Fact Sheet: Understanding Tree Galls
Overview and Management
Executive Summary
Tree galls are abnormal growths of plant tissue—appearing as bumps, swellings, or protrusions—resulting from the manipulation of a tree’s hormones by external organisms. While their appearance can be alarming, most galls are a natural part of local biodiversity and rarely pose a fatal threat to established trees.
Etiology: What Causes Galls?
Galls are the result of a complex biological “hijacking” of the plant’s growth processes.
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Primary Culprits: * Insects & Mites: The most frequent causes, particularly gall wasps and flies. Larvae develop within the tissue, utilizing the gall for both shelter and nutrition.
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Pathogens: Specific fungi and bacteria (such as the crown gall bacterium) can induce localized tissue proliferation.
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Biological Mechanism: The invading organism releases chemicals—such as saliva or specific growth regulators—that interfere with the tree’s natural hormonal balance, forcing the plant to produce excess cells.
