By Bev Johnson

Master Gardener

Bunkey noticed some odd lumps on the leaves on one of his Burr oaks. Since it shaded the house from the hot summer sun he didn’t want to lose it. He picked a few of the leaves and took them to the Extension office. There he was told that the lumps were galls and didn’t hurt the tree at all. The leaves just look ugly. “What causes this?” he asked. This is what he found out.

Galls are abnormal plant growths caused by insect and mite-induced growths. The result is from the interaction of insects or mites. They are usually formed in the spring when leaves are first developing. When the insects or mites lay eggs or feed on the leaves the leaves are stimulated to produce a proliferation of cells at the site of the attack. Galls come in many colors, shapes and sizes. Each species of gall maker produces a unique gall. It is important to recognize galls as they can be confused with disease or other tree problems.

One of the more common galls is the spindle gall, also called a finger gall. They are produced by tiny eriophyid mites. The galls they make appear as slender projections on the upper surface of the leaf, standing up to ½ inch tall. They can be red or green. They are common on plums, maple, cherry, elm and linden leaves.

Another common type of gall is erineum or velvet gall. These are carpet-like growths found on the upper surface of leaves. They are often bright red but also come in a cream color. They are particularly noticed on birch trees but can hit maple, viburnum and lindens. They can also be caused by eriophyid mites.

A similar gall was discovered on a butternut tree. It is also a type of eriophyid mites and forms a mass of short hair-like structures. These aren’t red but dark brown, somewhat puckered galls on the top of the leaf. Underneath it is whitish.

Oaks are blessed with the highest number of different kinds of galls found on them. A particularly striking gall is the hedgehog gall found on bur and white oaks. This gall is oval, spiny and can grow up to 1/2 inch long. Its bright yellow, orange or red. It’s common to find them on major leaf veins. These galls are produced by small cynipid wasps, a group of gall making wasps.

Interesting or ugly as they may look, leaf galls aren’t dangerous to trees and have essentially no impact on tree health. No treatment is needed, just ignore them. Or, if you have bored kids, send them out to find as many different galls as they can and help them figure out which insect made which gall. Those lumps in goldenrod stems are also caused by galls. The worm inside makes good fish bait.

Now that we are in the summer furnace weather, there are a few don’ts. One don’t is –don’t apply broadleaf herbicides if the temps are over 85 degrees. It drifts. Don’t do any lawn renovations until September. Do keep deadheading flowers to keep them blooming. Blooms are mostly water. Don’t forget that trees and shrubs need watering too. Every growing plant needs an inch of water a week.  Don’t fertilize trees, shrubs, or roses now. They are already preparing for winter and don’t need a flush of growth this time of year.

Now is the time for the gardener to turn up the A.C, grab a lemonade and a good book and just vegetate. Fall clean up isn’t that far off.