The Japanese beetle (Popillia japonica Newman) is a highly destructive plant pest that can be very difficult to control. Feeding on grass roots, Japanese beetle grubs damage lawns, golf courses, and pastures. Japanese beetle adults attack the foliage, flowers, or fruits of more than 300 different types of trees and plants.
Adult Japanese beetles feed on broad-leaved trees and plants and can cause significant damage as they defoliate the plants. The grubs will also feed on a wide variety of plant roots, including ornamental trees and shrubs, garden and truck crops, and turf grasses. They seem to prefer Kentucky bluegrass, perennial ryegrass, tall fescues, and bentgrass.
Symptoms of Damage
Adult Japanese beetles are skeletonizers. This means that they eat the leaf tissue between the leaf veins, but leave the veins behind. Attacked leaves have a lacey appearance, and soon wither and die. Adult beetles will often attack flower buds and fruit. The grubs can kill small seedling plants but most commonly damage turf. The turf first appears off-color, as if under water stress. Watering may help temporarily, but more often it will have no effect. The turf feels spongy under foot and can be easily pulled back like old carpet to reveal the grubs. Large populations of grubs kill the turf in irregular patches.
Life Stages of the Japanese Beetle and white grubs
Larvae that have matured by June pupate and the adult beetles emerge from the last week of June through July. The first beetles out of the ground seek out suitable food plants and begin to feed as soon as possible. Newly emerged females release an additional sex pheromone to attract males. The first mating usually takes place on turf with several male suitors awaiting the emergence of a new female. Mating also is common on the food plants and several matings by both males and females is common. After feeding for a day or two, the females leave feeding sites in the afternoon and burrow into the soil to lay eggs at a depth of two to four inches. Females may lay one to five eggs, scattered in an area, before leaving the soil. These females will leave the following morning, or a day or two later, and will return to feed and mate. This cycle of feeding, mating, and egg laying continues until the female has laid 40 to 60 eggs. About 95% of a population are generally laid by mid-August, although adults may be found until the first frost of fall.
If the soil is sufficiently moist, eggs will swell in a few days. The first instar larvae dig to the soil surface, where they feed on roots and organic material, taking typically 17-30 days to mature. While this development is occurring, grubs may tunnel laterally in search of organic matter and fresh roots. This creates a very spongy feel to the soil and turf. The grubs burrow four to eight inches into the soil as cold temperatures arrive. At this depth, the soil rarely gets below 25 degrees F and the grubs survive with no difficulty. If the soil begins to cool further, the grubs may dig deeper. The grubs return to the surface in the spring, as the soil temperature warms. Generally, the grubs can be expected to be active at the surface when the surface soil temperatures are about 60 degrees F, usually in mid-April.
Use Japanese Beetle Traps (see below) to identify the early emergence of the beetles and to reduce the number of beetles. At the first sign of the beetles, spray the area with Bug Buster Pyrethrin Insect Spray. The timing of the initial spraying is important, because females lay the majority of their eggs within the first seven to ten days of their lives. Continue spraying with Bug Buster every seven to fourteen days, to reduce further adult feeding.