The Japanese beetle, Popillia japonica Newman, is the most abundant and important landscape pest in Ohio. This pest was detected in New Jersey in 1916, having been introduced from Japan. It is common for this pest to be abundant in one part of a town and not others. The adult beetles eat the leaves and flowers of over 300 plants by eating the tissue between the veins, a type of feeding called skeletonizing. The larvae, called white grubs, feed on plant roots and organic matter in the soil, especially under turfgrass. This feeding may result in dead patches of turf that can be picked up like a loose carpet.
from Ohio State University Extension Fact Sheet
Note: The following is a condensed version of The OSU Extension Fact Sheet on Control of Japanese Beetles. I wanted to simply highlight the most important information and leave out the more detailed, scientific parts. For more information please click on the link above for the full article.
The adult beetles normally emerge during the last week of June through July. The first beetles out of the ground seek out suitable food plants and begin to feed. These early arrivals begin to release an aggregation pheromone (odor) that attracts additional adults.
Option 1: Cultural Control – Hand Picking
Kill off the first adults to arrive (these are the scouts that attract additional pests). The adults are less active in the early morning or late evening. They can be destroyed by dropping into a container of soapy water.
Option 2: Cultural Control – Plant Non Attractive Plants
Plant things they don’t like. The adults do not like to feed on 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).
Option 3: Cultural Control – Trapping (not recommended)
Several traps using a floral lure and sex attractant are available. These traps are not recommended for general use unless special conditions can be 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. In most urban areas, traps tend to attract more beetles into the area than would normally be present. In this situation, adult feeding and resultant grub populations are not reduced.
Option 4: Chemical Control – Insecticide Spraying
The adults can be controlled by spraying susceptible plants with insecticides. There are several over-the-counter pesticides available at The Rock Pile. Applications of imidacloprid (Bayer Advanced Tree & Shrub Concentrate) generally need to be made 20 days before anticipated Japanese beetle adult activity. During the heavy adult activity periods, sprays may be needed every 5 to 10 days.
Option 1: Biological Control – Bacterial Milky Disease (milky spore)
The bacterial milky diseases, Bacillus popilliae Dutky, has been quite effective at controlling the grubs in certain areas of the eastern United States. The spore count must build up for 2 to 3 years to be very effective and during this time you should not use an insecticide against the grubs that are needed to complete the bacterium cycle. In Ohio and Kentucky, test trials have not produced satisfactory results. Additional experiments are needed to determine the lack of efficacy of milky disease in these soils.
Option 2: 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.
Option 3: Chemical Controls – Insecticides
The grubs are best controlled when they are small and actively feeding near the soil surface, usually late July to mid-August. However, with the development of new grub control chemistry (e.g., imidacloprid [Merit] and halofenozide [MACH2]), applications in June and July have sufficient residual activity to kill the new grub populations as they come to the soil surface in late July through August. Control of grubs in late-fall or early-spring is difficult, at best, because the grubs are large and may not be feeding. Only trichlorfon (Dylox) and carbaryl (Sevin) formulations are available for such rescue treatments. The key to good control is to make an even application and water thoroughly.