The Q&A Archives: holes in oak leaves

Question: My Oak Tree looks like someone shot buckshot into the leaves. There are millions of holes in the outer leaves. Also, some leaves have nodules in them and some leaves look like someone put a line of ruffles in the middle of the leaf. What is causing this and how do I treat it?

Answer: It sounds suspiciously like leaf galls. Galls are abnormal plant growth or swellings com-prised of plant tissue. Galls are usually found on foliageor twigs. These unusual deformities are caused byplant growth-regulating chemicals or stimuli producedby an insect or other arthropod pest species. Thechemicals produced by these causal organisms inter-fere with normal plant cell growth.

There are a variety of gall-forming species of small wasps that commonly infest oak, Quercus spp., trees. Leaf galls rarely affect tree health so control is rarely justified. However, an application of carbaryl (Sevin) at bud break may reduce infestations of some galls. It is difficult to spray moderate to large trees without special equipment and the necessary protective clothing to protect the applicator from spray drift.

Since the damage is mostly aesthetic, I'd leave the tree alone and rake up the fallen leaves. Eventually the problem will subside on its own.

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