UMass Extension Landscape Message May 4, 2012

"Winter Moth remain actively feeding in the second and third instar stages. Host plant foliage is now abundant for this voracious feeder. Populations are random and in some cases in large numbers. Recent cool weather has slowed feeding and growth of the caterpillars. Rain events of the past week have pushed foliar growth out quickly allowing the plants to outgrow some of the feeding damage, at least for the time being. Treatments need to be considered on a case by case basis given the recent past weather occurrences that has contributed to egg and caterpillar mortality. For infested plants with opened 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."

Claire