In the early spring, the surfaces of tree leaves develop small spherical growths, called galls. The small special growths are often a light yellow, green, red, or brownish colour and are normally on the top surface of the leaves. Depending on the variety of gall, they can be created as an egg nest or by a toxin injected into a leaf.
Galls are identifiable by small round balls or bumps that grow on the leaves, twigs, and leaf stems of trees. They can also appear as a wide variety of abnormal growths, in a variety of shapes on leaves, twigs, or branches. Infected branches may be discoloured or distorted and drop leaves prematurely and, in some cases, the infected branches die.
In many cases, Galls are created by tiny mites that bite into the underside of the leaf and then inject the leaf with a growth-promoting substance that creates the spherical shaped growth. The circular ball, or gall, encloses the mite, and the female mites lay their eggs in the gall.
Once the gall is formed there is no way to eliminate the balls in the current growing season. However, to help control gall outbreaks, severely infected branches can be removed. Branches and leaves that fall to the ground should be collected and removed.
During the growing season, trees can be sprayed with Bug Buster Pyrethrin Insect Spray or Take Down Garden Spray, to help reduce the mite population and prevent the tree being attacked by other insects that are drawn to weakened trees.
In the fall, the tree should be sprayed with Horticultural Oil Insect Spray, ensuring a good coating is applied to all the branches and the trunk. This prevents the over-wintering of mites and other insects on the bark.
The following spring, just before bud break and again after the leaves start to form, the tree should be sprayed again with Bug Buster Pyrethrin Insect Spray, before the insects enter the leaves and begin to form the galls.