Scientists warn of hemlock parasite

Entomologists are asking property owners to periodically check their hemlock trees for indications that the woolly adelgid is increasing its deadly foothold in Maine.

Maine is on the northern cusp of an infestation of the invasive species that has devastated hemlock groves and some forests up and down the East Coast. To date, the only natural infestations in Maine of the hemlock woolly adelgid – pronounced a-DEL-jid – have been recorded in York County on the state’s southernmost tip.

But the tiny bugs can hitchhike to other parts of Maine on hemlocks shipped from nurseries. If left untreated, the bugs could spread to neighboring hemlocks and start a new infestation.

“People should always be on the lookout for the hemlock woolly adelgid,” said Don Ouellette, forest entomologist with the Maine Forest Service’s Insect and Disease Laboratory in Augusta.

A native of Asia, the hemlock woolly adelgid is a pinhead-sized insect that attacks its host tree by sucking out sap at the base of the needle. Weakened by the adelgid, severely infested trees will eventually drop their needles and die.

The telltale sign of the adelgid is a white, woolly or cottony substance found on the underside of tree branches at the base of the needles.

Ouellette and his staff are aggressively monitoring and treating small patches of adelgid infestations in Kittery, Eliot, South Berwick and York. Trees can be individually treated with a pesticide that is injected into their root systems. Ouellette’s staff members have also released predator beetles known to feed on the adelgid.

Maine’s cold winters likely help inhibit the spread of the adelgid, but this past winter’s mild weather was no help, Ouellette said.

The office also treats and/or removes individual infected trees – normally from nurseries – found elsewhere in the state. Staff members have removed nearly 150 infected trees during the past several years, including some in Bangor, Brewer and Bar Harbor. The most recent infected tree was found in Southport.

Those efforts, as well as a ban on nursery stock from infected counties nationwide, appear to be helping, Ouellette said.

“It’s not going to keep the hemlock woolly adelgid out indefinitely, but it will slow the spread,” he said.

The situation is more serious south of Maine. The woolly adelgid has ravaged hemlock stands in the southern Appalachians and is steadily making its way north. New Hampshire officials, who recently urged residents to be watchful for the bugs, have found the hemlock woolly adelgid in 30 communities since 2000.

If you suspect a hemlock is infested with the woolly adelgid, call the state’s Insect and Disease Laboratory at 287-2431. Information is available online at www.maine.gov/doc/mfs/idmhwa.htm.