Maine is the most-forested state in the nation, with forests covering almost 90 percent of the state’s land area. But some major components of those forests are being threatened by pests, a fact made abundantly clear at the Grow Maine Green Expo last month in Augusta.

The most immediate threat is the emerald ash borer beetle, which was found in Madawaska and neighboring towns in May and in the York County towns of Acton and Lebanon in September.

State Horticulturist Gary Fish outlined for arborists and landscapers at the Expo the draft proposals for quarantines aimed at slowing down the spread of the pest.

The emerald ash borer attacks all three types of ash trees that grow in Maine, Fish said – green, white and brown or black ash – and it kills 99 percent of the trees it attacks.

“The brown ash, which is most important to native Americans, is the least resistant,” he said. Black/brown ash has been used for many generations in the traditional baskets and other products made by Maine tribal members.

The areas to be quarantined under the draft proposal are all of York County and an area from the western boundaries of Fort Kent, Wallagrass and Eagle Lake eastward to the Canadian border. Nursery stock, firewood made from hardwood trees and green lumber would not be able to leave the quarantined areas unless the wood is certified as free of pests.

The quarantine won’t stop the spread of emerald ash borer, but it should slow it down. The natural spread of the beetle is 2 miles a year, Fish said, although it can fly as much as 10 miles to locate a plentiful supply of ash trees. The quarantine is designed to prevent big jumps, such when someone inadvertently drives wood containing the emerald ash borer from a home in the infested area to a cottage along the coast or a ski camp.

Fish said people who want to protect their ash trees should start preventive treatments when the borer is discovered 10 miles away. Such measures involve injecting the trees or treating the surrounding ground with pesticide, usually systemic.

More than the forests are feeling the effects of the pest, Fish said. When Dutch elm disease decimated the elms that line many streets decades ago, many municipalities replaced them with ash trees. So many municipal street trees could be lost, as well.

Larval browntails eat through an oak leaf.

The quarantine for hemlock woolly adelgid also may be expanded, although the tiny beetle is remaining mostly along the coast – except for a jump to Frye Island, located in Sebago Lake. Fish said the release of predators could slow down the spread of the adelgid. Unfortunately, the arrival of another hemlock pest – hemlock elongate scale – in ornamental trees along the coast spells more trouble for hemlocks.

“Hemlocks can survive quite a while with one of the pests,” Fish said, “but not both.”

Oaks are also being threatened. Aaron Bergdahl, a forest pathologist with the Maine Forest Service, said oak wilt has not yet reached Maine, but it is in New York and moving this way.

The disease – which he said is similar to Dutch Elm Disease in that it is spread by an insect that transports a fungus – was discovered in Wisconsin way back in 1944. The jump to New York, however, was recent.

Red oaks, pin oaks and black oaks are highly susceptible to oak wilt, and when the disease gets into their vascular system the trees can die quickly – in about a month. White oaks are more resistant, in that they take longer to die.

A tree infested with the emerald ash borer.

Bergdahl said that if an oak drops its leaves in large numbers in June or July, the cause is most likely oak wilt. Oak wilt gets into the trees through cuts or wounds, so the best prevention is to avoid pruning during the growing season and to remove infected trees. The trees can also be injected with a fungicide to protect them, he said, a job best done by a professional.

The winter moth and browntail moth continue their presence along the coast, and have killed off trees in several areas. Thomas Schmeelk, an entomologist with the Maine Forest Service, reported that the winter moth has not been as bad for the past couple of years, possibly because a parasitic fly has been released that is killing some of the moths.

The winter moth attacks all hardwoods, not just oak, but oak is among its favorite targets. Spraying trees with dormant oil in late March or early April can keep the moths under control by smothering the eggs, but will not eliminate them. I’ve been doing that, but not as effectively as I could have, as I have sprayed only our high bush blueberries, which I am most concerned about protecting. This year, I plan to spray the trunks of nearby trees, as well, to kill any eggs there.

Browntail moth, which has existed in Maine since 1904, is cyclical, with populations increasing and then collapsing. Populations have been increasing since 2015, Schmeelk said.

The most effective way to control the browntail moths is to remove any webs you can reach (wear gloves) and either burn the webs or put them in soapy water. Do such work between now and late April. Spraying works through the end of May, but is most effective if the entire neighborhood participates.

Since these reports, much of the northern United States has been hit with frigid temperatures which could, temporarily, set back pests. Hemlock woolly adelgid is particularly susceptible to cold, which is part of the reason it has yet to travel beyond Maine’s coastal areas. The emerald ash borer is designed to withstand cold – but still could be slowed, some. But the cold won’t eliminate any of the pests – and as the climate change ensures that the world is getting ever warmer, they will rebound continue to devastate Maine’s trees.

Tom Atwell is a freelance writer gardening in Cape Elizabeth. He can be contacted at:

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