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Showing posts from May, 2010

Eastern Tent Caterpillars

Jeffrey Hahn, Asst. Extension Entomologist

Eastern tent caterpillars have been common in many areas of Minnesota this spring. This insect is easy to identify because it constructs a silken web in the fork of branches. They attack a variety of hardwood trees, especially fruit trees, including apple, crab apple, chokecherry, cherry. These caterpillars are bluish black with yellow and a white stripe running the length of the top of its body. They are also mostly smooth except for a series of hairs sticking out along the side of their bodies. They are two inches when fully grown.
Eastern tent caterpillars normally emerge late April to early May. This year they emerged several weeks early because of the unseasonably warm weather we experienced in March and April. As a result, most, if not all of the caterpillars are fully grown and finished feeding.

The best time to treat eastern tent caterpillars is when they are half full grown length or less, i.e. no more than one inch long. An …

New Emerald Ash Borer (EAB) Fact Sheet Available

Jeffrey Hahn, Asst. Extension Entomologist

A publication entitled A Guide for Homeowners on Pesticide Selection, Use, Safety, and Environmental Protection is now available. This fact sheet was written by the Minnesota Dept. of Agriculture with help from the University of Minnesota Extension and Dept. of Natural Resources. It discusses factors to consider before using an insecticide, insecticide treatment options, recommendations to protect water quality, information on insecticide labels, and how to measure trees.
A clarification should be made regarding the timing of insecticides. The included chart is generally true but it should be noted that imidacloprid should be treated in spring about 4 - 6 weeks before EAB is expected to emerge, i.e. late May or early June or the previous fall. We are at the end of the time for treatment with imidacloprid. However, the use of Tree age (emamectin benzoate) can still be used until late May to early June.

You can find this publication at the…

Crown Gall: A bacteria at the root of the problem

Michelle Grabowski, UMN Extension Educator

As you purchase new plants for your garden or landscape this spring, one plant disease to look out for is crown gall. Crown gall is caused by the bacteria Agrobacterium tumefaciens. As its name implies, the crown bacteria causes a tumor like growth on the stems and roots of infected plants. Galls are round, rough textured growths. New galls are often light colored and may be smooth and slightly spongy. Older galls become hard and dry; often dark in color with many rough cracks and fissures. The most common place for galls to form is on the main stem, at the point where it enters the soil. Galls can also form on below ground roots. In some plant species, the bacteria travel through the plants vascular system and initiates rows of galls along branches.
The presence of galls on roots or the main stem of a plant may or may not affect the overall growth and productivity of the plant. Young plants with many galls and plants with a gall completely e…