Eriophyid Mites

• Eriophyid mites are 1/100-inch long, according to Washington State University. Mites are able to overwinter or go dormant on dead debris when weather conditions are hot and extremely cold. As the temperatures rise in the spring, mites come out of dormancy to lay eggs and feed off of maple trees' leaves. These pests suck up the nutrients from leaves. This type of feeding causes the damage on maple trees.
  
  

Symptoms

• Gardeners may notice their maple tree leaves form red bumps or velveting galls on the surface of both the underside and top of leaves, according to the University of Minnesota. Eventually, these bumps may inhibit the maple tree's ability to photosynthesize. Maple trees can withstand a large population of mites without declining in health. However, the damage is aesthetically unpleasing for the gardener. Removing the diseased areas and treating the mites will restore the look of the maple tree.
  
  

Chemical Control

• Spray your maple tree with dormant application of oil in the early spring or before bud break, as suggested by the University of Minnesota. The oil applications must be timed when the adults are actively feeding on the maple leaves. You can also use a pesticide that contains carbaryl. Avoid spraying the tree with a broad spectrum herbicide, because it can actually worsen your mite problem. Broad spectrum herbicide will kill off the mite's natural predators.
  
  

Pruning

• Prune off infected leaves from your maple tree. Use a pair of bypass shears to clip off any bumpy leaves. Rake up the diseased debris underneath the maple tree. Burn or throw away the debris. Avoid placing the debris in your compost or you can spread the mites to other areas of the yard and infect other trees. Provide the maple tree with water and fertilizer to help the tree grow healthy foliage that it may have lost from the infestation.