More Trouble for Trees: Sap-sucking pest finds way to Michigan

Another potentially devastating Asian insect has turned up on Michigan's trees.

This time, the target is hemlocks, which are popular landscape evergreens. The native eastern hemlock is also an important component of hardwood forests in northern Michigan.

"It's potentially quite serious, but it's really localized," said Ron Murray of the Michigan Department of Natural Resources.

A landscaper recently alerted the Michigan Department of Agriculture about white, cottony masses on hemlocks that had been planted in 2003 at four sites in Harbor Springs. The trees came from the same nursery in West Virginia, a state where the hemlock woolly adelgid (ah-DELL-jhid) is already known.

The state agriculture department confirmed a patchy adelgid infestation of some of the 30 landscape hemlocks and on several large native hemlocks nearby.

The hemlock woolly adelgid is among the most serious exotic forest insect pests to have entered Michigan, said Deborah McCullough, a forest entomologist at Michigan State University.

Experts from the state agriculture and natural resources departments and from Michigan State University are working on a plan to eradicate the sap-sucking insect, which may include destroying infested trees and applying insecticide to others.

Agriculture officials are also trying to track where 1,900 hemlocks imported to northwest northern Michigan from out-of-state growers ended up and whether the trees are healthy. Surveys will occur this fall, when the cottony masses are most evident.

The state agriculture department has been on the lookout for hemlock woolly adelgid for two decades and has already been inspecting nursery stock. Twice before, trees infested with the adelgid have been found and destroyed.

But this is the first time it has been discovered on Michigan's native hemlock trees. The insect is transported by wind, people and animals.

Experts hope that, compared with the emerald ash borer -- which has killed more than 16 million Michigan ash trees and also originated in Asia -- the hemlock woolly adelgid will be easier to contain. For one thing, it is easy to see, and there are also already-tested insecticides, since it has been a problem for decades on the East Coast.

The insect damage can cause the normally deep-green tree to look gray, and white cottony masses make the ornamental tree less attractive. After several seasons, it can also kill the tree.

Treatments should be used only after a hemlock is infested. Some beetles are being investigated as a long-term biological control.

Nationwide, about half of all native eastern hemlocks are infested with the adelgid, according to Bradley Onken, an entomologist on a U.S. Department of Agriculture Forest Service task force studying the insect.

Onken said there is no estimate of the economic impact, although many hemlocks grow in high-visibility areas such as parks and campgrounds.

Cold winter temperatures may suppress the hemlock woolly adelgid population in the northern Lower and Upper peninsulas, where native Michigan hemlocks are most prevalent, McCullough said.

"If a lot die over the winter, that would be a great thing," she said.

Murray said the number of native hemlocks in Michigan is unknown, but there are fewer of them than of many other trees, including maples, pines, oaks and ashes.

As landscape evergreens, hemlocks are not as widely planted as pines and spruces but are often used in partly shaded spots as specimens or hedges. A 6-foot-tall hemlock retails for about $200, according to a spokesman for Ray Wiegand's Nursery in Lenox Township.