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Small insect causing huge problems for Michigan's hemlock trees

The bugs are threatening to decimate part of the state's 170 million hemlocks
Posted at 6:50 PM, Jan 14, 2022
and last updated 2022-01-14 18:58:48-05

NORTON SHORES, Mich. — A small insect could create a huge problem for one of Michigan’s most prominent tree species.

Hemlock Wooly Adelgids, or HWAs, are tiny insects that nest at the base of hemlock trees and can kill a full-sized tree in as little as four years.

“We have roughly 170 million hemlocks here in the state, and this has the potential to have a lot of impact and kill a lot of trees,” said Drew Rayner, the HWA coordinator for the state's Department of Natural Resources. “This would be a big loss to lose our Hemlock tress, as well as the wildlife value.”

Hemlocks, which grow mainly in dune and cold-water-stream ecosystems in Michigan, provide habitats to animals. They’re also present in many people’s yards as ornamental trees, and Rayner hopes people will keep an eye out for the easily identifiable nuisances, whose ulva sacks resemble white cotton balls on the underside of the hemlock branch.

“An HWA is always going to be lined up right at the base of the needle. It’s not going to be on the needle; it’s not going to be anywhere else,” said Rayner. “If left unaddressed, this will lead to the tree dying eventually.”

The HWAs were first discovered in Michigan by landscapers several years ago, and have already started doing their work in parts of West Michigan. Rayner says the HWAs have been found on hemlocks from Fennville to as far north as Ludington and typically appear within a mile inland of the Lake Michigan shoreline. The insects don’t impact any other tree species, but can be transferred via human contact, or from boats, trailers or recreational equipment. Their spread peaks in the spring and Rayner says they are relatively easy to treat with a simple insecticide, as long as DNR knows where to look.

“We can be really successful if it’s caught earlier; the sooner we treat the better,” he said. “We can save trees and we’re pretty effective at treating this.”

The east coast — namely Virginia — had a massive HWA outbreak in the 1950s that decimated their population of hemlock trees. Rayner says they’ve been in contact with agencies in that region to learn what they can.

The DNR wants you to report any sightings of Hemlock Wooly Adelgids. You can learn more about them or report a sighting to DNR here.

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