Gall mites cause growths or galls to develop on the leaves of red maple trees. Although small in size, these galls can grow in such large numbers that affected leaves curl up. Several types of gall mites attack the red maple, including maple bladder-gall mites and maple spindle-gall mites. Gall mites cause little damage to well-established red maple trees, but they give the trees an unpleasant look and can cause great stress to small or new trees.
Things You'll Need
Dormant oil or liquid lime sulfur
Pesticide containing diazinon or sevin
Remove damaged leaves by hand to reduce mite populations. Each gall contains one feeding adult mite and eggs if the adult mite is female.
Apply a dormant spray before bud break in early spring to reduce the number of gall mites that overwinter on the tree. Use dormant oil or liquid lime sulfur and spray it when temperatures are above 40 degrees and you don't expect freezing temperatures within 24 hours.
Apply a pesticide containing diazinon or sevin after the leaves start developing at about half of their normal growth rate. Spray the pesticide as the new leaf buds are opening because pesticide application will have little effect once the galls have formed. Follow manufacturer's instructions on application rate.
Release gall mite predators to organically get rid of gall mites from your red maple. Natural enemies of gall mites include green lacewings and ladybugs.
Leave gall mites alone if the tree's appearance doesn't bother you. Even in severe infestations, gall mites don't significantly affect the tree's vigor and only causes temporary injury on well-established trees. The tree leaves have to be growing for galls to form, so mite activity stops as soon as new growth ceases. Grow resistant maple cultivars such as Norway maples instead of red maples.
Don't use these sprays if you see any new leaves on the tree because dormant oil can damage actively growing leaves and twigs. (ref 6) Lime sulfur will stain cement, stone and wood materials.