How to Manage Pests

UC Pest Management Guidelines

DESCRIPTION OF THE PEST

The redberry mite is a perennial pest of both cultivated and wild blackberries but is not an economic pest of raspberries. These mites belong to a group of microscopic mites known as eriophyid mites. This eriophyid mite has two pairs of legs; it can be seen with a 10 to 20X hand lens but is best seen with a dissecting microscope. The adult is wormlike and translucent white.

Redberry mites overwinter in bud scales or deep in buds. As shoot growth develops in spring, the mites move onto the developing shoots. As flower buds appear, the mites work their way into the unfolding buds, into the flowers, and down among the developing druplets of the berries, especially near the bases and around the core of the fruit.

DAMAGE

Fruit infested with redberry mites do not develop normally colored druplets. Affected druplets usually remain hard and have a green or bright red color. The fruit is unmarketable. Fruit partially affected may have some druplets remain red and hard with the remaining druplets developing proper ripening. If not controlled, redberry mite can spread from isolated infestations to sizable portions of a planting in the next season. Very high populations can result in significant crop loss. The pest is most damaging to late-maturing blackberry cultivars.

MANAGEMENT

The best time to control redberry mite depends upon variety grown and miticide that will be used. Note that oil and sulfur products should never be tank-mixed because of the risk of phytotoxicity. If oils are used after or before sulfur products, be sure to observe all recommended label precautions.

Lime Sulfur
Timing of lime sulfur applications depends upon variety grown and redberry mite severity. For blackberry varieties that retain a leaf canopy through the winter, begin lime sulfur applications at bud break and continue at 3-week intervals up to 12 days before the start of harvest. For blackberry varieties that naturally defoliate over the winter, apply lime sulfur before buds break dormancy but then not again until canes have a full leaf canopy and first bloom appears.

Horticultural Oils
Horticultural oils, such as Natur'l Oil and Golden Pest Spray Oil, when used at the rate of 1.2 to 2% volume to volume, applied after green fruit or first pink fruit stage in four consecutive applications spaced 2 or 3 weeks apart give significant control of redberry mite, while causing less harm to fruit yield than sulfur sprays.

Complete plant canopy coverage is important when using horticultural oils, so the minimum amount of water carrier should be 50 gallons per acre.

The potential for phytotoxicity of oil product and/or oil product mixes has not been fully evaluated for all blackberry varieties in all growing areas. Small plot tests are prudent to determine safety margins of particular blackberry varieties for specific environmental conditions in different growing areas.

PUBLICATION

UC IPM Pest Management Guidelines: Caneberries
UC ANR Publication 3437
Insects and Mites
E. J. Perry, UC Cooperative Extension, Stanislaus County
M. P. Bolda, UC Cooperative Extension, Santa Cruz County
L. J. Bettiga, UC Cooperative Extension, Monterey County
Acknowledgment for contributions to the insect and mite section:
R. M. Tyler, UC Cooperative Extension, Santa Cruz County
E. Show, Driscoll Strawberry Associates Inc., Watsonville, CA

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