Special to the OBSERVER
Of all the invasive species that invade our gardens every year I believe that the Japanese beetle (Popillia japonica Newman) is the worst. First discovered in 1916 in NJ, where they had hitchhiked a ride from Japan on Iris roots, they have now spread to all states east of the Mississippi River except Florida. The beetles attack some 250 different ornamental plants, trees, shrubs, turf grasses and agricultural crops.
The Japanese bettle.
The adults start to emerge from their larval stage in the soil starting in late June and promptly begin to feed on the leaves of plants giving them a skeletonized appearance. They feed on the upper leaves and work their way down. Mid- morning to late afternoon is when they are most active. As they feed on plants, the beetles give off an aggregation pheromone which attracts more beetles and to make matters worse, the females give off a sex pheromone that attracts the males. This explains why your plants are soon covered with Japanese beetles.
The adults are a metallic green with copper colored wings and they are 3/8" long and " inch wide. The larvae are C shaped, white in color and about 1 inches long when mature. After the females have mated they begin laying eggs in the top 2-4 inches of soil, up to 60 eggs are laid during the summer. Once the eggs hatch, the larvae dig into the soil eating roots and organic matter; they typically go through three instar stages by September. In October, they begin to go deeper into the soil to overwinter. When the soil starts to warm again, around mid-April, they migrate to the top 3-4 inches of soil where they finish their development as a pupa in an earthen shell.
There are several ways to control Japanese beetles but CONTROL is the key word as total eradication is next to impossible.
CONTROL of ADULT BEETLES
Monitor your plants for early arrivals starting the end of June. Early morning or late evening is a good time to do this as they are less active. If you are not squeamish squish them or place them in a jar of water with some dish soap and dispose of them. I feed mine to the chickens and boy do they gobble them up.
Plant non-attracting plants:
There are lots of plants that are not attractive to Japanese beetles: ageratum, arborvitae, ash, baby's breath, garden balsam, begonia, bleeding heart, boxwood, buttercups, caladium, carnations, Chinese lantern plant, cockscomb, columbine, coralbells, coralberry, coreopsis, cornflower, daisies, dogwood (flowering), dusty-miller, euonymus, false cypresses, firs, forget-me-not, forsythia, foxglove, hemlock, hollies, hydrangeas, junipers, kale (ornamental), lilacs, lilies, magnolias, maple (red or silver only), mulberry, nasturtium, oaks (red and white only), pines, poppies, snapdragon, snowberry, speedwell, sweet pea, sweet-William, tuliptree, violets and pansy, or yews (taxus).
This method is not recommended unless certain conditions are met. The traps have been demonstrated to be effective in reducing damage and populations only when landscapes are isolated from other Japanese beetle breeding areas or when mass trapping (everyone in the neighborhood) is used.
Chemical Control-Insecticide Spraying:
The adults can be controlled by spraying susceptible plants with insecticides labeled for adult Japanese Beetles. During the heavy adult activity periods, sprays may be needed more frequently. Follow the pesticide label instructions carefully.
CONTROL of GRUB STAGE
Biological Control-Bacterial Milky Disease:
The bacterial milky spore disease, Bacillus popilliae Dutky, has been quite effective at controlling the grubs in some areas of the eastern United States. The spore count must build up for 2 to 3 years to be effective; during this time you should not use an insecticide against the grubs. As the spores spread in the soil, they are swallowed by the grubs during their normal root feeding. Once inside the grub, the spore begins to reproduce; this kills the grub within 7-21 days and during decomposition of the grub billions of new spores are released into the soil.
Biological Control-Entomopathogenic Nematodes:
Insect parasitic nematodes have recently become commercially available. Products that contain strains of Steinernema carpocapsae (Biosafe, Biovector, Exhibit, Scanmask) have been marginally effective against white grubs in turf. Preparations containing Heterorhabditis spp. seem to be more effective. Apply the nematodes when the white grubs are small. Irrigate before and after applying the nematodes.
The grubs are best controlled when they are small and actively feeding near the soil surface, usually late July to mid-August. Control of grubs in late-fall or early-spring is difficult, at best, because the grubs are large and may not be feeding. The key to good control is to make an even application and water thoroughly.
Carol Sitarski, Cornell University Cooperative Extension, Master Gardener