European Red Mite, Panonychus ulmi (Koch) and
Twospotted Spider Mite, Tetranychus urticae Koch

I. Introduction, Hosts, Description, Biology and Monitoring for these pests are discussed in the apple section.

II. Injury: Mites typically do not become abundant and injurious to peach and nectarine until mid-to-late summer. Feeding occurs on leaves and results in the removal of chlorophyll which gives the foliage a gray or bronzed appearance. This feeding, probably because it occurs late in the season, does not appear to have a detrimental impact on the quality and quantity of fruit production in the same year. High mite populations can result in premature leaf drop which could increase tree susceptibility to winter injury. Other long term or carryover effects from one season to the next have not been adequately investigated. Mites are often most troublesome during the harvest period by being a nuisance or irritant to pickers.

III. Monitoring: Follow mite densities during the season by counting mites per leaf with a hand lens or leaf-brushing machine. Take 10-40 leaves from the canopies of 10 trees (use the larger number in spring, when mites are harder to detect). Action thresholds are only provisional on peach and nectarine. However, recent research has shown that peach is only about half as sensitive to mite feeding as apple. Therefore, use an action threshold of about 10 mites per leaf early in the season, and 20 mites per leaf late in the season. Thresholds may need to be adjusted based on the sensitivity of pickers to mites.

See Univ. of California links to ERM on peach and nectarine.
Additional Reading:
This is taken primarily from a chapter by H. W. Hogmire and D. F. Polk on peach indirect pests, reprinted with permission from Mid-Atlantic Orchard Monitoring Guide, published by NRAES, 152 Riley-Robb Hall, Ithaca, New York 14853-5701. (607) 255-7654.
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