Redberry mite

Pathogen and disease type
Redberry disease is a physiological disorder caused by the feeding activity of the redberry mite (Acalitus essigi). While referred to as a disease, it is technically an infestation by an eriophyid mite. These microscopic pests reside within the drupelets of the berries, injecting toxins during feeding that prevent the fruit from maturing properly, causing permanent damage to the cellular structure.

Affected crops
The primary host is European raspberry. The mite is particularly problematic for late-season ripening varieties, as the pest population reaches its peak during the time when these berries are forming and maturing. Blackberries are also susceptible, often exhibiting similar symptoms of hardened, unevenly colored, and malformed fruit.

Symptoms and signs of infestation
The hallmark sign of the mite is the uneven ripening of the drupelets. While parts of the berry may turn deep red or purple, other sections remain hard, sour, and unripened (appearing green, pink, or white). Affected berries are woody and bitter, significantly reducing their quality for both fresh market consumption and commercial processing.

Conditions for development and impact
Redberry mites thrive in warm, humid climates, which facilitate rapid reproduction. They overwinter in the buds and bark of canes. The damage is severe because the infestation is often not detected until the berries begin to ripen. In heavy infestations, the entire yield can be rendered unsalable, causing significant financial losses for growers and requiring intensive management strategies.

Control and prevention measures
Effective management relies on integrated pest management practices:

• Planting early-maturing varieties that finish harvest before mite populations peak.
• Rigorous sanitation, including the pruning and destruction of infested canes and debris.
• Application of selective acaricides during the pre-bloom and post-bloom stages.
• Using certified pest-free nursery stock to prevent the introduction of mites into new plantings.