Vein Pocket Galls on Oak Trees
Alien looking growths on your tree’s leaves…
Sometimes what looks like a plant disease can actually be the work of tiny insects. Galls are deformities on the leaves of plants that are caused by insects that lay eggs in the leaves. While gall formation is not totally understood, it's thought that plant hormones react to saliva from the insects and cause leaf cells to grow in exagerated ways.
In the photo, you'll see swollen ridged tissue along the mid-vein of this oak leaf. This is called a vein pocket gall and is caused by the vein pocket gall fly (Macrodiplosis quercusoruca). It lays its eggs on the undersides of oak leavs in spring. As the larvae emerges and begins feeding on the leaves, plant hormones react and the ridges form along the center of the leaves.
Chemical control of these kinds of galls is very difficult. Your best bet is to focus on the long term health of the tree by boosting its immune system through proper watering and feeding.