Yes, hemlocks (Tsuga canadensis and Tsuga caroliniana) are in grave danger throughout the eastern United States, and Patrick Horan described an overly optimistic scenario in his “Saving Hemlocks” [letter] on Jan. 30. While Horan is correct that biological controls are the best long-term solution to the hemlock wooly-adelgid epidemic, he does a disservice to the effort to save hemlocks by insinuating that chemical treatments are ineffective and overly expensive. The truth is, they are the only method that has been proven to work.
It is clear that we need every available option to combat the hemlock wooly adelgid. Currently, predator beetles are not working, and that may be because the trees they inhabit were very sick before the beetles got there. We need chemical treatments to bring hemlocks up to full vigor and give biological methods a better chance of success. And until biological methods are proven (Patrick Horan [offered] no data, only observations), chemical treatments remain the only sure thing.
Hundreds of thousands of predator beetles have been released in the [Great] Smoky Mountains National Park and adjacent national forests at astronomical costs (beetles used to cost between $2 and $5 each, and now cost [around] 50 cents). There have been no documented successes of predator beetles saving hemlocks. Early “successes” in Connecticut were attributed to a series of exceptionally cold winters rather than beetles. Those groves are now dead, as are groves in Virginia, Joyce Kilmer, Cataloochee Valley, Linville Gorge and the Blue Ridge Parkway that received beetle releases. No matter how badly I—or anyone else—wants beetles like Sasajiscymnus tsugae or Laricobius nigrinus to work, they have not yet. We need to continue to search for biological-control methods that work, including predators, fungi and pathogens. However, we shouldn’t throw chemicals out of our toolbox, especially when they are our most effective and inexpensive tool.
The sad truth is that we have lost the battle with hemlock wooly adelgid in WNC. On a landscape level, hemlocks will cease to play the role they once did. We do have the opportunity to save the last remaining groves. What we do not have is time to experiment with unproven methods.
— Josh Kelly