Invasive Insect Contributing to Red Pine Die-off on Mount Desert Island

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Date: September 16, 2014
Contact: Judy Hazen-Connery, 207-288-8721
Contact: Alison Kanoti, 207-287-2431

An invasive exotic insect, red pine scale, has been confirmed by Maine Department of Agriculture, Conservation and Forestry Forest Service entomologists on dying red pines on the south side of Norumbega Mountain, near Lower Hadlock Pond, in the town of Mount Desert. Red pine scale was discovered in the US in 1946 in Connecticut, and since then has severely affected red pine stands in Connecticut, Rhode Island, New York, Pennsylvania, and more recently, New Hampshire. This is the first confirmed infestation of red pine scale in Maine.


Red pine scale is also known to affect several horticultural pines, such as Japanese red pine, Japanese black pine and Chinese pine. It is not known to affect jack, pitch, Scotch, white, Austrian and mugho pines.

Red pine trees across Maine are under stress from multiple agents. Regular inspections of dying trees on Mount Desert Island by Maine Forest Service staff previously determined that two shoot blights have been contributing to mortality of red pine here for at least five years, especially in areas of thin soils and southern exposures. High levels of mortality from these fungal diseases may have delayed recognition of the tiny scale insects, which are about the size of the head of a pin.

This time of year, some life stages look like tiny elliptical shells, and others spin small, white, woolly tufts where they settle on the twigs.

National Park Service (NPS) biologists are working with the Maine Forest Service and US Forest Service entomologists and other conservation partners on response planning, including gathering more information about the extent of the infestation. The NPS announced that Mount Desert Island will be included in a new study of red pine decline across New England that will be conducted by researchers from the University of New Hampshire and the US Forest Service. Park managers hope that lessons learned from this infestation will be used to slow further spread of red pine scale and protect forests from similar pests such as hemlock woolly adelgid.

Acadia National Park Deputy Superintendent, David Manski, said that surveys to delineate affected areas will be conducted by trained entomologists this winter, when there is less risk of spreading the pest to unaffected areas. Eggs, immature scales called “crawlers” and adult scales, all present now, can be carried on clothing and vehicles, as well as by birds, mammals and strong winds. Park staff will also survey NPS forests adjacent to Sargeant Drive to identify and remove any dead trees that pose a hazard to motorists. “We anticipate that few of these trees will pose an immediate threat because red pine trees that have recently died are slow to decay and generally not susceptible to windthrow,” Mr. Manski added.

Park managers currently have no plans to cut and remove dead or dying red pines on large areas. Although salvage harvests have occurred in other states where red pine scale has killed trees, harvests do not appear to have prevented the spread of the insect. In fact, moving trimmed or harvested materials in spring through fall can actually spread the insect. Maine Forest Service Entomologist, Allison Kanoti, who confirmed the identification of the red pine scale last week on materials submitted by a local gardener, advised that little research on other forms of control has been conducted recently.

NPS Fire Ecologist, Melissa Forder, inspected one affected area on Norumbega Mountain in late August to determine if dying red pine trees presented an increased threat of wildfire. She found that while there was a temporary increase in fine fuels caused by falling needles and twigs, the increase in fuels wouldn’t pose an immediate danger. She stated that wildfire potential would need to be assessed as the extent and severity of the infestation was determined.

Park biologists note that trees in the understory will likely respond to increased light conditions with quick and vigorous growth. As dead red pines trees begin to be recycled, they may provide important habitat to bats, woodpeckers, and other cavity dwellers, and will return nutrients to the soil for the next forest that will replace the dying overstory.

As with trees affected with shoot blights, branches on scale-impacted red pine tend to die from the bottom up. However, with scale damage, needles turn orange towards the inside of the tree first, with newer needles towards the tips changing color last. Please report areas suspected to have damage from this pest to the Maine Department of Agriculture, Conservation and Forestry, Maine Forest Service’s Insect and Disease Laboratory staff in Augusta at 207-287-2431 or email forestinfo@maine.gov.

For further information on red pine scale see: www.maine.gov/forestpests#rps



Last updated: February 26, 2015

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