Aerial surveys conducted by the US Forest Service Forest Health Protection Office (FHP) and the Alaska Department of Natural Resources, Division of Forestry throughout forested regions of the state of Alaska this year mapped defoliation damage to birch, spruce, alder, willow and cottonwood across extensive areas of the state.
More than 200,000 acres of defoliation by birch leaf roller (Epinota solandriana) were mapped, with the most extensive damage between Anvikand Russian Mission on the Yukon River and from Crooked Creek to Tuluksak on theKuskokwim River. Severe damage was also seen around Lake Clark and Iliamna Lake.
Fewer acres of damage were mapped in locations scattered throughout interior, southwest and south-central Alaska; including the Kobuk River, upland from Bristol Bay, and the KenaiPeninsula. Birch leaf rollers were seen spilling over from their favored hosts (birches and alders) to willows, aspen, and cottonwoods.
A large area of damage on spruce (over 100,000 acres) caused by black-headed budworm (Aclerisgloverana) was found near the community of Aleknagik and Wood-Tikchik State Park.
More than 100,000 acres of alder defoliation or disease was noted. The most significant damage was seen along the west coast of Cook Inlet from McNeil River State Game Sanctuary north to ChinitnaBay and near Lake Clark Pass. Alder damage was also seen around the communities of Circle, Central, and Eagle northeast of Fairbanks and some defoliation has been seen on the Kenai Peninsula.
Reports of extensive alder defoliation have been coming in from Kodiak Island and from as far away as the community of Pilot Station on the Yukon-Kuskokwim Delta, but are not yet confirmed by FHPstaff. Birch leaf roller was found damaging alder on Lake Clark and might be causing alder damage elsewhere, along with Bruce spanworm (Operophtera bruceata), rusty tussock moth (Orygiaantiqua), and autumnal moth (Epirrita undulata). Large acreages of alder have also been damaged over the last few years by alder canker, a fungal disease.
All of the defoliation agents so far identified are native insects, although some defoliation in the Anchorage Bowl and Kenai Peninsula might be due to non-native green alder sawfly.
Defoliators tend to follow cycles of population growth over several years, often followed by a rapid decrease in numbers of insects and damage. Damage can appear quite severe but trees usually recover. Occasionally trees will die when attacked for several years in a row.
Current levels of defoliation have been building over the last few years. However, some species’ populations are increasing, some are at peak populations, and some are decreasing, but the amount of severe defoliation increased exponentially in 2013.
Native defoliating insects have natural enemies to keep their populations in check. Surveys of Southeast Alaska found low amounts of forest defoliation and mortality, with the exception of a continuing outbreak of hemlock sawfly damage on Revillagigedo Island.
More information on Forest Health in Alaska can be found at http://www.fs.usda.gov/goto/r10/fhp, or by contacting Jim Kruse, Entomologist, at (907) 451-2701 firstname.lastname@example.org or Tom Heutte, Aerial Survey Coordinator, at (907) 586-8835 email@example.com.
Photo caption / credit: Extensive area of blackheaded budworm on spruce, near Wood-Tickchik State Park. US Forest Service