UMass Extension Landscape Message April 5, 2013

Interesting information on color of eggs and timing of hatch related to Growing Degree Days (see table in message).

"Winter Moth - The over-wintering eggs of winter moth are now loosely scattered on tree bark. They typically hatch from early to mid-April in MA. With these cooler-than-expected temperatures, over-wintering eggs are not yet displaying any signs of maturing toward hatching. New caterpillars seek swelling buds and wriggle in to feed within leaf and flower buds. All maple, apple, crabapple, blueberry, oaks and other deciduous hosts are susceptible. Larvae do blow around on wind currents and often invade via this manner. For blueberry and apples, this can be a very serious pest while feeding within the buds due to the destruction of the flowers. Horticultural oil sprays can be used for these fruit crops just prior to the hatching of the eggs. Winter moth eggs are now an orange-red color but will start to turn to a powdery blue color and then turn to a deep and shiny blue about two days prior to hatching. A chemical insecticide may also need to be applied to target those caterpillars that were not killed by the oil in the egg stage. Once the larvae are within the buds, there are no controls until the buds open and the caterpillars are exposed. At that time, all products that work well on Lepidopteran (moth) caterpillars will work well. Products that contain Spinosad as the active ingredient have been utilized widely in recent years for this pest and are extremely effective. The Growing Degree Day model for winter moth egg hatch has previously been assumed to be 20-50 GDD (base 50) but recent research by the Elkinton lab here at UMass Amherst suggests that a better model for winter moth is to use a base 40, which would result in approximately 180 GDD for egg hatch. The researchers also expect egg hatch to occur in MA after the second week and possibly as late as the third week of April this year."

Claire