A while back we reported on another threat to New York’s forests. Today, it’s no longer a threat, the menace is here. Last spring while turkey hunting here in the Southern Tier I noticed just about all the hemlock trees are infested by an insect called wooly adelgid. The hemlock woolly adelgid is an aphid-like insect that covers itself with a white, waxy “wool” which acts as a protective coating for the insect. Adelgid infestations are easily recognizable by the appearance of tiny white masses that look like small balls of cotton at the base of hemlock needles.
Eastern hemlock trees are some of the largest and most common trees in many parts of New York and they play an ecologically vital role in cooling mountain streams and providing habitat for many species of birds and animals. The deep shade they provide along creeks creates a cool micro-climate that is critical to the survival of trout and other cold-water species. Scientists say the impact of widespread loss of hemlock could trigger changes more significant than those following the demise of the American Chestnut in the 1930s and 40s.
The insect feeds at the base of hemlock needles sucking the sap which disrupts nutrient flow and causes the needles to change from deep green to grayish-green after which they fall off. Because of this loss of needles the tree starves to death, usually within three to five years of the initial attack. No size hemlock is safe because infestations often start in large, mature hemlocks, but the insect also attacks and kills younger trees as well.
Homeowners with a few hemlocks on their property can take steps to save their trees but in larger tracts, the hemlock trees may be doomed. An ingredient in flea and tick medication called Imidacloprid can effectively eliminate the pest when it is applied to the soil around the base of the tree. When treating a few trees the landowner can temporarily remove the duff of organic matter from around the base of the tree then pour a mixture of Imidacloprid and water on the bare ground around the tree within a foot of the trunk. The duff layer is then replaced. When used in this manner the results have been encouraging. Trees with ashen gray foliage before treatment recover their color and produce new growth. Treatments may remain effective for up to five years. To minimize the risk of impacts to non-target species, the DEC recommends the basal bark spray application method rather than the soil drench, soil injection, or trunk injection methods should be used.
According to information published by the DEC dinotefuran (trade name Safari) is best used as a basal bark spray because it moves more quickly into the tree canopy and thus may be more effective than imidacloprid. However, the report says the treatment is only effective for a single year. Various imidacloprid products have been registered in New York for use as a basal bark spray, a method that is faster and easier than injections. The advantage to using this application technique is that both imidacloprid and Safari can be applied as a mix, thereby affording fast protection for up to 7 years with one application and saving time.
Some states including New York have introduced a predatory beetle that feeds on the insect but, it may take years for them to have a noticeable effect. Here in New York the DEC and partners are releasing Leucopis silver flies collected in the Pacific Northwest for the Hemlock Woolly Adelgid Biocontrol Research Lab at Cornell University to be prepped for release. These are predatory flies that feed on HWA eggs laid in the spring and the release of these flies complements the October 2020 release of Laricobius beetles, another biocontrol that feeds on developing and adult insects during the fall and winter. The goal is to establish stable populations of these predatory flies in the area and provide long-term, year-round protection for the region’s hemlock forests.
To minimize their economic loss some landowners are cutting their stands of hemlock much like what is being done to stands of dead or dying ash trees. It’s not a pretty sight.
Time hasn’t run out for our state’s hemlock trees yet. Hopefully, they won’t disappear like other tree species. We still have time but, is there enough?