There’s a pest out there that’s destroying some of the most beautiful trees in our landscape. And it has the experts working frantically to find a solution to the problem before it eliminates the eastern and Carolina hemlocks so many of us love.
Legislator Danny Wells first brought this to my attention. He called to tell me about it, and followed his call by sending an informative article from the December 2007 issue of The New Yorker. So I contacted Eric Ewing, plant pest regulatory program supervisor for the West Virginia Department of Agriculture.
“The problem the gentleman was referring to is hemlock woolly adelgid. It is an insect from Asia that feeds on hemlock and only hemlock. Left untreated, the tree will eventually weaken and die. The pest is easy to control in a landscape situation, but treating forest trees is difficult and extremely expensive,” Ewing explained.
“It is killing a lot of trees in West Virginia. Hemlock is one of my favorite trees, so this pest is the one that I despise the most. Unfortunately, like most exotic pests, it doesn’t seem to be going away anytime soon,” he continued.
Native to Asia, the hemlock woolly adelgid (Adelges tsugae) is a small, aphidlike insect that threatens the health and sustainability of eastern hemlock (Tsuga canadensis) and Carolina hemlock (Tsuga caroliniana) in the Eastern United States.
Ewing sent a very helpful pamphlet from the U.S. Department of Agriculture detailing the problem with this insidious insect, and it tells us what to look for when checking our plants for this pest.
“The hemlock woolly adelgid is tiny, less than 1/16-inch (1.5 mm) long, and varies from dark reddish-brown to purplish-black in color. As it matures, it produces a covering of woollike wax filaments to protect itself and its eggs from natural enemies and prevent them from drying out. This ‘wool’ [ovisac] is most conspicuous when the adelgid is mature and laying eggs. Ovisacs can be readily observed from late fall to early summer on the underside of the outermost branch tips of hemlock trees.”
According to the New Yorker article, written by Richard Preston, the pest was brought to the United States by a well-meaning gardener in Richmond, Va., nearly a century ago.
“In 1911, a woman named Sallie Dooley established a Japanese garden at Maymont, her estate in Richmond, Va. She planted bamboo, built a gazebo and a waterfall, and, according to her husband, James Dooley, a financier, ‘purchased the most costly evergreens from all parts of the world.’ She died in 1925, and Maymont was left to the city of Richmond. It became a park, and the Japanese garden went unattended. In 1951, an entomologist with the Virginia Department of Agriculture discovered a species of Asian insect known as the hemlock woolly adelgid infesting an eastern hemlock — a tree native to North America — on property near Maymont park.
“The suspicion was that it had come from Sallie Dooley’s imported evergreens, though no one could be sure. Experts considered it a curiosity,” the article continued.
The Department of Agriculture suggests the following for control in our gardens.
“Cultural, regulatory, chemical and biological controls can reduce the hemlock woolly adelgid’s rate of spread and protect individual trees. Actions such as moving bird feeders away from hemlocks and removing isolated infested trees from a woodlot can help prevent further infestations. State quarantines help prevent the movement of infested materials into noninfested areas.
“Chemical control options, such as foliar sprays using horticultural oils and insecticidal soaps, are effective when trees can be saturated to ensure that the insecticide comes in contact with the adelgid. Several systemic insecticides have also proven effective on large trees when applied to the soil around the base of the tree or injected directly into the stem. Chemical control is limited to individual tree treatments in readily accessible, nonenvironmentally sensitive areas; it is not feasible in forests, particularly when large numbers of trees are infested. Chemical treatments offer a short-term solution, and applications may need to be repeated in subsequent years.”
“What does the winter season offer the gardener? Little, it may first be thought. And yet this is not the truth. First, there is during the closed months time to meditate upon our mistakes and failures (which have doubtless been many) and to seek some ways to remedy them .... And then there is remembering: remembering the bold scarlet of the Poppies in June, the towering spires of the Delphiniums .... And forgetting! Forgetting is perhaps as important as remembering. If we are to start the new season with vigor and enthusiasm, we must forget the backaches, the loathsome prevalence of slugs and other pests, the superiority of our neighbor’s Sweet Peas and Asters, and certain humiliations suffered from the behavior of various sniffy alpines that turned up their small toes and died in the face of our most earnest ministrations.” — L.B. Wilder, “The Garden in Color” (1937)
Sara Busse is a Charleston resident and master gardener. She may be contacted at sjbu...@gmail.com.