Botrytis fruit rot (Gray mold) on caneberries—Botrytis cinerea
Flattened black masses of sclerotia appear on the canes
of Botrytis-infested caneberry plants in late winter. In
spring, sclerotia germinate to form masses of spores. Opened
flowers may become infected, and the fungus will sporulate
on the blighted flowers. Infected berries left on the vine
become mummified. In storage, white mycelia can cover infected
Botrytis fruit rot occurs under cool, wet conditions. Physical damage to the plant increases disease incidence, especially during the rainy season. The pathogen overwinters as sclerotia on infected canes and sometimes as mycelium in infected tissues. Spores from overwintering structures and dead leaves and mummified berries are the main sources of primary inoculum. Spores are dispersed by wind, rain, and overhead irrigation. Flowers are not susceptible to infection until they have opened. Infections generally remain dormant until fruit is nearly ripe, or after harvest. Infections can reoccur throughout the season by sporulation of the fungus on unpicked, overripe fruit left on the vine.
To promote air circulation and quicken drying of plant tissue, allow berries to ripen in an open canopy. Open canopies can be created by heavy pruning to maintain a narrow row of plantings, removing the first flush of primocanes, minimizing nitrogen fertilizer application, and controlling weeds. Training systems also help. Some red raspberry cultivars are partially resistant. Pick fruit during cool temperatures and refrigerate promptly. Remove fruit mummies and dead leaves before tying up fruit canes in the fall.
Botrytis sclerotia on canes
Botrytis spores covering fruit