Winter was mild — and these pests loved it
Hemlock woolly adelgid (HWA), a pest that was first detected in Virginia in 1951, is believed to have originated in Japan where they caused little damage to trees that have built up resistance. However, untreated infestations in the United States, where they have no natural enemies except for cold winters, the pest can damage or kill both the eastern Canadian hemlock and Carolina hemlock trees, according to U.S. Forest Service data.
Kirk Titus of Bartlett Tree Experts in Wolfeboro first discovered HWA on a landscaping tree brought onto a lot on Wolfeboro Neck about 10 years ago. Upon further inspection, he found four or five more trees. State experts confirmed the trees were infested. The trees were cut down and burned on site.
More recently, Bartlett Tree Experts arborist Lucas Hubbard discovered another infestation a few weeks ago on a nearby lot. Titus said that infestations are treatable, if detected early enough. Left untreated, however, the insects are devastating to hemlocks.
“It can kill trees. It's a very bad pest,” he said in a recent interview, “but it's fairly easily controlled. Left untreated, HWA infested trees die within a few years.
Infestations have been detected in Rochester, Alton Bay, Farmington, Tuftonboro Neck and Wolfeboro Neck.
“The good news is that those populations of trees are healthy,” said forest entomologist Kyle Lombard, who is with the New Hampshire Division of Forests and Lands.
Lombard said HWA was first detected in Portsmouth in 2000.
“For a while, our winter temperatures were holding back the infestations,” he said, adding that the insects don't usually survive cold winters. On the other hand, they seem to be adapting to colder temperatures.
“With insects, climate change is a slow process compared to insect evolution, so insects adapt a lot quicker. About 20 percent of insects lived through the winter and are nowmuch more cold-hearty. The next generation will be even more cold-hearty. That process is happening.”
Last winter's mild temperatures fostered the pest's survival.
In a “normal” winter, Lombard said, he expects a 75 to 90 percent mortality rate for HWA infestation.
“It will balloon this year. Last winter, we had 20 percent mortality, so 80 percent made it through,” he said.
Lombard said the adelgid's are tiny, “the size of a grain of pepper.” What people usually see infesting branches are the white, cottonball-like fluff the insects create at the base of the hemlock needles.
Lombard said the pests could have been brought in on tree nursery stock from down south, and carried on the talons of birds.
“Birds are, by far, the biggest vectors,” he said. “We have roughly 30 towns with infestations in southern New Hampshire.
“Only two of those sites have trees that are close to death. The rest have been treated or are on such good soils they'll survive,” he said.
Lombard advice to homeowners is to keep birdfeeders away from hemlock trees to help prevent infestations; those that choose hemlock trees in their landscape plans should also consider if the lot had high quality soils and an appropriate planting site to keep the trees healthy.
Treatments include non-pesticide approaches, such as a foliage spray made from horticultural oil and soap that can be injected into the trees and/or soils and absorbed into the trunk.
Titus of Bartlett Tree Experts said the company, a national company with extensive experience treating infested hemlock trees, has a 300-acre research facility in North Carolina.
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Larissa Mulkern may be reached at LMulkern@newstote.com.
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