Mossy rose gall wasp (Diplolepis rosae)
Spiny rose gall wasp (Diplolepis bicolor)
Pest description and damage The mossy rose gall wasp and spiny rose gall wasp are both tiny (0.12 to 0.24 inch in length) wasps which induce galls that may measure from 2 to 4 inches in diameter to form on the leaves. Galls may form on leaves, stem, bud or root. The larva of the wasp is inside the gall. The appearance of the two galls is different. The mossy rose gall wasp causes a cluster of hard, kernel-like cells to form on the rose stem or leaf, with moss-like filaments all over it. The spiny rose gall has a spherical hard body with many spiky protrusions. Other gall wasps cause buds to enlarge and harden.
Biology and life history The insect overwinters as a larva in the gall, and in early spring the adult wasp matures and chews out through the gall. It looks for expanding leaf tissue to lay eggs on. The eggs hatch and the feeding of the larvae induces the gall to form around it. There is one generation per year.
Pest monitoring In late winter, place a few galls in a baggy and leave outside in a protected location. Check regularly for the emergence of the first gall wasps. Then confirm emergence holes in galls on the plants.
Cut out galls when they are still green and fresh and before gall wasps have emerged and flown away. Adult emergence is in spring, so late summer and winter removal of the galls works best. Old galls have holes and become brown and matted.
See Table 3 in:
Chemical Control of Landscape Pests
For more information
See "Gallmakers" in: