Oak Apple Gall Wasp

Description

• The oak apple gall wasp (Amphibolips confluenta) produces 2-inch-wide galls on all varieties of oak trees. The galls can potentially grow as large as a golf ball. The outer covering is paper thin with a sponge like interior. New galls are green and gradually grow brown as they age. The wasp does not sting or bother people. About 80 percent of all known gall wasps specifically target oak trees, cites the University of Nebraska Lincoln Extension.

Life Cycle

• The adult oak apple gall wasps start to hatch from the galls during June and July. After mating, the insects drop to the soil where the females burrow into tree roots and lay their eggs. The emerging larvae feed on the roots for about a year before assuming the pupae stage. Wingless female wasps hatch from the pupae and crawl up the tree in spring. The pests find new leaves and lay their eggs in the center vein. The larvae that hatch cause a chemical reaction in the tissue that cause a gall to start growing around the larvae. The galls grow with the larvae that also pupate within the gall and finally emerge as adult wasps.

Damage

• Oak trees, especially scarlet oak, red oak and black oak, are the only hosts of the oak apple gall wasps. The resulting galls invite other parasites and disease organisms to the tree. These organisms find shelter in the gall and damage the tree without harming the larvae inside. Though the oak apple gall wasps are not directly damaging to tree health, the resulting galls can make trees look extremely unsightly. Cases of severe infestation lead to premature defoliation.

Control

• Keeping trees in good health with adequate irrigation, fertilization and timely pruning is among the best preventative measures against infestation. Prune and destroy smaller branches with lighter presence of galls. Insecticides are ineffective in reducing galls or the larvae inside. Though the galls on the foliage fall with the leaves, the ones on the roots or trunks remain on tree for extended periods of time.