An aphid-like insect called the Hemlock Woolly Adelgid (HWA) has invaded hemlock trees in at least 19 coastal Maine towns, including five in Lincoln County. The pest was first discovered in Maine in York County in 2003 and is slowly spreading up the Atlantic coastline. HWA has also been discovered in Sagadahoc and Cumberland counties.
The Maine Forestry Service has confirmed the presence of HWA in Bristol, South Bristol, Edegcomb, Wiscasset and Westport Island. The colony on Westport Island, discovered last week by a New Hampshire resident here on vacation, “is fairly well established,” Maine Forestry Entamologist Allison Kanoti said.
HWA was introduced from Japan to Virginia in the 1950s and has spread north along the eastern seaboard.
“We have only tested south of Rt. 1 in coastal towns. Hemlock woolly adelgid does well in that climate. It is warmer on the coast. On the coast the wind is always blowing which allows for more even distribution of them. We don’t have our arms around it yet.” Because of staffing, “there is only a limited area we can cover,” Kanoti added of the Forestry Service’s survey of coastal towns.
HWA is an aphid-like insect that covers itself with a white, waxy wool which acts as a protective coating. Adelgid infestations are easily recognizable by the appearance of tiny cotton balls at the base of the hemlock needles. The wool is most visible on the undersides of hemlock branches from fall through spring.
HWA feeds on the sap at the base of hemlock needles, disrupting nutrient flow and causing the needles to change from deep green to a grayish green. The needles then die and fall off. Without needles, the tree starves to death, usually within three to five years of the initial attack. Infestations usually start in large, mature hemlocks, but HWA also attacks younger trees.
The Maine Forestry service encourages landowners to check their hemlock trees, and report back to them if they find insect infestation on their trees. “If people would let us know it would be great. People need to take responsibility for their own hemlock,” Kanoti said.
Kanoti can be reached at 287-2431 or by email at Allison.M.Kanoti@maine.gov. Pictures of hemlock woolly adelgid can be seen online at www.forestryimages.org. Tips for identifying the HWA can be found at www.maine.gov/doc/mfs/HWAOverview.htm.
“Currently nothing can be done to stop it,” Kanoti said. HWA is spread by the wind, birds and small mammals. There are horticultural chemicals available if land owners have just one or two trees on their property, but “they are not going to work in a forest. You cannot use them broad scale,” Kanoti added.
The forestry service is experimenting with a couple of bio-control beetles. “They are expensive and are a long term solution. They do not have a dramatic impact overnight. Fungal uses are promising, but they are still a ways out. We have limited management now. We do not know what will be available in the long term. Hopefully we can manage them and make an impact,” Kanoti said.
HWA are all females and develop asexually. They produce two overlapping generations per year. Adults immerge from their woolly covering in March and April and lay up to 300 eggs. The crawlers hatch from the eggs in April and May and mature by mid-June and deposit an average of 75 eggs each, which hatch in early July. The egg and crawler stage is the only stage where the pest is not attached, and therefore readily dispersed by wind, birds and mammals, including people. Moving infested plants any time of year can result in the spread of this pest. Live plants should never be moved.
Landowners can prevent the spread of HWA by only harvesting trees when the insect is not mobile. HWA attach themselves to the underside of hemlock by piercing the hemlock and feeding on the juices of the hemlock needles. The best time to harvest hemlock is from August to February when the nymph is attached. When the hemlock is cut, the needles dry out and the adelgid dies.
Kanoti urges landowners to contact the forestry service before “making a knee jerk reaction” and cutting all their trees down.
Currently the only quarantine on hemlock is in York County. To change that, you need to go through a “rule making process,” Kanoti said.
In warmer areas, HWA kills trees in three to four years. “Maine is cold enough” to slow the rate of devastation, Kanoti said.
“Citizen reports are absolutely essential. Our insects and disease folks are terrific, but we do not have the staff to survey intensely, everywhere. As a first step, we need to know where the HWA is,” Morten Moesswilde, MFS Midcoast District Forester said.
The Maine Forestry Service is looking for opportunities to train volunteers to help survey for HWA in the midcoast area, possibly in August. To volunteer, contact the MFS at 536 Waldoboro Road in Jefferson, or by calling 441-2895.
