How to Manage Pests

UC Pest Management Guidelines

DESCRIPTION OF THE PEST

The walnut blister mite occasionally occurs in walnut orchards. Adult mites are very small and cannot be seen without a 14 to 20X hand lens. They have a white, slender, striated body with a few long hairs. Immature forms resemble adults but are smaller. Eggs are spherical and pearly white.

DAMAGE

Blister mite feeds on the lower surface of leaflets, causing characteristic blisterlike swellings on the upper surface of leaflets. It occurs in yellow to orange felty masses in depressions on the underside of blistered leaves. Later in the season, these areas turn brown. The blisters can be large and unsightly, but damage caused by the walnut blister mite is primarily aesthetic.

MANAGEMENT

Blister mites do not cause economic damage to walnut trees, and no control is necessary.

PUBLICATION

UC IPM Pest Management Guidelines: Walnut
UC ANR Publication 3471
Insects and Mites
C. Pickel, UC IPM Program/UC Cooperative Extension, Sutter/Yuba counties
J. A. Grant, UC Cooperative Extension, San Joaquin County
W. J. Bentley, UC IPM Program/Kearney Agricultural Center, Parlier
J. K. Hasey, UC Cooperative Extension, Sutter/Yuba counties
W. W. Coates, UC Cooperative Extension, San Benito County
R. A. Van Steenwyk, Insect Biology, UC Berkeley
Acknowledgment for contributions to Insects and Mites:
W. H. Olson, UC Cooperative Extension, Butte County
L. C. Hendricks, UC Cooperative Extension, Merced County
G. S. Sibbett, UC Cooperative Extension, Tulare County

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