Protect Hail-Damaged Grape Clusters From Botrytis

Recent hailstorms hit Northwest Michigan hard. Grapes, tart cherries, and apples orchards were hit by high winds and nickel- to quarter-sized hail, says says Nikki Rothwell of Michigan State University Extension.


“Canes have been gouged and blown off the trellis, leaves are tattered and berries have been split open,” writes Annemiek Schilder of Michigan State University Extension. “Wounds on leaves and canes will probably not have any major further consequences unless crown gall bacteria present on the vines take advantage of the wounds to enter canes.”

Schilder suggests growers scout for crown gall bacteria. Injured fruit is more susceptible to rot and especially Botrytis cinerea, which causes Botrytis bunch rot.

“We don’t want to invite Botrytis to establish itself in the cluster as it may cause problems later during fruit ripening. Botrytis is somewhat of an opportunistic pathogen, invading weakened, damaged or senescent plant tissues,” she writes.

Botrytis can be found in humid conditions, is windborne, and may already exist in clusters as latent infections. Because of these conditions, Schilder suggests growers apply fungicides to damaged clusters.

“Systemic fungicides are recommended for better coverage and some ‘back action’ in damaged grapes,” Schilder writes.