Property owners encouraged to inspect hemlock trees for infestation

December 22, 2023

Property owners encouraged to inspect hemlock trees for infestation

If you see tiny balls of a white, woolly material lining your hemlock branches this winter, contact the Mason-Lake Conservation District (MLCD). These could indicate the presence of a tiny invasive insect, hemlock woolly adelgid (HWA). HWA has been moving north along Lake Michigan since 2016 and is now present in Allegan, Ottawa, Muskegon, Oceana, Mason, Benzie, and Washtenaw counties. HWA poses a significant threat to eastern hemlock trees in Michigan – an infestation can kill a large, otherwise healthy tree in less than a decade. Properties within five miles of the lakeshore and along river corridors are most at risk. Currently, the furthest north infestation is just north of Nordhouse Dunes in Grant Township, although the majority of infestations are still south of Hamlin Lake.

MLCD conducts free, early detection surveys for private property owners each winter on thousands of acres of land in its service area to detect early infestations before they become severe. This survey effort entails checking the undersides of hemlock branches for the tell-tale white ovisacs in which HWA lays its eggs. During the spring and summer months, 100s of eggs will hatch from each ovisac into  “crawlers”, which are mobile larvae that can spread between trees via wind, birds, squirrels, vehicles, forestry equipment, nursery stock, and even clothing.

HWA feeds by attaching itself to the undersides of hemlock branches, between the base of the needle and the stem, and sucks the sap out of the tree. The tree responds to this stress by cutting off sap circulation to those branches, weakening and eventually killing the tree in four to 10 years if the infestation is not remedied. Because infestations spread rapidly, HWA can quickly overtake hemlock-dominated forests. Along the East Coast where HWA has been present for 50 years, HWA has devastated hemlock populations.

If HWA is detected on your property, free opt-in chemical treatment is available contingent on grant funding and state priority guidance. A delimitation survey is conducted in which every hemlock tree within an 800 foot buffer of an infestation is measured and tagged. Once this is completed, each tree is treated during the late spring and summer months with an insecticide to contain and eliminate the infestation. These treatments are typically effective for four to seven years and  prevent infestations during that time.

Outside of Mason County, many other organizations are doing similar work to protect hemlocks all over Michigan, typically with extensive collaboration to help distribute the efforts required for such a large undertaking to be realized. Mason-Lake Conservation District HWA efforts are made possible through funding from the Michigan Invasive Species Grant Program.

Contact Bri Jasinski at the Mason-Lake Conservation District at 231-757-3707, ext. 111 or bri.jasinski@macd.org.

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