Yellowish in color tinged with red. Control flies that emerge from galls in October with a general-purpose insecticide. Spherical galls are found on leaves and twigs. Control is not usually necessary. Galls form on the leaves and later on the stems.
Galls vary greatly in shape but are more or less tuber-like.
They deform the branches. Cut and burn all twig galls before the first of March. Insecticide spray may do more harm than good by killing beneficials. Found on the elm leaves. Treat with malathion or horticultural oil before the buds open.