Question
Growth on Birch Tree L
Dear Jim, I essentially live in the woods in the Pocono Mountains of NE PA. Attached is a picture of the leaves of (what I think is a small birch tree) in my yard. There are several small trees like this one that have these growths on their leaves. Can you ID this for me? I am very curious. Thank you very much. -- Jack
AnswerThese are galls caused by more than likely a mite feeding on the leaf or laying eggs on the leaf. the mite secretes a chemical than causes the leaf cells to expand to cover the eggs.
Galls are abnormal growths of plant tissue that form in response to a wound, infection by various microorganisms, or the feeding and egg-laying activity of certain Insects and mites. Galls occur on almost any plant tissues. The most common are leaf, stem and flower galls produced by Insects and mites.
Galls often are unusual in form, conspicuous, and frequently cause considerable concern. Galls produced by Insects and mites rarely cause serious threat to plant health. Most gall-maker populations fluctuate from season to season. The occurrence of many in one year usually is followed by few the next.
Galls are produced by plant cells stimulated to abnormal growth. Galls from Insects and mites usually result from chemical secretions produced during feeding or egg laying. The chemicals act like natural plant growth hormones. Galls also may form following mechanical injury from insect feeding.
Although galls are conspicuous and unattractive, they rarely do any real damage to plants. Gall-making is cyclical and problems often subside with natural controls. Furthermore, once galls start, formation is largely irreversible. Under most circumstances, control is not recommended. Occasionally, heavy infestations that occur repeatedly over several seasons may slow the growth of the plant or make the appearance unattractive.
The eriophyid mites and a few gall-making Insects that overwinter on the plant may be controlled with dormant oils. However, most galls are produced by Insects that move to the trees as new growth develops in the spring. They can be controlled only with sprays that cover the leaves during the egg-laying period. Repeat applications often are needed.
I see no reason to try to control the galls. The population of the mites varies greatly from year to year so next year you might not have any. The galls will not harm the overall health of the tree.
