Maple gall mites, tiny insects related to spiders, cause unsightly deformation on maple leaves on which they feed. There are three major types: the maple bladder-gall mite, the maple spindle-gall mite and the erineum gall mite. Though the warty galls created by these mites are unattractive, they do very little damage to the trees they inhabit. The main purpose for treatment against maple gall mite is the elimination of the warty growths.
Treat a tree with a known infestation of maple gall mites once the leaves have fallen in late fall. Apply dormant oil or a broad-spectrum pesticide to the tree, completely covering the cracks and crevasses formed by the tree bark. This is where maple gall mites spend their winters.
Treat twigs and buds with dormant oil just before they open, making sure that all buds are thoroughly soaked. Treating maple gall mites while they are hibernating and just before they reawaken will eliminate the vast majority of these insects.
Apply a broad spectrum pesticide once the leaves of the affected maple tree have begun to develop, but before they reach half their mature size. Carbaryl and deltamethrin are now recommended when treatment is deemed necessary.