Fungal factories may save hemlock forests
Reaching into a box glowing with fluorescent light, Stacie Grassano pulls out a tube. “This is a great one,” she says, holding the clear plastic up to her face. Inside, a tree branch is speckled with white fluff. “It's growing really well,” she says, handing it to Scott Costa.
Costa brings the branch close to his eye. “Yes,” he says, with a boyish grin, “this is a fungus success story.”
For some, a fungus success story means nothing is growing at the back of their refrigerator. But for Costa, research assistant professor of plant and soil science at the University of Vermont, and Grassano, his graduate student, the vigorous growth in their laboratory of this fungus, a strain called Lecanicillium mucarium, means a hopeful new chapter in the otherwise bleak tale of the eastern hemlock tree.
From Georgia to Maine, this once-mighty conifer is now succumbing to an exotic pest, hemlock woolly adelgid. First detected in the western US in 1924, the adelgid reached Virginia in the 1950s. An aphid-like insect, the adelgid kills eastern hemlocks within a few years after infestation, feeding on the sap at base of their needles and cutting off their nutrients.
While the adelgid, originally from Japan and China, appears to have no successful predators in North America, some native fungi—like the one Costa and Grassano have growing on branches in their laboratory—kill the pest.
Last December, Costa, Grassano, and two the other researchers, Vladimir Gouli and Jiancai Li, submitted a provisional patent for a new method of cheaply and effectively spreading the fungus, and other similar “biological controls,” that might beat back the adelgid without having to use expensive, toxic pesticides. They call their approach a “whey-based fungal micro-factory.”
Instead of growing fungi in a conventional factory and then transporting it out to a forest—a costly proposition—their factory will be the forest. Or, more accurately, tiny droplets of sweet whey—a cheap waste product of cheese production, inoculated with the right concentrations of the target fungus—will be their factory. By spraying the whey solution into an infected forest, they believe they can get the adelgid-killing fungi to reproduce in large numbers on its own.
“The sweet whey only costs 32 cents a pound,” says Costa, who gets his donated from a New York-based cheese company, and receives support for his research from the USDA and EPA and other funders.
Whey is a far cheaper growing medium than those available in labs for the many fungi now in use as biological controls in agriculture and forestry.
And the whey serves as a nutritional resource, making each droplet a cozy biological factory for a fungal colony, pumping spores out into the forest long after the spraying teams have gone home.
If their laboratory tests continue to go well, the researchers anticipate starting field trials in 2008.
Their approach looks promising for many other applications of biological control for agriculture and forestry—especially in natural settings with economically low-value plants, like natural forests.
“We're not going to eradicate the adelgid,” Costa says. “The best-case scenario for an insect-killing fungi is you inoculate the environment and get disease outbreaks to start cycling. The idea is to reduce the pest population to a level that is manageable, allowing some of the trees to make seeds, grow, and survive.”
It's a pressing problem: In Shenandoah National Park most of the famous towering hemlocks are now dead. The adelgid has ravaged parts of Kentucky, North Carolina and the Smoky Mountains. Expanding northward, it has moved through Massachusetts into southern Maine and New Hampshire.
The only natural deterrent to the adelgid seems to be a very cold winter. With global warming, their northward spread seems inevitable. Though not officially recorded yet, “it's probably in southern Vermont now at population levels too low to easily detect,” say Costa, who anticipates that the adelgid will be into Vermont's Champlain Valley in not too many years.
While the era of cutting hemlock for the tanning industry is over, there continues to be use of the tree for fiber and construction, and commercial forest owners have something to lose with the demise of the hemlock. But far more important, as the hemlocks expire they take an ecosystem down as they fall.
In cool hollows and along shady mountain streams the hemlock has grown for millennia where other trees wouldn't thrive: a quiet giant soaring to over 150 feet. With a range from Alabama along the Appalachians into the Canadian Maritimes, its shaggy crown creates a blueish green haven unmistakable to turkeys and deer (and hunters): a thick understory of duff, deep with shade that accentuates the black furrows of the hemlock's tannin-rich bark.
In winter, chickadees eat the small seed cones of the hemlock and they are only one species of many that depend on the hemlock not just for food but for the architecture of their world. Some warblers only nest in hemlocks and the mountain fish depend on the trees to keep streams cool.
“See all this white growth?” Costa says in his UVM lab, tracing his finger above the soft flat needles. “That's mycelium and likely as not there are spores at the end of each of those.” To the untrained eye, the fungus he and Grassano are growing looks much like the pest they hope it will fight. Hiding on the underside of hemlock branches, the pest produces a white woolly tuft that gives it its name. The fungus looks white and woolly too. But the subtle difference may mean life or death for the eastern hemlock.
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