UMass Extension Landscape Message April 20, 2012

"Insects

Winter Moth remain active and many are now in the second instar stage (still quite small). Even though some were lost in the high heat of the third week in March and then more lost during the low temperatures of late March, there are still many caterpillars actively feeding right now. Infestations can vary from one town to the next but in more heavily affected areas, the Elkinton lab has discovered between 50-70 caterpillars per Norway maple bud that have only expanded about an inch. These numbers are, of course, astronomical in terms of potential damage to host plants. 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."

Claire