The Carlisle Mosquito Online

Friday, January 7, 2005


Tree Talk: Hemlock woolly adelgid

Experts believe that this Asian pest will ultimately destroy all of our native Eastern hemlocks here in Massachusetts. It's bad. Below is a quick summary of what it is, status in our area, control measures for landscape trees and hopes for the long term.

The Hemlock Woolly Adelgid (HWA) is a very small aphid cousin. It sucks sap from early fall to late spring, interrupted only by severe cold. The cottony egg masses produced on the underside of new hemlock twigs are distinctive and make identification easy. Reproduction is so rapid and natural predators so absent that large, healthy trees can be killed in 3-4 years. There is debate as to how adapted they are to our weather. They seem to have been set back a bit from last winter's cold spell but unfortunately there is also evidence that the species is evolving. HWA is around Carlisle, it just hasn't gotten into full swing. Yet.

Current controls include well-timed spraying of horticultural oil or use of a systemic insecticide that can be either trunk injected or applied to the roots through the soil. Early detection is important but "landscape" trees can be saved by either well-informed homeowners or licensed professionals. For wild hemlocks long-term hopes rest on the successful adaptation of insect predators such as the Asian Ladybird beetles that were released around Walden Pond in 2002. Like the elm and chestnut there are crossbreeding programs to develop resistant cultivars from other native and non-native hemlocks species and perhaps from yet undiscovered resistant Eastern hemlocks.

My daughter and I have climbed a neighboring hemlock on a couple of warm afternoons. Emerging from the dark under-story we set our final lanyard clip somewhere between losing our nerve and the very top. Then we talked, snacked and enjoyed the view. I try not to worry too much about the tree's fate. Like everything else, enjoy it while you can. Nature rebounds. Maybe someday her child will climb a huge American chestnut.

2005 The Carlisle Mosquito