My small oak tree has several leaves that have red bumps on them. What is this?
They are very small but numerous.
Answer
The bumps on the oak leaves are most likely Oak galls. Tiny female wasps or flies lay eggs on the leaves, branches or trunks. The eggs hatch into legless grubs. The gall forms around them as the insects feed and develop, they finally leave to start the process again. It is thought that the gall growths are a reaction to the chemicals the insects secrete or inject during feeding. Each insect causes its own uniquely shaped gall, either round, flat, spiny or star shaped. Rarely do they cause damage though the galls don't disappear after the insect
leaves. If the problem is severe, you can try to reduce the population by removing and destroying the affected limbs. Remove early in the season, before the adults emerge.