TWIN LAKE — Hemlock woolly adelgid (HWA) continues to plague trees in West Michigan, with the Northwest Michigan Invasive Species Network estimating that 170 million trees in the state are at risk of dying as a result of the invasive parasite. The Muskegon Conservation District is among the organizations trying to fight back.
MCD forest pest manager Lance McCarty did a presentation and a demonstration on protecting hemlock trees from HWA Wednesday evening at the Dalton Township library. About a dozen landowners turned out to receive pointers on fighting HWA.
MCD, based in Twin Lake, offers its services to those who suspect HWA is on their property or want to fight it. The organization offers free site visits and, as a nonprofit, says it does not charge for anything that isn't necessary to complete a job, which includes surveying and, if necessary, treating hemlock trees.
According to several sources, HWA first made it to the United States by accident from Japan in the 1950s when plants imported from the country brought it over. It was first observed on the East Coast of the U.S. at that time and has slowly propagated since. It's been known to be in Michigan for about 10 years. The parasite, which manifests as white woolly sacs on the branches of trees, takes nutrients the trees need to survive and slowly kills them as a result. If untreated, trees often die within 4-10 years of being exposed to HWA.
This invasive species is an even more urgent issue than some others, McCarty said, because of the importance of hemlock trees to ecosystems.
"It's a keystone species," McCarty said, meaning that other species gain benefits specifically from hemlocks. "There's really no replacement for them."
While the MCD is a recommended method for treating afflicted trees, landowners can do so themselves, but the MCD recommends care be taken. The chemicals needed to treat HWA are dangerous, and it's imperative safety steps are taken, including the covering of all possible skin when doing the treatments. In addition, to avoid the chemicals seeping into groundwater, the MCD recommends until at least 12 and ideally 24 hours of dryness surround the treatments, that wind speeds are under 10 miles per hour at the time, and that treatments do not take place within 50 feet of a well if the property has well water.
One of two chemicals, McCarty said, are usually used to treat HWA. One, imidacloprid, is a longer-lasting treatment, protecting trees for 5-7 years. However, the downside is that it takes 12-18 months for it to take effect. For trees in more imminent danger, dinotefuran is a quicker fix, taking effect within a month; however, that treatment only provides about a year of protection. It is possible to use both chemicals, though the MCD recommends at least two weeks lead time in between.
McCarty said to determine how much of the chemical to spray on hemlock trees, measure the circumference of the tree in question and divide by pi (3.14) to get the diameter. For each diameter inch, 1.5 fluid ounces of chemical should be sprayed onto a tree. (Injection treatments are also possible, but due to the required equipment probably would not be done by a landowner.)
Alternatively, landowners who detect HWA could log their trees, as McCarty told one attendee who asked about it. However, due to Michigan quarantine rules surrounding HWA, again care should be taken; he said any logging company a landowner would work with should be made aware of the issue beforehand so they can take appropriate precautions.
Anyone with questions is welcome to contact MCD at its Twin Lake location or by email at muskegoncd@macd.org.
