Population of elongate hemlock scale found for the first time in a natural setting of hemlocks in southern Maine raises threat to state's forest health, say Maine Forest Service officials
November 10, 2010
– A new population of an invasive insect that damages hemlocks has been discovered in southern Maine, according to Maine Forest Service officials.
A population of elongate hemlock scale was found for the first time in a natural setting of hemlocks, rather than an ornamental landscape setting, on Tuesday in Kittery Point, Maine Forest Service (MFS) entomologists announced this week.
The presence of elongate hemlock scale in a natural forest setting means that there is an additional threat to Maine’s forest health, they warn.
The scale also can exist in fir trees. Though it hasn’t yet been discovered in Maine in natural fir stands, its presence and possible need for treatment could eventually impact the state’s commercial Christmas tree industry, the state officials predict.
The discovery this week of elongate hemlock scale also follows recent findings that an associated invasive species that destroys hemlocks – hemlock woolly adelgid (HWA) – has spread farther up the coast of Maine from South Portland to Bristol, the MFS entomologists said.
“This is a pest we have not had before in Maine,” Dave Struble, MFS state entomologist, said about elongate hemlock scale. “Like hemlock woolly adelgid, it is an exotic, and it has infiltrated into Maine from the south.
“Either one is bad enough,” the state entomologist continued, “but scale and adelgid together is a recipe to accelerate tree decline and mortality.”
Hemlocks are a significant Maine tree species, usually found near water bodies, which contribute to the state’s forest ecosystem. They protect the forest floor from erosion and help water quality particularly by buffering water temperatures, which can affect such species as brook trout. Hemlocks also help deer wintering areas.
Elongate hemlock scale is an Asian insect that looks like brown and white scales on the underside of hemlock needles. In areas where it has been established, it is often associated with HWA. It causes needles to yellow and drop. It had been found previously in Kennebunkport and Kennebunk on landscape hemlock, where it has been controlled with spraying.
HWA is an invasive species from Asia that kills eastern and Carolina hemlock. It has been found in at least 16 states and was first discovered in Kittery in 2003. Since then, it has been spreading up the coastal area of Maine.
HWA is distinguished by white, woolly masses found at the base of needles on the undersides of hemlock twigs. Infested trees also have off-color needles, often with a grayish cast, and premature needle drop and twig dieback.
Allison Kanoti, MFS entomologist, said the scale was discovered this week while MFS staff were monitoring the establishment of colonies of two predatory beetles that eat and control HWA and moving them to new locations.
Using a new basket method of collection, the MFS staff gathered mid-canopy samples from natural hemlocks and found the elongate hemlock scale, Kanoti said.
“Every tree we sampled at the site had scale,” the MFS entomologist said. “It wasn’t as noticeable from down below. We probably wouldn’t have seen it if we hadn’t been sampling upper branches. Clearly it has been here for a while.”
The area already has been infested with HWA since 2003, Kanoti said. The scale is “an additional threat and was expected eventually,” she said, “and just another factor in causing forest decline.”
In addition, the HWA population in recent months has continued spread up the coast from the Harpswell/Phippsburg area and has been found in South Portland on Great Diamond Island and areas north to Bristol, Kanoti said.
Scale infestation also has been found in the New Hampshire seacoast area, and entomologists in Connecticut and Massachusetts are reporting more problems in those states with scale than with HWA, Kanoti noted.
Scale and adelgid in natural forest settings are spread by wind, birds and mammals, and both are very difficult to stop. “Their natural spread is just not something for which we have tools to control,” Kanoti said.
The Maine Forest Service, however, has been working extensively to introduce and cultivate predator beetles to control HWA. Some work also has been done at the University of Vermont on using fungal diseases to control both invasive species, Kanoti said.
“A lot of forest managers think these fungal diseases have a lot of promise for the future as tools for control,” the entomologist said.
Kanoti warned coastal-area residents, even those living as far up the coast into Washington County, to continue to look for signs of both invasive species. Residents are asked to take needle samples and to report their findings to the Maine Forest Service Entomology Laboratory.