A tree-killing invasive insect, the hemlock woolly adelgid (HWA), was found for the first time in Indiana on a landscape tree in LaPorte County in mid-April.
Since its introduction to the Eastern United States in the mid-1920s, the HWA has infested about half the native range of Eastern hemlock. In certain areas of the Great Smoky Mountains, as many as 80 percent of the hemlocks have died due to infestation.
The finding of the tiny aphid-like insect, which destroys native hemlocks by feeding on the tree sap at the base of the needles, was confirmed by the USDA Animal Plant Health Inspection Service (APHIS). The insect was identified on a single hemlock as a result of a homeowner’s report. The infested tree may have originated from a landscape planting in Michigan and been brought into Indiana about five years ago. Preliminary searches have revealed no other infested trees in the area, but an extensive survey is underway.
“Fortunately, this find occurred outside of the native range of hemlock trees in Indiana, which greatly increases our chances of preventing spread to them,” said Phil Marshall, state entomologist for the DNR.
In Indiana, forests containing hemlocks are scattered throughout the west central and southern half of the state. Evergreen hemlock trees dot the steep slopes along Big Walnut Creek in Putnam County, relics of an earlier, cooler climate. The Nature Conservancy and the DNR Division of Nature Preserves own and manage over 2,000 acres along this creek to protect the hemlock trees, as well as the rest of the forested land. “It’s hard to imagine losing this species from Indiana’s forests”, said Chad Bladow, Director of Southern Indiana Stewardship. “There are already few places in the state where visitors can see hemlocks, and HWA could eliminate all of them”. Other Indiana sites which are well-known for having eastern hemlock include Turkey Run State Park and Shades State Park in Parke County and Hemlock Cliffs in Hoosier National Forest in Crawford County. The Conservancy has acquired lands to help expand each of these sites.
HWA is easily spread by wind, movement on birds and mammals such as deer, but most rapidly as a hitchhiker on infested horticultural material. The best way to protect hemlocks in Indiana from HWA is to simply not buy or plant hemlocks.
“Purchasing plant materials from areas of known HWA infestation are very likely to provide the source of any potential infestation in Indiana,” said Tom Swinford, regional ecologist for the DNR, noting that not every tree is inspected to guarantee it is not infected. “We should do everything we can to protect our unique and beautiful eastern Hemlock trees in Indiana. A visit to the Smoky Mountains shows just how sad and devastating this scourge can be.”
"HWA will be very destructive if it reaches our native hemlocks, but the more people who become aware of the dangers of moving plant material and firewood over long distances, the better chance we have at protecting our forests,” Marshall said.
The Conservancy works to prevent invasive species from taking hold in Indiana. “Prevention is the best medicine when it comes to invasive species,” notes Ellen Jacquart, Director of Northern Indiana Stewardship and coordinator for Invasive species issues for the Conservancy in Indiana. “Don’t buy hemlock for landscaping – choose another native tree instead, and help make sure our native hemlock stands survive.”
Named for the cottony covering over its body, HWA somewhat resembles a cotton swab attached to the underside of young hemlock twigs. Within two years, its feeding causes graying and thinning of needles. Highly infested trees will stop putting on new growth, and major branches die, beginning in the lower part of the tree. Eventually the whole tree is killed.
If you suspect an HWA infestation, call the Indiana DNR Invasive Species Hotline at 1-866-NO-EXOTIC.
The Nature Conservancy is a leading conservation organization working around the world to protect ecologically important lands and waters for nature and people. The Conservancy and its more than 1 million members have protected nearly 120 million acres worldwide. Visit The Nature Conservancy on the Web at www.nature.org.