Massachusetts and other New England states have long been plagued by invasive pests that feed on native vegetation, particularly trees. Such invasive insect pests include the Asian longhorned beetle, the emerald ash borer, the winter moth, the Hemlock woolly adelgid, the brown marmorated stink bug and many more. With the exception of the brown marmorated stink bug, invasive tree pests in the northeast limit their destruction to natural sources of wood within uninhabited forested areas. While the damage these invasive insects inflict onto trees is both a serious environmental and economic problem, Massachusetts residents are not usually faced with indoor infestations of these insect species, but they can infest residential trees. Unfortunately, one invasive beetle species, the Japanese beetle, has become the most common, and therefore, the most destructive insect pest species within residential lawns and gardens in Massachusetts.

The Japanese beetle was first documented in New Jersey back in 1916, and it did not take long before Americans in the northeast discovered this insect’s destructive potential. When beetles are in their larval stage they are referred to as “grubs,” and the Japanese beetle inflicts damage during this developmental stage. Japanese beetle grubs have become the most abundant grub species within New England lawns, and they are believed to account for 90 percent of all grub species existing on Massachusetts lawns. These grubs feed on 300 different types of trees, shrubs, grass, field crops, and garden plants. The grubs eat flowers, many types of fruits and they are known for “skeletonizing” plants by consuming all of their leaves. Their eating habits become particularly voracious on warm sunny days when they eat the routes of plants and grass, and their damage appears in the form of dark patches on lawn grass. The beetle grubs are active in Massachusetts lawns during April and May and again in between August and October. Around 1,500 grubs can become active within each square yard of grass, but in order for a lawn to maintain good health, no more than ten Japanese beetle grubs can be active per square foot. The grubs are difficult to eradicate without professional assistance due to their cryptic tunneling activity beneath the soil’s surface.

Have you ever found seemingly inexplicable dark patches on your lawn?