Dryberry mite—Phyllocoptes gracilis
This eriophyid mite (family Eriophyidae) is a pest of blackberry and raspberry fruit. Note that numerous species of mites can occur on plants.
Because eriophyids are minute, the presence of dryberry mite is diagnosed primarily by the characteristic damage symptoms on fruit as described below under "Damage."
The mites are carrot or wedge shaped and pale brown to pale yellow or whitish. Adults are about 1/100 inch (0.25 mm) long. A dissecting binocular microscope or a hand lens of at least 20× is needed to see them. Deutonymphs (first-stage immatures) are about one-half the length of adults. Protonymphs (older immatures) are about the same length as adults. Adults and nymphs have 4 legs at the head (wider) end of their body. The oval eggs are translucent to white and about one-fourth the length of adults.
Dryberry mite develops through four life stages: egg, protonymph, deutonymph, and adult. Fertilized adult females overwinter in buds and in axils, the crevices where bark and buds touch.
In spring, the mites become active. As buds swell and burst, the mites enter the expanding leaf buds and females lay eggs. During her 1-month life span, an adult female can lay about 80 eggs, which hatch into both female and male mites. All developmental stages are present during the summer and early fall. During the growing season, the mites may be found on fruit and leaves. In late fall and winter, the mites aggregate in colonies in or near buds on the canes.
Development from egg to adult takes 1 to 2 weeks, the quicker at warmer temperatures. There are many overlapping generations each year.
Mite feeding causes drupelets to become dry and hard and fail to develop their mature color. This makes berries unappetizing. Mite feeding can also cause yellow leaf spots that become reddish and necrotic. Note that redberry mite (Phyllocoptes gracilis) causes similar damage to fruit of blackberry and rarely raspberry and can also be managed as below.
Predaceous mites such as Phytoseiulus persimilis may help to reduce the abundance of dryberry mite and redberry mite. To improve the potential effectiveness of biological control, control ants, minimize dust (e.g., periodically hose off plants), and avoid the application of broad-spectrum, persistent insecticides and miticides for all caneberry pests. See Protecting Natural Enemies and Pollinators for more suggestions.
At the time mite damage to fruit becomes apparent, it is too late for control to be effective. If fruit damage the previous season was intolerable, spray a micronized or wettable sulfur on buds and terminals at the delayed-dormant stage, after buds swell but just before they open. This is the time when the overwintered mites become active and miticide application can be most effective. Azadirachtin, narrow-range or horticultural oil, or neem oil can be sprayed at two to three week intervals after the green fruit stage. Do not apply oil within 1 month before or after a sulfur application and vice versa or plant damage can occur.
For more information see Dryberry Mite Acari: Eriophyidae Phyllocoptes gracilis (PDF) from Oregon State University, Dryberry Mite (Phyllocoptes gracilis) Insects and Invertebrates from Washington State University, and The Eriophyid Mites of California from the University of California.
Dry, pale raspberry drupelets caused by feeding of dryberry mite.
Blackberry drupelets that remained red due to feeding of the redberry mite, a pest similar to dryberry mite.
A caneberry bud and axil with an arrow marking where the mites overwinter and delayed-dormant spray should be targeted.