Every year people become alarmed at finding these small, multicolored bumps on the upper leaf surface of their silver maple trees. Control is not effective at this time as the galls have already formed and will not go away. Control is rarely warranted at any time as even trees with every leaf infested with the galls show no injury due to the feeding or gall formation. The small tan larvae feed in small groups in webbed twigs of plums and a few other plants. The larvae have yellow to orange heads with short, prominent, black antennae.
Chemical control is difficult due to the webbing.
Often control is not necessary but if a tree is heavily infested it could be defoliated. In this case, prune out infested twigs and destroy them. The pear slugs can be found feeding on a wide range of plants but seem to prefer cotoneaster. The slimy looking pests are actually the larvae of an insect and not true slugs. They are usually light green to dark green and often have a dark colored dab of fecal material on their back.