By Ken Johnson
Jumping oak gall can be a common occurrence on trees in the white oak group (white, bur, etc.). Jumping oak galls are caused by a small stingless wasp. The galls are round button-like discs that are formed on the underside of leaves. The galls will cause the upper sides of the leaves to become lighter and color and blister. If leaves are severely infested the tips may turn brown. These leaves will often begin to curl and fall from the tree. In rare cases trees can become defoliated. The blister is often surrounded by a yellow halo. They get their jumping name from when the galls fall to the ground. The larvae inside will move around inside the gall causing it to ‘jump’ around.
In early spring female wasps will lay eggs in the developing leaf buds of a tree. The eggs will hatch and the larvae will feed on the leaves and the tree will form a gall. The gall is formed as a response to chemicals in the saliva of the larvae. The larvae will remain inside of the gall and feed. In early summer the galls will drop from the leaves and fall to the ground. The larvae will become a pupa and overwinter in the ground. In early spring the wasps will chew their way out of the galls and start the cycle again.
While damage can at times be severe it is rarely fatal for healthy trees. Often symptoms can be bad for a few years. As the populations of the gall wasp subside, due to a buildup of natural enemies, the symptoms will become less severe. Because of this, and the fact that the larvae are protected by galls, chemical controls are generally not recommended. If your trees are affected by jumping oak gall maintain your trees health by mulching around the tree, making sure it has adequate water, avoid damaging the tree with lawnmowers and trimmers (another advantage of mulching around a tree), and fertilizing in the spring in necessary.