Gray mold may appear at any stage of fruit development. Lesions are usually seen first near the stem end or on the side of the fruit touching other decayed fruit, soil, or standing water. Affected areas turn pale or light brown at first and may spread over part or all of the fruit surface. Diseased tissue is covered with a velvety gray growth when the fungus begins to produce spores. Berries may become cottony white. Affected flower parts turn brown.
Identification
Tissue infected with the gray mold fungus, Botrytis, is covered with a velvety gray growth when the fungus begins to produce spores. If the humidity is high, berries become cottony white with fungus mycelium. Decayed fruit remain fairly firm and contents do not leak. The velvety appearance of decayed tissue and the absence of liquid leaking from the fruit distinguish gray mold from other fruit rots such as Rhizopus.
Life cycle
The fungus that causes gray mold and blossom blight, Botrytis cinerea, is widespread, infecting dead or dying plant parts and causing decay on many crops. In the absence of hosts, the fungus can survive as small black resting structures called sclerotia or in infected plant debris.
When it is humid and cool, spores are produced on moldy fruit, other hosts, plant debris, or sclerotia. They are spread by wind and splashing water. During flowering, germinating spores may infect flowers, causing blossom blight or invading developing fruit. Young fruit may decay soon after infection or the fungus may remain dormant until later. Spores produced continue to infect other fruit throughout the season. The incidence of fruit infection increases with the length of time fruit remains wet.
Gray mold is favored by cool, damp conditions, especially rainy weather. Botrytis is most active at temperatures of about 65 to 75°F.
Solutions
Fruit decay can be kept to a minimum by using raised beds, plastic mulch to keep fruit from touching the soil, and drip or furrow irrigation to keep water off the foliage and fruit. Make sure the plants are spaced far enough apart so that there is good air circulation around the fruit. Using stepped planter boxes that allow fruit to hang down over the sides may help improve circulation. Remove moldy fruit to reduce disease inoculum. If sprinklers are used, water in the morning so that plants will dry off during the day.
