UMass Extension Landscape Message April 19, 2013
"Winter Moth: Over-wintering eggs began to hatch in SE Massachusetts last week and now most eggs on the southern sides of trees have hatched. Those eggs with northern exposures are lagging behind but progressing towards hatch. Winter moth eggs on Cape Cod are just beginning to hatch as of 4/15/13. Deborah Swanson reports from Plymouth County that tiny first-instar winter moth caterpillars are being found in the swelling/expanding buds of certain host plants, such as apple and crabapple, which indicates that they are most likely to also be found in other host plant buds now, such as maples, that share similar bud-expansion phenology with the Malus species. Winter moth is a problem in Massachusetts on many different deciduous hosts but it is important to note that it does not attack conifers nor evergreens here. Once the caterpillars are within the buds, they are virtually impossible to treat until the leaf tissue fully expands from the bud. At that point, any insecticide that contains Spinosad works well. Bacillus thuringiensis Kurstaki (B.t.K.) also works well but must be ingested by the young caterpillar in order to be effective. Leaves that are not yet fully expanded but treated with a spray of B.t.K. will quickly continue to produce more leaf tissue daily that is not covered by the spray and therefore allowing caterpillars to potentially consume more foliage before ingesting the bacterium. Many pyrethroid insecticides are also labeled for this pest but tend to be harsher on foraging pollinators, such as bees, and other beneficial insects and predatory mites. Overall, winter moth populations are lower in many MA areas this season than in recent years but damaging population levels most likely still exist in random areas of eastern MA. Monitor host plants, swelling buds and eggs closely; this is a critical time for management."