UMass Extension Landscape Message March 29, 2012

"Winter Moth (WM): Activity of the adult moths last November and December was quite extensive in MA and Rhode Island. High numbers of over-wintering eggs have been observed on host tree trunks. The temperatures of this past winter have been well above the norm for southern New England and much speculation has occurred as to the fate of winter moth eggs: will they hatch too early and be greatly out of synch with their host plant buds? Was it warm enough to have killed the eggs? Will a frost after hatching lead to high mortality of the young caterpillars?

The research lab of Dr. Joe Elkinton at UMass Amherst reports that winter moth eggs began hatching in the greater Boston area on March 21st, then appeared to stall for 1-2 days with hatch resuming on March 23rd with approximately a 50% hatch occurring. By Sunday March 25th, winter moth hatch was near 80% complete on the north and south shores in MA but at less than 5% on Cape Cod. As of this writing, night temperature for March 26 was in the teens (Fahrenheit) in some parts of MA and the effect of this on the tiny caterpillars is yet to be seen. Plant phenology in areas with high winter moth populations varies: Overall, apple is at green tip, some maples, such as red and silver maple are blooming and have swelling vegetative buds which should provide enough food, oaks are still in tight bud and mostly unavailable to the caterpillars. Overall, tree buds on Cape Cod are still mostly tight. Observations in Southeastern MA suggests that eggs on the southwest sides of trees have been desiccated, most likely from the excessively warm days in March and the intense exposure to the sun. Much is still unknown concerning winter moth survival and potential for tree damage given the very atypical weather pattern of this past winter. Those caterpillars that survive can be treated with a product that contains Spinosad as the active ingredient once the foliage buds open or with one of the registered and properly labeled pyrethroid products."

Claire