WSU Whatcom County Extension

Integrated Pest Management for Blackberries

Redberry Mite

(Acalitus essigi)

Insects and Invertebrates

 

Redberry Mite

 

Symptoms

Redberry mites are a pest of all blackberries, but are most damaging to late-maturing cultivars, such as ‘Thornless Evergreen’ and ‘Chester’. The mite feeds at the core, stem, and base of drupelets. During feeding, the mite injects a toxin that prevents proper drupelet development. Affected drupelets usually remain hard, green, or bright red and result in unmarketable fruit. Some fruit may be partially affected allowing only part of the berry to ripen. There may be anywhere from one hundred to several hundred mites in a single berry. If not controlled, the mite can spread from a few infected canes to sizable portions of a planting in the next season causing a severe loss in total yield.

 

Identification

Redberry mites belong to a group of microscopic mites known as eriophyid mites. They have two pairs of legs and are 1/50 inch long. The adult is wormlike and translucent white.

 

Life History

The mites overwinter in bud scales or deep in buds where they are well insulated and protected. In spring, the mites move onto the developing shoots. Later in the season, the mites move into unfolding flower buds, flowers, and developing drupelets of the berries, especially near the bases and around the core of the fruit.

 

Redberry Mite

 

Monitoring

Watch for fruit that never ripens and remains hard. Use a 10 to 20x hand lens or dissecting microscope, to verify mite presence by inspecting at the base of drupelets showing symptoms. Scout 3-5 sites (depending on field size) and evaluate 10-20 hills, spaced 3-5 hills apart. Record the percentage of infested hills at each site.

 

Thresholds and Management

No threshold or tolerance level available.

A program of preventative dormant sulfur applications should be implemented the following early spring if mites are found at significant levels. Monitor that year’s developing fruit to assess efficacy of preventative sprays.

 

Resources

Washington State University Extension, Small Fruit Pest: Biology, Diagnosis and Management
http://cru.cahe.wsu.edu/CEPublications/eb1388/eb1388.pdf

University of California Davis, UC IPM Online, Caneberries: Redberry Mite
http://www.ipm.ucdavis.edu/PMG/r71400111.html

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WSU Whatcom County Extension 1000 N. Forest St., Suite 201, Bellingham, WA 98225 (360) 778-5800 whatcom@wsu.edu