Diseases of tomato (
Botrytis (gray mold)
Gray mold is caused by the fungus Botrytis cinerea. The fungus has a wide host range and attacks its hosts in warm, moist conditions. Therefore, it is rarely a pathogen outside the greenhouse in Arizona. It is an efficient saprophyte, enabling it to survive in debris for long periods of time. Wounds are the most probable entry sites. In Arizona greenhouses, it is most common on lower stems that have been pruned. Early symptoms are water soaked lesions that become light tan if the infection does not progress (photo 1). Under high humidity, and particularly during cloudy weather, the fungus will produce spores that are easily disseminated in air currents, by workers, and by infested cuttings that are moved through the greenhouse (photo 2). Spore production gives the infection a fluffy gray appearance (photo 3). Active lesions girdle the stem and plants wilt (photo 4).
Controlling the humidity and applying fungicide to pruning wounds is the best way to prevent gray mold. Relative humidity below 80% reduces disease development. Reduction of the canopy is also helpful, and infected plant parts should be removed immediately. Infested material should be removed from the greenhouse carefully to avoid spreading fungal spores and the debris disposed of off site or as far from the greenhouse as possible. Fungicide resistance is common, and rotation or combinations of fungicides are very important.
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February 24, 2003