Start receiving our award-winning magazine today!


Public, Private Partners Set Out to Protect Hemlock Trees from Destructive Pest

Cranesville Swamp Treated for Hemlock Woolly Adelgid

BETHESDA, MD | May 14, 2014

Cranesville boardwalk_490x250 

Foresters, entomologists and ecologists from various partnering organizations joined forces to combat an invasive pest the size a pencil tip that threatens to wipe out eastern hemlock forests—a loss that could be as ecologically significant as the loss of the American chestnut.

For the past several weeks, the USDA Forest Service partnered with the Maryland Department of Agriculture’s Forest Pest Management Section, Maryland Department of Natural Resources (DNR), West Virginia Department of Agriculture's Plant Industries Division (WVDA) and the West Virginia and Maryland/DC chapters of The Nature Conservancy to treat a mature stand of hemlock trees for hemlock woolly adelgid (HWA) on the Conservancy’s Cranesville Swamp Preserve in Garrett County, Md. and Preston County, W.Va. Hemlock woolly adelgid is an exotic insect native to Japan that feeds on hemlock sap, ultimately killing the trees. Although it was first discovered in Virginia in 1951 and has been affecting hemlocks across the northern United States for years, it wasn’t detected in Cranesville Swamp until 2012.

“If we don’t go after this invasive species, we stand to lose hemlock trees throughout Maryland and West Virginia, which would seriously disrupt the ecology of the area,” said Deborah Landau, conservation ecologist for The Nature Conservancy’s Maryland/DC chapter. “There’s simply no ecological equivalent to hemlock in this area and with this keystone tree species we stand to lose a number of rare and significant plant and wildlife species.”

The public/private partners treated about 600 trees using a combination of methods to treat the tree and/or the soil around the trees in a 100-acre stand of hemlocks in Cranesville Swamp. Treatments included stem injections of trees within 50 feet of a water source, soil injections and tablets for trees away from a water source.

“This is a great collaboration among five public/private partners for a special conservation effort,” said Agriculture Secretary Buddy Hance. “The HWA does most of its damage in May and June, and again in the fall. We have been successful at curtailing its damage and saving our hemlock trees over the past 10 years. We will continue to do all we can to get in their way, and protect threatened trees and their associated ecosystems on public lands and private lands as funding is available.”

Cranesville Swamp is in a frost pocket that runs several degrees cooler than the surrounding area and is home to a number of species not found elsewhere in Maryland or West Virginia. In total, more than 50 rare plants and animals live there. Cranesville’s trees and wetlands also act as natural filters, helping provide surrounding communities with clean water. DNR staff worked with TNC to delineate the ground seeps and drainages throughout the hemlock stand, to ensure that the proper insecticide application technique was used in more sensitive areas.

“HWA was first detected in West Virginia more than 20 years ago, so we know this invasive pest well, and have spent many years protecting our valuable eastern hemlock population,” said West Virginia Commissioner of Agriculture Walt Helmick. “We were glad to join this collaborative effort, especially in such a unique place as Cranesville Swamp, to put our best efforts forward to save this hemlock stand.”

The Nature Conservancy contacted the State of Maryland for assistance with this project. Through existing grant funding from the U.S. Department of Agriculture Forest Service, DNR provided the insecticide and MDA and WVDA provided the staffing and equipment to treat the hemlock trees with assistance from Forest Service and The Nature Conservancy staff.

“Made possible by the US Forest Service, this funding is specifically designated for combating invasive species in forested hotspots of biological diversity. This project made terrific use of our grant money, supporting a coordinated effort to save and protect one of Maryland’s beautiful natural areas,” said DNR Invasive Plant Ecologist Kerrie Kyde.

Hemlock woolly adelgid has slowly spread along the east coast resulting in hemlock decline and death. Hemlock woolly adelgid was found in landscaped hemlocks in the Baltimore and metropolitan Washington areas in the 1980s and has spread to natural stands across central Maryland, finding its way to Garrett County by 2001. As a result, MDA, along with DNR, developed a Hemlock Woolly Adelgid Management and Suppression Plan to proactively treat thousands of hemlock trees on public lands with soil and tree insecticide injections— funded by a U.S. Forest Service federal grant program.

(Cranesville Swamp Preserve boardwalk.  Photo © Kent Mason)

The Nature Conservancy is a leading conservation organization working around the world to conserve the lands and waters on which all life depends. The Conservancy and its more than 1 million members have protected nearly 120 million acres worldwide. Visit The Nature Conservancy on the Web at

Contact information

Lindsay Renick Mayer
(202) 422-4671

We’re Accountable

The Nature Conservancy makes careful use of your support.

More Ratings

x animal

Sign up for Nature eNews!

Sign Up for Nature e-News

Get our e-newsletter filled with eco-tips and info on the places you care about most.

Thank you for joining our online community!

We’ll be in touch soon with more Nature Conservancy news, updates and exciting stories.

Please leave this field empty

We respect your privacy. The Nature Conservancy will not sell, rent or exchange your e-mail address. Read our full privacy policy for more information. By submitting this form, you agree to the terms of use.