UMass Extension Landscape Message April 13, 2012
"Winter Moth remain active but growth rate has been slowed by the much cooler temperatures of the past week. Larvae are either first or second instars and therefore still quite small. For infested plants with opened or opening buds, a spray of Bacillus thuringiensis Kurstaki (B.t.K.) can be quite effective. However, B.t. needs to be ingested by the caterpillars to be effective and if the foliage is not yet near to being fully expanded, then wait for that to happen. Otherwise, the new foliage material that appears over the next several days, after spraying B.t., will not be covered with B.t. thus allowing the caterpillars more leaf surface to damage before ingesting the pesticide. An application of a product that contains Spinosad as the active ingredient should provide excellent results at this time or in the coming weeks during the caterpillar feeding stage. Many pyrethroid insecticides are labeled for caterpillars as well. Avoid spraying apples and crabapples with Spinosad or pyrethroid products if they are in bloom. Pyrethroids can be very harsh on pollinators, such as bees. Spinosad products are toxic to bees at the time of application but this threat diminishes significantly 24 hours after application."