Gray mold of tomatoes

Pathogen

The fungus Botrytis cinerea.

Host range

More than 200 plant genera, primarily broad leafed plants.

Identification

Signs and symptoms

• 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

  

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

  

• 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 temperature 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

Resistant varieties

There are no tomato varieties with resistance to gray mold.

Cultural control

• Keep humidity and leaf wetness low by rolling up high tunnel sides, increasing ventilation, and avoiding overhead irrigation
• Space plants well to avoid excess humidity in dense plant canopies
• Remove infected stems, leaves and fruit in a plastic bag
• Clean up leaf debris on the ground
• Prune plants in the afternoon when the morning dew has dried
• Maintain consistent and adequate soil moisture to promote healthy plants and fruit
• Remove all plant debris at the end of the season

Chemical control

Fungicides are available for control of gray mold on tomato; however, they should only be used once cultural practices have been implemented. Fungicide-resistant gray mold has been reported on many crops. Apply fungicide according to label instructions. Rotate fungicide groups and/or tank mix fungicides to avoid producing fungicide-resistant isolates.

For a current list of fungicides for gray mold management see the Midwest Vegetable Production Guide.