Hemlock sawfly defoliation, Chaik Bay, Admiralty Island 2018. (Photo Credit USFS.) Juneau, Alaska (KINY) - The United States Forest Service released an Alaska Forest Health Highlights report for 2020 and says the Hemlock sawfly outbreak that began in 2018 and peaked in 2019 has decreased in activity throughout Southeast Alaska.
Immature Hemlock sawfly larvae feed only on old foliage, but mature larvae will also attack new foliage if all of the older foliage is depleted.
High populations of the sawfly may remove all of the older foliage.
This makes the tree crowns appear thin and gray.
If defoliation occurs for two or more successive years, trees are weakened and may die or succumb later to diseases or other insects.