Gall wasp

Rose species throughout Western Washington develop abnormal swollen growths on stems and branches, created by gall wasp larvae developing inside plant tissue. These woody or spongy galls range from small marble-sized knots to larger nodular formations that girdle or deform stems. You may see exit holes in the galls where adult wasps have emerged. Gall wasps attack Rosa species, hibiscus, and occasionally other ornamentals; heavy galling weakens branches.

Prune out galled stems below affected areas during dormancy and burn or bag the material. Make clean cuts to encourage wound healing. Most populations are naturally controlled by parasitoids; avoid broad-spectrum insecticides. No chemical control is warranted since cosmetic damage is typically the only concern. Focus pruning to remove galls during late fall or winter.