Gall makers

Gall wasps (Mossy rose gall, Diplolepis rosea;
Spiny rose gall, Diplolepis bicolor)

Wasp galls are abnormal plant growths resulting from activity of the tiny, non-stinging cynipid wasps.

Mossy rose gall
Photo 18: Mossy rose gall
Rose galls occur on leaves or stems of the rose plant and are specific to the species of gall maker. The mossy rose gall looks like a mossy sphere. The spiny rose gall is round with many pink spines. Insect larvae develop inside the gall. Stem galls can damage plants above the location of the gall, especially if there are many galls on a particular stem. Numerous galls may stress the plant because nutrients otherwise available for plant growth are used to produce galls.

Control is best done by pruning out galls before the wasps have matured and emerged from the gall. Since adults emerge from the old galls in spring, prune out the galls after the leaves drop in fall, cutting below the gall and above a bud. For leaf galls, pick up fallen leaves. Removing the galls from the garden may not totally eliminate future problems if adult wasps fly in from nearby areas. Timing for insecticidal treatment of these wasps is difficult and not suggested.

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