Red Maple - 100 Most Common North American Trees

Pest information courtesy of USFS Fact Sheets:

Insects: Leaf stalk borer and petiole-borer enters the leaf stalk just below the leaf blade and defoliates. Serious injury to a healthy tree is rare.
Gall mites stimulate the formation of growths or galls on the leaves. The galls are small but can be so numerous that individual leaves curl up. Galls are not serious, so chemical controls are ususally not needed.
Aphids infest maples. High populations can cause leaf drop. Another sign of heavy aphid infestation is honey dew on lower leaves and objects beneath the tree.
Perhaps the most common is cottony maple scale. The insect forms a cottony mass on the lower sides of branches. Scales are usually controlled with horticultural oil sprays.

Diseases: Anthracnose can be a problem in rainy seasons. The disease causes light brown or tan areas on the leaves.
Girdling roots growing around the base of a maple trunk rather than growing away from it can choke the trunk. Girdling roots are detected by examining the base of the trunk. The lack of trunk flare at ground level is a symptom and treatment can be as harmful as the problem.
Scorch can occur in maples during periods of high temperatures with wind. Trees with poor root systems encourage scorching. Scorch symptoms are light brown or tan dead areas between leaf veins.
Tar spot and a variety of leaf spots cause some concern among homeowners but are rarely serious enough for control.

More on Tree Insects and Disease