Ken’s Quick Tip: Oak Galls

Every year I get a dozen or so questions regarding weird little balls customers find in their lawns. Our recent Quick Tips on out of the ordinary subjects, like dog vomit fungus, have been so popular I figured it was time to tackle this as my next Quick Tip subject.

These little ‘balls’ are galls, which are plant tissue growths caused by exposure to minute amounts of hormone-like chemicals produced by the gall makers. The gall makers can be fungi, bacteria, nematodes, or mites, but usually it is insects that cause them. Galls can actually occur on roots, flowers, bark and buds, but people generally notice them when they are on leaves or twigs.

Most of the questions I get are regarding galls that appear on our customer’s oak trees. On live oak trees, which many of our customers have, it is usually mealy oak galls. These little tan balls are about the size of a jaw breaker. They will eventually drop, at which point they are woody and hard under bare feet. If you look closely at one you’ll note a single exit hole where the adult gall maker gnawed its way out of its home.

With mealy oak galls the gall maker is a wasp, but keep in mind that Entomologists call it a wasp (most people associate wasps as an insect that can sting.) In this case the wasp that has produced the gall isn’t the stinging type.

The way it works is that a mother wasp find a good live oak twig where she can attach her egg, and the chemicals on the egg induce the oak to grow a home for the soon-to-hatch grub. That is how these mealy oak galls form. The grub feeds on the interior until it is mature enough to chew its way through the outer shell into the world.
Mother wasp finds an appropriate live oak twig to which she attaches her egg, and the chemicals on the egg induce the oak to grow a home for the soon-to-hatch grub. That is how Mealy Oak Galls are formed. The grub dines on the interior tissue of the gall until it matures and chews its way through the outer shell. Once vacant the gall shell can persist on the twig for a long time until it eventually drops into your lawn.

For most galls on oak trees, the insect is a species of cynipid wasp. And, strangely enough, each species of wasp is associated with a specific species of oak tree.

While some galls can be harmful, it is important to note that oak goals are not. They don’t do much to harm you tree. And applying insecticides to manage any perceived problem is overkill in my professional opinion. If you are worried about how they look, take comfort that gall makers tend run in cycles. Some years will be heavy and others will be minimal

If you have a question regarding your lawn and landscape give us call at 972.495.6990 or email me at [email protected].