Imidacloprid pesticide appears to have eliminated hemlock woolly adelgid from trees injected a year ago in Ohio's Hocking Hills State Park, officals say; forester notes treatment can preserve larger hemlocks in key areas, but will not fully eradicate pest
May 18, 2014
(Columbus Dispatch )
– Ohio says it's winning the battle against an invasive bug that kills hemlock trees -- at least in one place that has a lot to lose.
Almost 700 trees in the northern-most section of Hocking Hills State Park were injected with imidacloprid, a pesticide that kills the woolly hemlock adelgid. The insect is sweeping through the Midwest, threatening millions of trees in its path.
The state treated the trees, near Cantwell Cliffs, a year ago. When forestry experts returned this spring, they were surprised to find that the pest was gone.
"A year after treatment, we were hard-pressed to find (the adelgid) in the area," said Tom Macy, forest-health forester for the Ohio Division of Forestry. "The chemical takes a little while to reach its peak effectiveness. You wouldn't expect to see immediate results."
The hemlock woolly adelgid was discovered in Lawrence, Monroe and Vinton counties in southeastern Ohio in March. The species had been found in Meigs and Washington counties in 2012 and in Hocking County in 2013.
Known for the cottony sac shelters they weave on branches, the aphid-size adelgids feed on the nutrients that hemlocks store at the base of their needles. Adelgids can kill an adult tree in a few years.
Officials say the insects probably came into the United States on hemlocks imported from Japan. They were first found near Richmond, Va., in 1951. They since have spread to 18 Eastern states, from Maine to Georgia. The adelgid is primarily transmitted by wind and birds.
Ohio instituted a quarantine that restricts the movement of hemlock trees and materials out of infested counties and requires growers in non-
infested counties to have materials inspected before they can be shipped.
Experts here also are discussing the use of beetles native to the Pacific Northwest and Asia that eat only the adelgid.
The adelgid's spread is akin to wildfire, said Dave Apsley, a natural-resources specialist with Ohio State University Extension. "You have a front that's spreading, but then you have these hot spots that are way out ahead of the fire."
Hocking Hills is one of those hot spots. "If we allow the spots to boil in front of the front, then the movement of the front is going to be a lot quicker," Apsley said.
Losing southeastern Ohio's hemlocks would be a disaster to tourism, said Rebecca Miller, the president of Hocking Hills Conservation Association. "That's what draws people down here. The hemlocks thrive on the rock outcroppings and cooler temperatures. We have the largest concentration of hemlock stands in the state."
The group runs hemlockhero.com, which sells T-shirts to raise awareness. It hopes to create a database to monitor where the adelgid is found and how to report it.
"I'm sure there are other places that we haven't spotted," Miller said. "We know that it's here and continually coming."
Jesse Webster, forester for Great Smoky Mountains National Park in Gatlinburg, Tenn., has overseen the treatment of more than 250,000 hemlocks in the half-million-acre park.
"The only reason (the trees) are there is because we did something," said Webster, who advised Ohio on its treatment plans. "There's no way we're going to eradicate it. But it is completely doable to preserve some of our larger hemlocks in key areas.
"Ohio has a lot of reasons to be optimistic."