Redberry mite
Acalitus essigi
5 host plants
Last updated
On blackberry drupelets, watch for uneven ripening where individual segments remain hard, green, or bright red instead of softening and turning black; this is classic redberry disease caused by Acalitus essigi. Mature-season blackberry cultivars like Apache and Triple Crown experience more damage than early-season types. The translucent white mites are roughly 0.1mm long and require 20-30x magnification to see.
Redberry mites overwinter within buds, then move to developing flower buds. Their feeding releases a toxin preventing drupelets from ripening. Scout flower buds in spring and treat before flowering if redberry disease was severe previously. Sulfur applications during bud development are effective.
Quick Reference
The redberry mite is an eriophyid mite. It is a tiny (1⁄50"), sausage-shaped, yellow mite which feeds primarily on the fruit of blackberries. The symptoms of redberry mite feeding are known as redberry disease. The mites feed between the drupelets (the small sections of the fruit) and at the core of the fruit. Affected fruits are hard and do not ripen normally. They are partly or entirely bright red (sometimes green), rather than black. Redberry mites overwinter in buds and in bark crevices, migrating to green fruit in the spring.