What are these?

Asked October 13, 2015, 11:06 AM EDT

We have had thousands of these falling from our oak trees this fall. What are they? What should I do about them? Will they harm the trees next year? The leaves started looking brown and shriveled on some branches in August. Is this just a bad year for this to be happening?

Linn County Iowa oak galls

1 Response

The objects in the photograph appear to be galls. There are many different types of galls. The galls in the photo may be the woolly oak leaf gall.

Galls are abnormal growths of plant tissue induced to form by mites, insects, or other small organisms. They are common on trees. While galls may be unsightly, they do not cause serious harm to established trees.

Insect and mite populations vary from year to year. As a consequence, gall populations also vary from year to year.