AGRICULTURE

Japanese Beetles

June 1996

Japanese Beetles, (Popillia japonica) the most widespread and serious turfgrass insect pest in the Northeast when it is a grub, is also a major pest as an adult, when it feeds on nearly 300 species of plants, including fruits, vegetables, ornamentals, field and forage crops and weeds. The grub is a major turfgrass pest of golf courses, recreational and industrial parks, school grounds and home lawns.

Adult Feeding: Adults cause no injury to turf but are an important pest of many other plants. Of the nearly 300 species of host plants, the most favored include apples, cherries, grapes, peaches, plums and blueberries in fruits; asparagus, beets, broccoli, rhubarb and sweet corn in vegetables; maples, birch, crabapples, roses, sassafras, mountain ash and linden in ornamentals; soybeans, alfalfa, clovers and corn in field and forage crops; and smartweed, crabgrass, ragweed and cattail in weeds.

Members of the Rose family are highly attractive host plants. More than 75 other families of plants have species that receive varying degrees of feeding injury. Since many ornamentals are favored host plants the association of these ornamentals in a landscape situation makes the Japanese beetle a major pest of golf courses, parks, homes and other well landscaped areas.

Adults feed on the upper surface of the foliage of most plants, consuming soft mesophyll tissues between the veins, leaving a lace-like skeleton. Injured leaves eventually turn brown and die. Trees receiving extensive feeding turn brown and become partially defoliated. When fruit is attacked, the fleshy tissues are eaten. Beetles feed on the maturing silk of corn, so that kernels are malformed through lack of pollination.

Condensed from: Tashiro, 1987 - "Turfgrass Insects of the United States and Canada".
Cornell University Press, Ithaca, NY

Larval Feeding: Grubs feed on the roots of wide variety of plants, including most grasses, ornamental plants and vegetables. Feeding by grubs on the underground stems and roots often passes unnoticed until the plants are badly damaged. Injury to well-kept turfgrass is usually not apparent when there are fewer than 5 grubs per ft² on home lawns (fewer than 10 per ft² on irrigated turf). Most of the severe turfgrass damage shows up in September-October, when third-stage grubs are feeding vigorously just before they go into hibernation and again during April and May. During these two periods most grubs are feeding within the surface 2 inches of soil or the soil-thatch interface. Heavily damaged turf can easily be rolled back or lifted, since all of the fibrous roots have been eaten. Grubs may damage corn, bean, tomato, strawberry and other field and garden plants by feeding on the roots. Nursery stock is often injured when grubs feed on and girdle the main root.

Description of Stages

Adult: Beetles are brilliant metallic green, with coppery brown fore wings that do not entirely cover the abdomen. A row of 5 lateral brushes of white hairs on each side of the abdomen and a pair of these brushes on the bottom surface of the last abdominal segment distinguish this beetle from all others with similar coloration. They begin to emerge in early July and can be found until mid September. After the initial emergence, most beetles leave their tunnels during the morning of clear days for feeding and mating. They return to the soil in the late afternoon or evening to spend the night. Beetles also remain in the soil on cold wet days.

Egg: Eggs measure about 1.5 mm in diameter and are laid in the soil in July and August. Beetles generally lay their eggs in short grasses.

Larva: Larvae begin to hatch in late July and go through three molts before fall. They are less than 1/15 of an inch long when the first hatch and may be as large as 1 inch as third stage larvae. Grubs begin to move downward during the first freezing air temperatures in the fall for hibernation. Grubs move up again during April and May to feed and reach maturity.

Life cycle of Japanese Beetle. Vertebrate Predators: Birds and mammals considerably reduce Japanese beetle grub populations just as they do those of other scarabaeid grubs but may also cause considerable turfgrass damage in the process of digging for their quarry. Starlings, grackles, robins and other birds feed on large numbers of grubs especially during early spring and fall. When crows dig for grubs, they can cause considerable damage to the weakened turf. Mammals attracted to grub-infested turfgrass as a source of food include moles, skunks and raccoons. Biological Control: Milky Spore Disease, caused by the organism Bacillus Popillac, is a bacteria that infects beetles of the scarab family and has become adapted to the Japanese beetle. Commercial formulation of this product can be applied to control Japanese Beetles. Field control in turf is applied at 2 grams of spores deposited at 5-10 foot intervals on turf with high populations of grubs. Currently, there are only two sources of milky disease spore powder, Fairfax Biological Laboratory, Inc. (the product is called Doom), Clinton Corners, New York 12514, and Reuter Laboratories, Gainesville, Virginia 22065. Commercial formulations of this product require about 4 years after application to become effective and can be active against grubs for up to 20 years. Insecticide Control: The major problem caused by adult Japanese beetle in the home setting is the feeding on ornamental plants. Sevin (carbaryl) and Malathion (acephate) are available for over the counter purchase by the general public. Unfortunately, in heavy infestations it may be necessary to treat sensitive plants on a 5-7 day schedule in July and early August. Follow the label instructions for rates as using more than what the label calls for can cause damage to the plants. Always wear long pants, long sleeved shirts, rubber gloves and closed top shoes (rubber boots preferred) when handling any insecticide. If turf damage has occurred in the past, an application of Merit (imadichloprid) can be applied for larval control. If Merit is to be used, it must be applied before August 1 to be effective. If grubs are present and need to be treated, Diazinon granules can be used on home lawns in mid August-mid September or in late April to reduce the population. Commercial landscapers and golf courses may use Dylox, Proxol or Turcam. Trapping: Baited traps are effective tools for detection of Japanese beetle to determine first emergence or presence in an area with a low population. Trapping is not a recommended control method. Traps can only be effective as a control mechanism if they are used in high concentrations. Use of traps will generally attract many more beetles from the surrounding areas. The grass under where the traps are placed and susceptible shrubs and trees near the traps will often be damaged worse than if they were not used. This article was adapted from various references at the MSU Extension office. These include CAT ALERT reports; The Ortho Problem Solver, fourth edition and field expertise. If you have any questions please contact the MSU Extension Office. Bruce MacKellar-District IPM Agent Home Search Feedback Last modified: July 11, 1997