes with white rings or halos on the fruit
    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.

Management

 | 

Angela Orshinsky, Extension plant pathologist and Michelle Grabowski, Extension educator

Reviewed in 2016

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