Spider mites are an extremely small pest, and generally appear as a brown, red, or purple specks on the underside of leaves. Mites infest leaves and cause the leaves to appear speckled with yellow spots or wilted and curled. A fine silken webbing can sometimes be seen on the underside of the leaves. Intense infestations during hot, dry weather can cause leaf drop.
To confirm if the tree has a spider mite infestation, closely inspect the undersides of leaves for small insects, the size of ground pepper. You may need to use a small magnifying glass to see the spider mites adequately. Another way to examine for spider mites is to take a sheet of white paper and hold it under a group of leaves and give the leaves a few sharp taps, to shake some of the spider mites loose. On the white paper the spider mites can be seen easily.
Spider mites damage trees by sucking sap from the underside of the leaves. The bite marks appear as a yellow speckled pattern on the top and bottom of the leaf. As the season progresses and the temperature becomes hotter and dryer (above 70 degrees F), the population of spider mites will increase exponentially and can rapidly defoliate a tree, especially if the tree is having trouble taking up water during drought periods. Often, a tree being attacked by spider mites appears to be dripping, because as insects suck the sap from the leaves, they produce a liquid honeydew, which is the undigested sugars. The honeydew gives the leaves a sticky feel and a wet look.