I picked some brown, golf ball-size...

Question

I picked some brown, golf ball-size, fuzzy growths off my rosebush the other day. When I cut one open, I found a bunch of little white worms inside, each in its own separate chamber. What are they, and what harm will they cause my roses?

Answer

Sounds as if your roses are infested with wasp galls—odd plant growths, almost like tumors, that serve as homes to the larvae of cynipid wasps, more commonly known as gall wasps. Several different types of gall wasps may be living in these creature condos,” parasitizing one another. The wasps don’t sting and don’t hurt rosebushes much beyond aesthetic damage. Once mature, they even dine on aphids, which is beneficial. But if you have a lot of galls, they can harm the plant by leeching nutrients away from it. Pruning is the best defense against them. Do it in early spring, before the wasps emerge, or in late fall, after the leaves have dropped.”