Question
I have several Gamble oak on my property and there are these wart like things on the spines of the leaves. The color of these "things" range from yellow to red. Most of what I see are on the young trees. Mature ones seem to be not affected. What is it and how can I control it. I have been to the local nursery and they are clueless.

Answer
Thes are called leaf galls. These are oak leaf galls made by an insect a small wasp usually. The insect lays its eggs on the leaf and secretes a chemical that causes the cells of the leaf to expand and cover the egg making a gall. the galls will not harm the tree's health but if there are many may cause the tree to drop its leaves sooner than normal. There is not need to control these insects.

Gall-forming insects include adelgids, phylloxerans, psyllids, gall midges, and gall wasps. Of the more than 2,000 galling insects in the United States, over l,700 are gall midges or gall wasps.

Galls are abnormal growths of plant cells formed in response to egg-laying by adult insects or feeding by immatures. Eggs are usually laid in actively growing plant tissue. The irritated plant tissue quickly surrounds the egg or immature insect, and protects and provides food for the gall-maker until it matures. Gall-makers may live in individual or communal chambers inside the gall.

The shape of each gall depends on which insect caused it to form. They may look like tiny blisters, round balls, tubes, or folded leaves. The gall surface may be smooth, hairy, or covered with spines.

They may cause the leaves to fall a little sooner than normal. I would not worry with them the population will vary greatly from year to year and next year you may not see any galls. There is not practical control measures and really none is needed.