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Forest Pests
Article #143, April 2009
By Bill Cook

     Spring has finally arrived! Soon the air will be filled with seasonal scents, pollen, insects, and fungal spores. For the forests, it's the time to grow and reproduce. And, of course, there will be plenty of pests that feed on trees.

     The emerald ash borer (EAB) has three known colonies in the Upper Peninsula, in Chippewa, Delta, and Houghton Counties. Each of these outbreaks has been around for years, although they have only been recently discovered. Researchers and technicians will be learning more about these sites, as well as be looking for additional infestations. We will likely hear more about EAB this growing season.

     Beech bark disease (BBD) will continue to spread throughout the eastern range of beech. BBD has already caused widespread damage in the U.P., as well as in other regions of the country. The U.P. beech was the last large North American stronghold. BBD is a curious partnership between an insect called a "scale" and several species of Nectria fungus. The scale is an aphid-like creature that allows the fungal species to invade the tree and kill it. Beech and oaks are among the few "mast", or hard seed, producing species in the north, which makes these tree species particularly important for many species of wildlife.

     Oak wilt is another fungus that slowly works its way through oak forests, killing nearly every tree in a stand. As far as we know, the only U.P. outbreaks are in Menominee and Dickinson Counties, with a particularly high concentration in the Shakey Lakes area of Menominee County. Oak wilt colonizes new areas via spores that hitch-hike on insects and, possibly, other mobile creatures that feed on or cause wounds in healthy oak trees. Once established, the deadly disease spreads through the inter-connected root systems of oaks, an especially common growth pattern among trees in the red oak group of species. To minimize risk of this disease, avoid wounding oaks from early May through the end of July.

     The last three droughty growing seasons have weakened many trees in our forests. A weakened or stressed tree becomes more vulnerable to a wide range of pests. Dead and dying patches of tamarack are common examples. Often tree death has more to do with unseen drought stress than the secondary infestation of a particular insect or disease. Trees along highways and in residential areas are especially vulnerable due to their already environmentally challenging habitat. Wood and bark boring insects and soil-resident pathogens commonly take advantage of stressed trees.

     Gypsy moth larvae appear as leaves begin to unfurl. They particularly like to eat oak leaves. During favorable spring weather, populations can mushroom and cause extensive defoliation and, sometimes, tree death. Warm, dry springs favor gypsy moth. Cool, moist springs favor the Entomophaga fungus which kills gypsy moth larvae.

     Jack pine budworm will likely cause extensive damage in some jack pine forests, especially the mature stands that are less vigorous. Well-managed stands are more resistant. By mid-summer, affected stands begin to show characteristic reddish crowns from dead needles. There are many other species of budworms whose populations boom and bust over the years. Red pine, white spruce, and balsam fir are common host targets. Conifer stands with high mortality result in much higher risk for wildfire.

     The list of other pests is long, including some headline species such as the Asian long-horned beetle, hemlock woolly adelgid, Sirex wood wasp, forest tent caterpillar, maple decline, white pine blister rust, and many others. The best way to maintain a healthy forest is through proper management. Pest impacts can often be minimized or avoided. Interested in improving forest health? Contact a forester.

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Bill Cook is an MSU Extension forester providing educational programming for the entire Upper Peninsula. His office is located at the MSU Upper Peninsula Tree Improvement Center near Escanaba. The Center is the headquarters for three MSU Forestry properties in the U.P., with a combined area of about 8,000 acres. He can be reached at cookwi@msu.edu or 906-786-1575.

Prepared by Bill Cook, Forester/Biologist, Michigan State University Extension, 6005 J Road, Escanaba, MI  49829
906-786-1575 (voice),  906-786-9370 (fax),  e-mail:  cookwi@msu.edu

Use / reprinting of these articles is encouraged. Please notify Bill Cook.
By-line should read "Bill Cook, MSU Extension" Please use the article trailer whenever possible.

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