A tree hunt is under way in Southern New England and CELS researchers are hoping they can enlist a posse of sharp-eyed helpers to lead them to eastern hemlocks that can resist the onslaught of a tiny but lethal critter.

Biologist Dr. Evan Preisser and his graduate student Laura Ingwell, along with entomologist Dr. Richard Casagrande and horticulturist Dr. Brian Maynard, have joined forces for the project. They are spreading the word that somewhere out there in the forests there may be trees that are somehow resisting the attack of the hemlock woolly adelgid.

Ingwell will be the point person in this effort, approaching groups of people either by mail or in person asking for help in spotting trees that appear to be resistant to the tiny insects. With the help of the CELS communications office, Preisser and Ingwell have produced a colorful tri-fold brochure that seeks to enlist the help of people who are likely to frequent forests in the region.

Large land owners, hikers, conservationists and birders are among the types of people who will be approached to help with the search.

The brochure is entitled “Have You Seen This Hemlock?” Inside there are photos including a close-up of a hemlock infested with woolly adelgids, tiny insects named for their habit of coating themselves with a white waxy substance. The woolly adelgids attach themselves to the base of hemlock needles and suck out juices. A heavily infested hemlock can be killed in a matter of three or four years.

The idea to conduct the search evolved out of findings by Preisser, who has spent years exploring forests in Connecticut and Massachusetts. Every now and then he found a surviving hemlock in good condition surrounded by hemlocks that were killed by woolly adelgids.

The question arose in his mind: Are those surviving hemlocks naturally resistant to the adelgid? If resistant hemlocks can be found, cuttings from them can be used to produce trees that are naturally resistant to woolly adelgids for reforestation projects.

In a paper that was delivered recently to the Fourth Hemlock Woolly Adelgid Symposium in Hartford, Preisser, Maynard, Casagrande and Todd Caswell (a former graduate student of Casagrande's) stated “there are, as yet, no published records of woolly adelgid resistance to eastern hemlock, but on rare occasions, a relatively healthy tree (referred to as putatively resistant) is found amidst a devastated stand.”

The researchers acknowledge that adelgid susceptibility is influenced by many factors and so they chose to use cuttings from putatively resistant forest trees “in order to grow and evaluate these plants for adelgid resistance under standardized greenhouse conditions.”

That work is being done currently at East Farm and Preisser is hoping to find more sources for cuttings.

Wanted: hemlocks that resist attacks of the tiny adelgid

Graduate Student Laura Ingwell is involved in the search for hemlock trees that may be resistant to hemlock wooly adelgids. In front of her in a URI greenhouse are cuttings from a possible resistant tree. Thousands of other cuttings are being raised at East Farm.

By RUDI HEMPE
CELS News Editor & Reporter

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A key term in the paper is that the researchers are looking for “forest trees.” They do not want hemlocks from prepared landscapes, such as someone’s backyard, because they may have been pampered with irrigation, ample sunlight, fertilizers and pesticides. What they hope to find is what Preisser has found in a few locations—a surviving hemlock surrounded by dead kin.

The trees they are interested for taking cuttings should also be mature—at least 30 feet tall. Ideally they should have deep green needles on full, thick branches, be untreated by pesticides or horticultural oils, surrounded by more than 10 dead mature hemlocks and have few or no adelgids at the bases of needles.

The search is being done at URI even while other institutions are trying to come up with biocontrols.

One possible biocontrol involves the release of a predatory beetle, Laricobius nigrinus. This approach is being tried in Massachusetts and Casagrande says it is possible a similar trial may be done at URI (the campus has a number adelgid infected hemlocks—one is next to the planetarium.)

But, notes Preisser, coming up with an effective biocontrol agent may take many years. If a naturally resistant tree can be replicated through cuttings, this may provide some 'breathing room' for our endangered forests. Propagating seed from a potentially adelgid-resistant tree will not work because the parentage would be uncertain.

Damage to eastern hemlocks is particularly severe in areas like the Great Smoky Mountains National Park and the Appalachians where huge forests have been wiped out. The adelgid does not survive well in severely cold winters and so northern New England has not yet been affected. Climate change, which could result in warmer winters, could change all that.

Western hemlocks, T. heterophylla, are resistant to the hemlock woolly adelgid but many growers prefer the habit of the eastern hemlock and have found it more difficult to grow in the northeast soils and climate. However, some stately 30-foot western hemlocks grace certain areas of East Farm.

“Our goal is to come up with a complementary approach to the problem if bio-controls do not work or if we cannot get western hemlocks to prosper here,” said Preisser. The search for naturally resistant hemlocks is filling in a space that has been overlooked in the war against the adelgid, adds Preisser.

So the hunt is on; anyone who spots a hemlock that appears to be resistant and meets the above-listed criteria should contact Ingwell at 401 874-4083 or hemlock@etal.uri.edu.

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