On a walk this past weekend, I saw some oak galls. Sometimes called oak apples or oak potatoes, oak galls are abnormal growths on oak leaves, twigs, or stems that are made from the plant tissue itself by parasitic wasps.
Galls can be made by fungi, bacteria, mites, or other insects. And they appear on other plants besides oaks. The gall-making insect produces growth-regulating chemicals that cause the plant tissue to grow unnaturally and abnormally. The insect takes advantage of plant tissue that is growing at a very fast rate in the spring, producing the growth chemicals that cause the plant tissue to form the gall.
Insects that form galls are either larvae that have already been laid on the plant, or an adult insect that has recently laid eggs. The larvae develop inside the gall, feeding first on the host plant’s nutrients until the gall is fully developed, and later on the tissue of gall itself.
Most gall wasps spend at least 2 years in the gall before reaching maturity and leaving the gall. Adult wasps usually overwinter in trees near the host plant. Gall wasps are in the family (Cynipidae). I’m not sure exactly which type of gall wasp made this gall.
In general, galls are harmless, although sometimes they can cause premature leaf drop or halt photosynthesis (the plant’s food-making process). Most homeowners think they’re ugly, though, and worry about damage to their plants. But chemicals or pesticides are rarely suggested to control galls–the risk isn’t worth the return.
After all, it’s just “nay-cha,” as they say here in Little Rhody.