Forest pests

Learn about pests that affect forests.

Midsummer is upon us and we’re now on the backside of the growing season. Much of the region has experienced drought, although local water conditions are highly variable. Forests have been affected and so have forest pests.

Spruce budworm flare-ups occurred sporadically across parts of the western Upper Peninsula and, perhaps, a few other areas. The feeding was done by mid-June and some forest stands currently appear terrible. However, after the browned needles drop by the fall, the firs and spruces should look better. Next spring, buds often refoliate trees that have not been severely damaged or suffer from other health issues.

Fall webworm nests have become abundant on a wide variety of hardwood species. They are sometimes mistaken for tent caterpillars, which occur in the spring. The webworms skeletonize leaves, which then turn brown. The ugly nest caterpillar may also turn-up in loose web nests. Webworms are hairy. Ugly nest caterpillars are hairless, yellow, and have dark heads.

Tamaracks continue to die from a combination of drought, larch casebearer, and bark beetles. Older tamaracks are more vulnerable. This scenario has been ongoing for several years. In most cases, smaller tamaracks are present and will grow to replace the dead trees.

Beech bark disease (BBD) has ravaged most of the once substantial Michigan beech resource. BBD has been in North America since the late 1800s and killed most of the eastern beech. Michigan had the last remaining large stands of beech. BBD is a combination of an exotic scale insect, exotic fungus and native fungus.

Oak wilt has become widespread throughout much of the Michigan oak resource. This exotic fungus spreads both overland through insect vectors and underground through root grafts. Trees in the red oak taxonomic group are most vulnerable. Avoid pruning or damaging oaks from Memorial Day through Labor Day to reduce the risk of infection.

Wilting oaks can also be caused by two-lined chestnut borers (TLCB). Populations increase on drought-stricken, older oaks, trees on poor soils, and on other tree species. TLCB is easily evidenced by tunnels under the bark. Firewood cutters are familiar with these tunnels.

The emerald ash borer (EAB) is a cousin of the TLCB but hails from China and has been killing all species of ash in North America for more than a decade. EAB was first identified in 2002 in Detroit and is widespread throughout many eastern states. There are several affected areas in the Upper Peninsula.

Large areas of sugar maple forests have been declining, especially in the western Upper Peninsula. The cause(s) for this decline are unknown but are being researched by Michigan Technological University. The decline appears to be getting worse.

There are a few familiar standbys which remain active in our forests. White pine blister rust, Dutch elm disease, Hypoxylon on aspen, black knot on cherry, deer overbrowsing, and a large host of borers, miners, sawflies, anthracnoses, rusts, galls, scorches, winter injuries and other ailments. The forest is a cornucopia of organisms that feed on trees, most of which are natural, normal and usually harmless to tree health.

Other pests of note, either waning, building or on the horizon, include forest tent caterpillar, Asian long-horned beetle, hemlock woolly adelgid, thousand cankers disease, Annosum root disease, declines of hickory and butternut, and gypsy moth. Gypsy moth may have some localized flare-ups due to the dry spring which favors the insect.

Pests can also include a number of invasive plants that have been degrading forest systems for years, including buckthorn, garlic mustard, leafy spurge and Pennsylvania sedge. These species reduce regeneration of trees and other forest plants, and alter ecological dynamics.

The Michigan Department of Natural Resources (DNR) publishes an annual forest health report, which is a good reference of highlights for any given year.

The best defense against pests and other forest stressors is to maintain a healthy and vigorous forest through good forest management. Management yields a range of other benefits as well, from revenue to ecological services. Michigan has a competent force of forestry consultants available to assist forest owners as they maintain and enhance their forest resources. Healthy forests are often a choice.

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