By Ted Waddell
NARROWSBURG — December 2, 2003 – You can hardly see them, as they’re about the size of the head of a pin, but legions of tiny insects called the Hemlock woolly adelgid (HWA) are chomping down lots of hemlock trees.
Recently, a public workshop sponsored by the Upper Delaware Council (UDC) and the National Park Service (NPS) titled “Battling the Hemlock Woolly Adelgid” was held at the Tusten Town Hall meeting room in Narrowsburg.
The stated objective was to inform area landowners on both sides of the Delaware River about the scope of the problem, describe how to detect HWA and present information on management/treatment options.
According to Don Hamilton, resource specialist with the NPS Upper Delaware Scenic and Recreational River (UPDE), the Hemlock woolly adelgid (Adelges tsuga), a small, aphid-like insect whose color varies from dark green to black, is creating a serious threat to the health of Eastern hemlocks (Tsuga canadensis) and the ecosystem of the Upper Delaware.
“Eastern hemlocks dominate many ravines of tributaries that flow into the Upper Delaware River, providing shade, cooler water inputs and stabilizing these streams’ hydrologic regimes while making them less likely to dry up during the summer months,” he said.
Adelgids feed at the base of hemlock needles by extending a long proboscis – think of a period-sized insect with a really long “nose” – into the needle to extract nutrition, causing the needles to desiccate (dry up), turn color and drop from the tree, usually within a few months.
In as little as four years with heavy infestation, defoliation and mortality can follow, causing the death of the most shade-tolerant tree on the East Coast, some of which have witnessed the passing of 400 seasons.
HWA is a non-native insect, believed to be native to China and Japan. Experts think it was brought to North America on imported ornamental hemlock trees. It was discovered in the western states in 1924.
It was first reported on the East Coast when HWAs were found on trees in Richmond, Virginia sometime around 1950.
Since then, it has spread into 12 states. It also attacks Carolina hemlock (Tsuga caroliniana), a rare species found in isolated regions of Virginia, the Carolinas and Georgia.
According to published reports by the scientific community, the main front of the HWA infestation is advancing at the rate of an estimated 15 miles per year.
At present, based upon studies conducted by the U.S. Forest Service, HWA is established in the mountains of the Shenandoah Valley, spreading southward along the Blue Ridge Mountains and north to the mid-Hudson River valley and southern New England.
Jason Denham, a forester with the NYS Department of Environmental Conservation (DEC), said HWA was first detected in the state in 1985 and now infests 20 counties, including Sullivan.
“They look like tiny little specks of pepper,” he said.
White, cottony sacs at the base of the needles are evidence of a HWA infestation.
The destructive insects feed throughout the year, with the greatest damage occurring in the spring. They are dispersed by wind, birds, mammals and humans walking through the woods.
In the forest, the best hope of controlling HWA populations is by the introduction of natural enemies such as parasitoids, insect predators and pathogens.
Individual ornamental trees or larger hemlocks can be treated with chemical insecticides, either by spraying or by injections into the trunk or soil surrounding the root systems.
For more information about the HWA, call the UDC at 252-3022, NPS at 570-729-7842 or NYS DEC at 518-402-9425.