White Drupelets on Raspberries and Blackberries
Compiled by Gail Ruhl, Senior Plant Disease Diagnostician, Purdue University
White drupelet syndrome is a tan to white discoloration of individual drupelets on blackberry or raspberry fruits. Several different explanations for this symptom have been proposed.
The Department of Horticulture at Cornell University notes that the most common cause of white drupelets on red raspberries is solar injury (sunscald) due to UV radiation and that varieties vary in susceptibility to this noninfectious disorder.
Several other explanations of causal factors for this condition on blackberries include, stinkbug damage, red berry mite feeding damage, sunscald and UV radiation. Damage attributed to stinkbug insect feeding on young fruit and feeding damage by red mites purportedly produces a random pattern of off color drupelets.
The diagnostic clinic in Arkansas (pdf file) reports that damage from UV radiation appears when there has been an abrupt increase in temperatures accompanied by a drop in humidity, especially when wind is also present. They note that hot, dry air allows more direct UV rays to reach the fruit. Although most varieties of blackberry and raspberry are susceptible to white drupelet syndrome, 'Apache' and 'Kiowa', and the 'Caroline' red raspberry seem to get the disorder more frequently.