Blackstone Parks Conservancy

Providence City Forester Doug Still reports that a large number of trees along the Seekonk River and in Blackstone Park and Swan Point Cemetery have been affected by winter moths. The Boulevard, however, is not doing badly. Intrigued and encouraged by a new treatment of the pest by RI Department of Environmental Management (DEM), Still prefers to wait and see. So far so good.

The dun-colored little moth you may see flying around outdoor lights in November and December looks harmless enough. But the inch-long pale green caterpillar with white stripes running along its sides from which it metamorphosed can chomp through leaf and flower buds at an alarming rate just before or after they open in spring. Many deciduous trees and bushes appeal, and orchards and blueberry bushes are a favorite target.

In a 2013 study of Providence’s urban forest, Still found that 63 percent are potential hosts. Fortunately, most of them are not infested with winter moths—yet. The potential dollar loss if these trees in Providence were to be attacked and defoliated is estimated at approximately $183 million. The pest is active in Rhode Island and rampant in Massachusetts, with some in Maine and southern New Hampshire as well.

Like the invasive plants from Europe and Asis that the Blackstone Parks Conservancy’s Invasive Control subcommittee is attempting to beat back in the Blackstone parks, the winter moth thrives here because it has left behind the predators and diseases of its native area—Europe, in this case. To counter the invasion, two years ago Bruce Payton, Deputy Chief of DEM’s Division of Forest Environment, introduced a fly called cyzenis albicans that prefers to dine on the winter moth. Much as the caterpillar works inside buds, the fly pupae eat the deadly caterpillars from inside in what might be seen as an instance of poetic justice. 

Unlike some other predators that were imported to counteract particular pests, the fly dies off once its prey is gone. In Nova Scotia, which first began encountering the moth in the 1950s, the strategy has worked well for the last ten years without complications. The flies are costly, however. Rhode Island received a $500,000 grant to bring the cyzenis albicans into a limited area, and more will be needed to continue.

Spraying individual trees is feasible, but “we couldn’t possibly spray all of our trees nor would we want to,” says Still. Some toxic sprays can kill bees as well as moths.

“I think that it’s pretty much here to stay,” Still says of  the winter moth. He cites the gypsy moth, which was conquered by disease, as an example of a pest that eventually reached “an equilibrium with the forests.”

Equilibrium is what the Blackstone Parks Conservancy aims for, always keeping in mind our vision: Healthy Urban Green Space for All.


Jane Peterson