Carrie Barre-LiBaire's Gardening Column

Down to Earth Gardening

Are there Mexican jumping beans in Minnesota? No, but some residents of our area are experiencing a similar phenomenon called Jumping Oak Gall. Little white rice-like bodies are falling from their oak trees and then start jumping around. This is usually followed by a call to the Douglas County Extension Office, either in panic or laughter. The jumping oak gall is nothing more than an active tiny wasp larva inside the gall.

Galls are abnormal plant growth that can be found on the leaf, twig or bud of plants. The most common galls appear on the leaves of trees as small bumps, and are usually thought to be the eggs of an insect. This can be the case, but galls can also be caused by many different organisms, including mites, fungi and bacteria. The gall itself is the result of the plant's reaction to the organism. The organisms do not make the gall, the plant does. The activity of the organism (biting, sucking, laying eggs) causes the plant to increase production of normal plant growth hormones, which then result in the formation of a gall. Though somewhat alarming to find, galls are not harmful, outside control is not recommended.

The types of galls we are finding right now occur on Oak, Maple, Hackberry, and Ash trees. We are seeing many cases of Maple Bladder Gall this year. These are easy to identify because they are small red galls found on the top of the maple leaves. They are caused by Eriophyid Mites. Each gall contains many of these mites, and there is an opening on the underside of the gall, which enables the mites to crawl out of the opening and infect new leaves. Their activity will cease in July and the mites will migrate to the tree bark to spend the winter.

Hackberry nipple gall is also very common this year. Just like the name implies, cylindrical formations hang down from the leaf of the Hackberry. These are caused by Psyllids, or Jumping Plant Lice. Psyllids are small insects related to aphids. The galls form from them feeding on the leaves. Psyllids can become quite a nuisance in the fall when they enter your home through the window screens in an attempt to seek winter shelter.

On Ash, the ash flower gall is common. You will notice brown, dried up clusters on your tree. These galls are caused by tiny mites that enter the flower of the male ash tree in April. The mites then puncture the flower bud, injecting a growth promoting substance in it. The flowers then form abnormal clusters of galls.

I usually don't find the lives of insects interesting, but seeing these cases the last few weeks has really peaked my interest. I find the relationship between these insects and their host plant fascinating. Some basic knowledge of the insects around our garden can either arm us with an insecticide, or make us realize that the scary looking thing on our plant is harmless, and you can let it be.

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