Botrytis Bunch Rot

Botrytis bunch rot causes fruit clusters to decay and become moldy, particularly in grape vines grown in cool, damp regions of the Pacific Northwest. You see brown rot spreading through berry bunches in wet spring weather. California grapes are particularly susceptible. Manage by improving air circulation through pruning, avoiding overhead irrigation, and removing infected fruit promptly.

Reduce moisture around affected tissue by improving drainage and air circulation. Remove rotted material cleanly and dispose of it away from the planting area. Avoid wounding healthy tissue during cleanup, as fresh wounds create new entry points. If the problem keeps returning, evaluate whether the site is too wet or poorly drained for the species you are growing.