Insects that might bug us this summer

The Emerald Ash Borer (Agrilus planipennis) is a very destructive pest that attacks any species of ash tree (green, black, or white ash). Saplings to very large trees can be infested, even healthy ones. Within three years, the tree probably will die as the larvae tunnel under the tree’s bark. The tiny adult is only one third to one half inch long and is a bright metallic green in color. This insect, native to China and Korea, was first discovered in North America in the Detroit/Windsor areas in June, 2002. The Emerald Ash Borer has moved as far west as northern Illinois counties, so the borers are on their way here. Already more than 20 million ash trees have been killed. There are 870 million ash trees at risk in our Minnesota forests and urban plantings. Because some infestations have been tracked to the transport of firewood, don’t transport it. Always buy or collect your firewood in the area where you will use it. Observe your ash trees for dieback in the top of the tree, abnormal sprouts on the base and sides of the trunk and branches, tiny D-shaped exit holes in the bark, and crisscrossing tunnels under the bark caused by the larvae. If you suspect Emerald Ash Borer infestation, contact the Minnesota Department of Agriculture on their Arrest the Pests Hotline at (651) 201-MOTH (6684) or 1-888-545-MOTH (6684).

The Japanese Beetle (Popillia japonica) is about 3/8 of an inch long. Its front end is a dark metallic green; the wings are a metallic dark tan. Look for two small white hair patches at its rear end and 5 white hair patches along each side. They often feed in bunches and will eat until only the veins of the skeletonized leaves remain. The adult chews on over 300 species of plant leaves, and the larvae feed on the roots of turfgrass. Adults love the leaves of grapes, roses, apple, elm, linden, birch and raspberry. Stillwater residents saw many beetles last year. Beetle traps have been shown to attract 4 times as many beetles to the area than locations without traps (convince your neighbors to put up beetle traps and your yard should be relatively beetle free). Milky spore disease had been used in the past to control the grubs, but in recent years the manufactured product has become less virulent and less effective. Hand picking and drowning the beetles in soapy water may control a small outbreak of the beetle. Check the University of MN article, “Japanese Beetle Management in Minnesota” (http://www.extension.umn.edu/distribution/horticulture/DG7664.html) for the latest chemical control methods for adults and grubs.

The Two-lined Chestnut Borer (Agrilus bilineatus) is a relative of the Emerald Ash Borer and is in Minnesota. Hundreds of oak trees are killed by this insect in Minnesota each year. It attacks all species of oak trees, especially red oaks. The insect is small (1/4 to ½ inch long) with two whitish or yellow stripes down its back. The larvae tunnel under the bark and destroy the water/nutrient transport vessels, girdling the tree. Oak trees that have been weakened by drought stress, construction damage (soil compaction, changes in soil grade, changes in water drainage), bark or limb damage, are susceptible to attack. Healthy trees are affected only minimally by limb damage. Infested trees will start dying from the top down and will look like they are drought stressed. Exit holes of the insect are D-shaped. The condition may be confused with oak wilt disease. It may take up to 3 years for the tree to die. Avoid this pest by caring for your oak trees. Mulch around the trees to prevent lawn mower damage and to preserve moisture. It is very important to water your trees slowly during dry periods to prevent drought stress. When building, avoid driving construction equipment near your trees to prevent compaction. Avoid cutting the roots, or smothering them with added soil. Your oak trees are a valuable landscape asset. Don’t attract the Two-lined Chestnut Borer.

Happy Gardening, Joe Baltrukonis

Information for this article was obtained from Dr. Phil Pelliteri, University of Wisconsin Department of Entomology (“Bugs of 2007”, Wisconsin Public Television Garden Expo, February 10, 2008) and from the University of Minnesota Extension website (http://www.extension.umn.edu/gardeninfo/).