New ISU Extension and Outreach Guide Provides Information on Insect Galls

A new, updated guide has been added to the ISU Extension Store. “Insect Galls on Trees and Shrubs” (ENT 0039) has been revised by extension entomologists, complete with color photos and descriptions.
Insect galls are distinctive swellings or abnormal growths of plant tissue that are caused by the presence of an insect and mite. There are hundreds of unique galls caused by insects and mites, formed on a variety of plants, in broad ranges of sizes, shapes, colors and textures. They can be found on leaves, stems, twigs, branches, trunks and roots. With the wide array of possible diagnoses, this updated guide is an important tool for homeowners and land caretakers who may not have seen such plant injuries before.
While galls might be concerning to homeowners, they do not generally affect the health and vigor of trees and shrubs. Though they are unsightly in appearance and can result in occasional leaf drop or stem deformation, galls are generally not the cause of tree decline or death. Once formed, galls cannot be controlled, and insecticide treatments are not helpful. This resource serves to help homeowners identify gall occurrences in their trees and/or shrubs.
“Insect Galls on Trees and Shrubs” is available for free PDF download through the ISU Extension Store and on the Horticulture and Home Pest News resources tab. If unsure of the type of gall you are finding on your plant, contact the Iowa State University Plant and Insect Diagnostic Clinic for assistance.


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