Question of the Week: Bumps on Aspens

Q: I have aspen trees with numerous bumps on the branches. What are they?

A: These bumps are known as poplar twig galls, a common occurrence on aspen trees. They are caused by the poplar twig gall fly, which lays eggs in the developing stems. The larvae hatch and feed within the stem, causing the swollen galls.

Fortunately, these galls do not harm the health of the tree. There is no need for control or prevention, although birds can naturally help keep them in check.