When you gaze out at our mountains in the winter, the magnificent dark green groves of eastern and Carolina hemlocks used to stand out against the winter browns of deciduous trees. However, you may notice a decrease in green as these hemlocks are fighting a 
somewhat losing battle with the invasive hemlock woolly adelgid (HWA) – a tiny aphid about the size of a poppy seed that sucks the sap from the needles of the hemlocks. Foresters estimate that this tiny insect may have already killed nearly 80 percent of our southern hemlocks. Infected trees are easy to spot from the white cottony egg sacs that cling to the smallest twigs.
But, there is hope. The Hemlock Restoration Initiative (HRI), headquartered in Asheville, is working with a variety of partners to restore hemlocks and sustain their long-term health throughout North Carolina, ensuring that both the eastern and Carolina hemlocks can withstand attacks by the invasive HWA and survive to maturity on public and private lands, including places like The North Carolina Arboretum.
Right now the primary treatment for infected hemlocks is chemical – injecting a systemic pesticide into the ground underneath affected trees. But this approach is costly and temporary; it buys time but does not provide a permanent cure. HRI and its partners are now looking at more permanent solutions. Scientists such as Ben Smith of the Forest Restoration Alliance in Waynesville and Albert Mayfield of the U.S. Forest Service Southern Research Station in Asheville are currently working on several fronts, including:
- Building the knowledge base on the physiology of hemlocks and how they respond to severe conditions such as HWA, drought, air quality and warming temperatures
- Breeding hybrid species that have greater resistance to the HWA, starting with developing a cross between the Carolina hemlock and a Chinese hemlock, and by finding resistant individual trees in the forest
- Developing forest restoration techniques to give new seedlings the best chances of success
- Studying the potential for biological control by introducing insects that will prey on the HWA; two promising species from the Pacific Northwest are a beetle (Laricobious nigrinus) and a predatory cousin of the eastern silver fly.
Want to know more? The Blue Ridge Naturalist Network will present a program entitled “Save the Hemlocks” on February 21, 2017, from 5:30-7 p.m. at the West Asheville Library. Margot Wallston and Sara deFossett of the Hemlock Restorative Initiative will discuss where we stand now with the hemlocks and ways in which these magnificent trees can be saved. This presentation is free and open to the public.
About Blue Ridge Naturalist Network
The Blue Ridge Naturalist Network is an outgrowth of the Arboretum’s Blue Ridge Naturalist (BRN) certificate program. Although not affiliated with the BRN certificate program, many of the network’s members are students, instructors or graduates of the program. The purpose of the network is connecting people who love the natural world. Through meetings and outings, the network focuses on issues surrounding nature and the environment, with a foundation based in science.