Berries - Botrytis Fruit Rot and Gray Mold

Many fungi are capable of rotting mature or near-mature fruits of strawberry, grape, raspberry, blueberry and blackberry. Serious losses can occur under favorable environmental conditions for disease development. One of the most serious and common fruit rot diseases is gray mold. The gray mold fungus can affect petals, flower stalks (pedicels), fruit caps and fruit. In wet, warm seasons, there is probably no other disease capable of causing a greater loss of flowers and fruit. The disease is most severe during years with prolonged rainy and cloudy periods during bloom or during harvest. Although berries of all grape varieties are susceptible to bunch rot, losses generally are greater on tight-clustered varieties of Vitis vinifera and French hybrids.

Symptoms:

Young blossoms are usually very susceptible to infection. One or several blossoms in a cluster may show blasting (browning and drying) that may extend down the pedicel. Fruit infections usually appear as soft, light brown areas on the fruit which enlarge rapidly. Infected fruits remaining on the plant usually dry up, "mummify," and become covered with gray, dusty spores, which give the disease its name "gray mold." Fruit infection is most severe in well-protected areas of the plant, where the humidity is high and air movement is poor. On strawberry, berries resting on soil or touching another decayed berry or a dead leaf in dense foliage are most commonly affected. The disease may develop on young green fruits, but fruits become more susceptible as they mature. The disease is not usually detected until fruits are mature at harvest time. After picking, mature fruits are extremely susceptible to gray mold, especially if bruised. The handling of infected fruit while picking will spread the fungus to healthy ones. Under favorable conditions for disease development, healthy berries may become a rotted mass within 48 hours of picking.