Spot a rosy maple moth resting on the side of a building where it has been attracted by lights, and you might think you are looking at some exotic tropical insect, but rosy maple moths are native insects that occur throughout the eastern U.S. Here in the Deep South, there are two to three generations per year, but only a single generation occurs farther north. The caterpillars, known as green mapleworms, are light-colored with green, longitudinal stripes and feed primarily on maples, and occasionally oaks. Although these insects are relatively common and widely distributed, their numbers are usually low enough that they go largely unnoticed. In relatively rare situations, unusually heavy infestations of green mapleworms cause severe, sometimes complete, defoliation to maple trees in home and commercial landscapes.
Control: If heavy infestations of greenstriped mapleworms threaten to defoliate young maple trees, trees that are still small enough they can be sprayed, these caterpillars can be controlled by spraying with an insecticide that contains spinosad. Spinosad is highly effective on caterpillar pests and “homeowner formulations” containing 0.5% spinosad are readily available at co-ops and garden centers. Insecticides such as cyfluthrin, bifenthrin, acephate or carbaryl will also control mapleworms, but are more likely to trigger outbreaks of other insect or mite pests. Acelepryn (chlorantraniliprole) or Conserve (spinosad) is a better choice for commercial applicators. Larger trees are more difficult to treat. Trees that are completely defoliated may be unsightly for a while but will usually leaf out and recover.