What Are White, Round, Sticky Growths With Brown Spots on Oak Trees?

• The development of white patches and brown spots on the leaves of an oak tree signifies several potential problems including tree disease and insect activity. In order to properly treat the problem, a homeowner must first identify the problem. In many cases, a local agricultural extension office can help properly identify tree pests and diseases as well as develop a treatment plan. Some potential causes of white growths and brown spots include a lacebug infestation, oak leaf blister and leaf hoppers infections.

Lacebug Infestation

• Sucking insects, like the lacebug, cause the development of white and brown patches to develop on the leaves of the oak tree. The secretions left behind by the lacebug may give these spots a white, sticky texture. Lacebugs feed on the top of the leaves, leaving behind white spots where the leaf tissue is gone. A common sign of infestation is when you see these white spots paired with black spots underneath, as lacebugs lay clusters of eggs below the leaf, according to the University of Illinois Extension. Oak trees grown in hot climates and planted in full sun are more likely to develop lace bugs than those planted in shady, cooler locations. The use of contact insecticides helps treat the lace bug infestation. To be most effective, insecticides should be sprayed directly on the bugs, according to the University of California Davis. Most types of insecticides effectively treat lacebug infestations; contact your local agricultural extension office to determine which insecticides are recommended in your area.

Oak Leaf Blister

• Oak leaf blister, a fungal disease, most commonly causes the development of spots on the leaves of oak trees. Most often, these spots appear as a light green or brown color and generally do not feature a sticky texture. However, it is important to rule out the presence of oak leaf blister when treating leaf spots on an oak tree. Oak leaf blister causes the development of concave, green spots, which eventually thicken and turn brown, according to the Alabama Cooperative Extension System. In severe cases, a white to gray fungus may develop on the underside of blistered leaves. Often, oak leaf blister fungi attacks similar locations. In areas where oak leaf blister occurs, treat trees with a lime-sulfur fungicide prior to the growth of new leaves, suggests North Dakota State University.

Leafhoppers

• Like the lace bug, leaf hoppers commonly cause the development of white, sticky spots on the leaves of the oak trees, according to the University of Illinois Extension. White spots that seem to move are commonly active bugs, as many of them are about 1/8-inch long and usually white or green. Leafhoppers dine upon the upper surface of the leaf, leaving behind white spots of dead tissue. As leafhoppers feed, they extract the sap from the leaves, leaving behind a puckered blister. Sticky residue on the blister may be caused by the leafhopper's natural digestive enzymes. Systematic insecticides such as acephate, disulfoton and imidacloprid are applied directly onto the tree. As the leafhoppers feed upon the tree, these insecticides kill leafhoppers and other sap sucking bugs, according to the Utah State University Cooperative Extension.