Botrytis gray mold is caused by the ubiquitous asexual fungus Botrytis cinerea (B. cinerea).

Botrytis affects many vegetable crops including tomato, pepper, bean, potato, onion, crucifers, and cucurbits as well as fruits, berries, and ornamentals.

Botrytis can affect all aboveground plant parts of tomato in both the greenhouse and field. This fungus occurs as both a pathogen and a saprophyte causing diseases such as damping off, stem girdling, foliar blighting, and postharvest rots.

Botrytis produces a dense velvety gray brown spore mass on infected tissue which when disturbed releases a cloud of spores (Figure 1). Tomato leaf and stem lesions are tan to brown in color. Stem infections occur during periods of high humidity through leaf scars, cracks, and pruning wounds. Spores can remain dormant for up to 12 weeks within pruning leaf scars and are triggered to germinate during plant stress. Stem lesions may expand in concentric rings to girdle the entire stem causing wilting above the infection site. Flower petals are very susceptible and can initiate infection of pedicels and developing fruit. Fruit lesions are typically a whitish soft rot and often the skin ruptures near the center of the decayed area allowing spores to form on exposed tissue (Figure 2). Small 3-8 mm whitish rings on the fruit surface are aborted botrytis infections known as ghost spots which reduce market quality.

Figure 1. Botrytis infection on tomato stem, showing brownish-gray, dry lesion and girdling of the stem. Masses of gray colour Botrytis spores can be seen on the surface.

Shawn Butler, NCSU PDIC

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Figure 1. Botrytis infection on tomato stem, showing brownish-gray, dry lesion and girdling of the stem. Masses of gray colour Botrytis spores can be seen on the surface.

Shawn Butler, NCSU PDIC

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Figure 2. Botrytis infection on tomato fruit, showing rotted tissue and spores.

Shawn Butler, NCSU PDIC

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Figure 2. Botrytis infection on tomato fruit, showing rotted tissue and spores.

Shawn Butler, NCSU PDIC

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• High humidity and moisture (4-6 hours of free water from dew, rain, overhead irrigation or greenhouse condensation is sufficient for infection).
• Cool to moderate temperatures (optimum growth 65-73°F).
• In North Carolina Botrytis typically occurs after midseason in the field and during postharvest shipping. The disease can occur year round in greenhouse production.

Pathogen spores are transported via wind, rain and greenhouse air currents. The fungus survives/overwinters as mycelia or sclerotia in plant debris and organic soil matter. Various other crops nearby may serve as pathogen sources. Fallen flowers are a common source of leaf infections.

• Currently there are no known B. cinerea resistant tomato cultivars
• Apply fungicides preventatively prior to dense canopy growth, rotate fungicides to manage resistance
• Avoid overhead irrigation, minimize plant wetness
• Do not work on wet plants, prune plants in the early afternoon allowing wounds to dry quickly
• Ventilate greenhouses to maintain relative humidity at less than 90%
• Temperatures above 70°F discourage Botrytis development
• Practice good greenhouse sanitation, scout, bag, and remove infected plants

Botrytis gray mold of tomato can be controlled by using cultural practices, however, if disease pressure is high, fungicide sprays may be helpful to control disease. For the latest fungicide recommendations for gray mold see the Southeastern US Vegetable Crop Handbook. Fungicide labels are legal documents, always read and follow fungicide labels.

Gray mold can be successfully controlled using cultural practices as listed above.

Gray mold can be successfully controlled using cultural practices as listed above.

• The NC State University Plant Disease and Insect Clinic provides diagnostics and control recommendations
• The Extension Plant Pathology Portal provides information on crop disease management
• The Southeastern US Vegetable Crop Handbook provides information on vegetable disease management
• The USDA Fungus-Host Distributions Database provides information about reported hosts for fungal and oomycete pathogens

This factsheet was prepared by the NC State University Vegetable Pathology Lab in 2015.

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