Just What Is a Gall?

— Written By and last updated by Nancie Mandeville
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Have you seen any abnormal growths or swellings on the trees or shrubs in your landscape? Often I receive calls or have samples brought in to the N.C. Cooperative Extension of Union County office because folks are concerned that it may be a disease of some sort that could harm their plants. Those growths or swellings are most often a gall which is caused by insects or other organisms that result in abnormal cell growth and development.

eyespot galls on red maple leaves

According to  Renee Strnad, Environmental Educator at NC State University, galls are formed when insects release chemicals into the plant. The chemicals manipulate the way the plant grows, altering its structure to benefit the insect. The chemicals may cause changes that provide nutrients or shelter needed for survival. Galls come in many shapes, colors, sizes, textures, and longevity. Many are so characteristic that one can determine the causal insect or organism just by looking at the features. While there are many kinds of gall-forming insects including aphids, wasps, midges, beetles, sawflies & adelgids, they are typically species specific, meaning that they cause gall formation in a specific species or group of plants. For example, the larvae of the maple eyespot gall midge (a small fly) form round, often reddish, “bulls-eye” patterned galls on the leaves of red maples). No other organisms will cause that and the midge typically does not infest other tree species. Galls can be seen on any part of the plant: leaves, flowers, twigs, and branches, shoots, main stems, and buds. Though the appearance of galls can be alarming, the damage is typically only aesthetic. Because they cause little or no harm to their host plant, management is typically not recommended.

Join the Extension Master Gardener℠ volunteers of Union County for their monthly educational meeting on May 16, 2019, at 7 p.m. at the Union County Agriculture Center. The speaker will be Mary Roberts of Windcrest Farm and her topic will be 10 Tips for Terrific Tomatoes.