Plant galls occur in an intriguing variety of strange shapes, textures and colors. Some are asymmetrical, bumpy, or warty, where others are smooth and round. Some galls have thick growths of fuzz, hair or spines. Moss galls (or galls in general) do not harm the plant, unless there are quite a few of them. They need the plant to live to also be able to live.
Galls result from a complicated interaction between two living organisms. The gall-maker (insect, disease or mite) causes the plant to modify its growth into a special dwelling that surrounds the gall-maker. In the case of mossy rose galls, it is a small cynipid wasp called, Diplolepsis rosae.
The Mossy Rose Gall Wasp emerge from the old galls in early spring (April to May) as the weather turns warmer. Females lay eggs for about 3 weeks in the dormant buds of roses, preferring the rugosa line. Larvae hatch and as they feed on the buds, chemicals in their saliva causes the leaves to distort and grow large galls. The larvae live within the gall, all the while feeding and growing to finally emerge the next spring. There is one generation per year.
There’s really no pesticide that can cure this. If you can’t handle seeing them on your rose, prune them out.
© Ilex – Midwestern Plant Girl