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Forest Fungus Factory

July 22, 2011

By Joshua E. Brown, University of Vermont

Hemlock is the third most common tree species in Vermont. But it soon may drop off the list, going the way of the now-vanished chestnut and elm. An invasive pest, hemlock woolly adelgid, has been marching and munching its way north along the Appalachians “” killing pretty much every hemlock it can sink its sap-sucking mouthparts into. The adelgid recently arrived in southern Vermont.

So far, only extreme cold stops the hemlock woolly adelgid. But the University of Vermont’s Scott Costa may soon give forest managers and homeowners a tool to fight back.

Working with the U.S. Forest Service, the State of Vermont, and others, Costa, an entomologist in UVM’s Department of Plant and Soil Science, has been developing a novel method of putting an insect-killing fungus, lecanicillium muscarium, to work protecting hemlock trees.

The entire range of eastern hemlock and the less common Carolina hemlock, from southern Canada to Georgia, is currently at risk from the adelgid, a bug native to Asia that arrived in the United States in the 1920s and made its way to the East Coast in the 1950s. The stakes are high: hemlock provides habitat for dozens of mammals and birds. Arching over streams, it creates deep shade critical for the survival of trout and other fish. Some scientists think hemlock is a so-called keystone species, holding up a whole ecosystem.

Nobody thinks the adelgid pest can be eliminated. But Costa has had success with field trials on one-acre forest plots in Tennessee, using helicopters to drop the fungus “” mixed with his proprietary blend of growth-enhancing ingredients “” into the epicenter of the adelgid’s devastating attack. These trials reduced the growth rate of adelgid by fifty percent “” “that’s the first time that’s been demonstrated with an insect-killing fungus,” Costa says “” and it seems likely to give trees a fighting chance of recovery.

Over the last year, Costa has been testing the same technology on single trees in Vermont to see if ground-based spray applications will work, too. UVM Today dropped in on Costa in the field at Townshend State Park, north of Brattleboro, Vt., and in his laboratory at Jeffords Hall on campus. We wanted to see if his latest experiment would succeed.

Image Caption: Evidence of Hemlock Woolly Adelgid on Hemlock. Credit: Connecticut Agricultural Experiment Station Archive, Connecticut Agricultural Experiment Station / © Bugwood.org / CC-BY-3.0-US

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