Insect Galls
A gall is an abnormal growth on the leaves, stems and twigs, or
flowers of a plant. This abnormal growth is the reaction of the plant to
the feeding damage of an insect or to a toxin injected by the insect during
feeding. Galls come in a wide variety of shapes and colors and are caused
by a wide variety of insects.
The good news is that galls cause very little damage to the health of the plant, therefore, treatment is usually not recommended. The severity of the infestation will vary from year-to-year, so if it is bad one year, it does not mean that it will be a problem the following year. To reduce the insect population, galls can be pruned off.
Eriophyd mites cause bladder and spindle galls on maple leaves. These galls change in color from yellow-green to red as the season progresses. Bladder galls eventually turn black. The leaves may drop prematurely in late Summer or early Fall.
Eriophyd mites also cause a velvet gall on maples and viburnums. These bright red galls form dense, velvety mats on the upper and lower surfaces of the leaves.
The aphid-like insect, adelgid, is the cause of the Eastern Spruce gall found at the base of new growth on a variety of spruce trees. Adelgids also cause the Cooley Spruce gall to form on the tips of new growth on Colorado Spruce trees.
Oak trees exhibit a wide variety of galls on their leaves and stems. Most are caused by a small wasp that lays its eggs on the leaves and stems. Each type of wasp causes its own particularly shaped gall.
Chemical control is recommended only on plants that are infested on a yearly basis and if the plant is showing signs of distress or growth is being distorted. Treatment must be done in the early Spring before galls form. Chemical control is ineffective once the galls have formed.
If you suspect you have galls, bring a sample in to our experts at Bachman's to help you diagnose the problem and determine if any treatment is necessary.
Revised: 03/10/98
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