Blister Mites (Phytoptus spp.)
Figure 1. Blister-like galls from blister mites. Photo by Laurie Kerzicnik, MSU
Apple, crabapple, and pear trees
Figure 2. Blister-like galls on the underside of an apple leaf. Photo by W. Cranshaw, Bugwood.org
Damage and Symptoms
Eriophyid mite feeding creates a “blister” on the leaf surface, and the mites reside within this protected area.
The mites overwinter as adults beneath bud scales. When the buds start to grow in the spring, mites attack the emerging leaves. Their activity increases in the summer, with two-three generations per year.
The mites normally do not affect the health of the tree. If it is just a small portion of damaged leaves, prune and dispose of them. Eriophyid mites are also controlled naturally by predatory mites, predatory thrips, and minute pirate bugs later in the summer.
- Once visible galls are formed, it is difficult to effectively treat blister mites.
- A dormant oil can be applied prior to bud break.
- Neem oil, insecticidal soap, and sulfur are reduced-risk chemical options and can be applied following bud break and during the summer.
- Miticides and insecticides with the active ingredients abamectin, bifenthrin, carbaryl, deltamethrin, malathion, permethrin, and imidacloprid are broad-spectrum insecticides that can be used as a last resort for heavy infestations but are generally not recommended (they often kill beneficial insects and predators of mites, which can increase populations of the blister mites).
- Make sure to follow the label (especially temperature restrictions for applying horticultural or neem oil).
To learn more about the topics discussed on this page, contact MSU Extension arthropod diagnostician Dr. Laurie Kerzicnik. If you suspect an infestation on your property, contact your local extension agent, the Schutter Diagnostic Lab at Montana State University, or the Montana Department of Agriculture.
This fact sheet is also available as a printable PDF (510KB).
Disclaimer: These recommendations are provided only as a guide. It is always the pesticide applicator’s responsibility, by law, to read and follow all current label directions for the specific pesticide being used. The authors and Montana State University assume no liability resulting from the use of these recommendations. The Montana State University Extension Service is an ADA/ EO/AA/Veteran’s Preference Employer and Provider of Educational Outreach.