Japanese beetles

First reported in North America in 1916, the Japanese beetle now occurs in most of the eastern United States. About 1/2 inch long, Japanese beetles are a shiny, metallic green with coppery brown wing covers that extend almost to the tip of the abdomen. Small tufts of white hairs occur at the tip of the abdomen and along each side. Eggs are translucent white to cream and elliptical and about 1/16 inch in diameter when first laid. In a few days, the egg becomes more spherical and doubles in size. Grubs are white, slightly curled and have yellow-brown heads. Grubs are about 1 inch long when mature. Unlike other grubs found in turf, it has two rows of spines which form a “V” on the underside of the last abdominal segment. The pupa is approximately 1/2 inch long and 1/4 inch wide, and it gradually turns light brown and then develops a metallic green cast.

Biology
Adult Japanese beetles sometimes emerge as early as mid May in eastern North Carolina. Peak emergence occurs mid-late June in most areas and lasts a few weeks. The beetles attack the foliage, flowers and fruit of many plants. Japanese beetles feed on over 275 different kinds of shade and fruit trees, shrubs, flowers, small fruits, garden crops, and weeds. Some of their favorites are roses, crape myrtle, linden, grapes, as well as ornamental and other fruit trees. They typically feed on the upper leaf surface eating tissue between leaf veins giving leaves a lacy appearance. Beetles will generally consume entire petals of roses and other flowers.

Japanese beetles aggregate in response to odor released by damaged plants and a pheromone released by female beetles. This aggregation and mass feeding can result in severe defoliation of plants.

Soon after emerging, female beetles burrow 2 to 3 inches into damp soil and deposit 40 to 60 eggs in small batches. During dry periods, adults may be more attracted to low lying and irrigated areas to lay eggs where soil moisture is higher. In extremely dry weather, many eggs and larvae perish. In warm, wet summers, eggs hatch in about 2 weeks. The newly emerged larvae feed until cold weather forces them into hibernation. One generation occurs each year.

The beetle grubs are only occasional pests of the roots of grasses and shrubs. Japanese beetle grubs occur in lawns, golf courses, pastures and even wooded areas. They burrow through the soil feeding on roots. Areas of dead grass may appear when large numbers of grubs are present especially during dry spells in September or early October. The grubs overwinter in cells about 6 inches deep. In spring, they move almost to ground level, where they complete feeding and then pupate. Japanese beetle grubs rarely do enough damage in a home lawn to warrent treatment. The threshold is approximately 12+ grubs per square foot.

Scouting/Monitoring
Japanese beetles adults generally become active in late May or early June in North Carolina depending on location and weather. Peak abundance and feeding occurs in late June or early July. Monitoring can easily be done with commercially available bag-type Japanese beetle traps. You can also monitor highly attractive plant species such as roses for the appearance of beetles. Traps are commercially available. The traps are much more effective in attracting Japanese beetles than in trapping them. Consequently, traps should be placed as far away from the plants to be protected as possible. If traps are used, place far away from susceptible plants. Traps, alone, are not likely to give satisfactory protection to plants being eaten by adult Japanese beetles and pesticides may be required, anyway.

Decision Making
Deciding when and how to manage Japanese beetles will depend on beetle activity in your area and the value and vulnerability of plants on your property. A number of plant species and varieties are unlikely to be attacked or heavily damaged by Japanese beetles and thus would not require intervention. However, highly susceptible plant species such as roses could suffer severe damage and warrant some sort of intervention.

Commercial nursery and landscape operators will have less tolerance for damage in order to keep plants salable and presentable in the landscape. Commercial operators should reference Insect Note xx “Management of Adult Japanese Beetles for Commercial Nursery and Landscape Operations” for more information.

Intervention/Control
Flowers and ornamental plants can be protected by dusting or spraying foliage with pesticide. However, there are a number of options for reducing damage to landscape plants that do not rely entirely on pesticide applications. Many plants are not significantly bothered by Japanese beetles. There are also varieties of their favorites that are less preferred than others. For a list of susceptibility of certain woody ornamentals to Japanese beetle damage see the Mississippi State study.

Homeowners can take advantage of the beetles’ aggregation behavior by shaking plants to dislodge beetles each morning. Without beetles already on a plant, it is less likely that beetles will aggregate there later in the day. Picking beetles off by hand will also reduce the accumulation of beetles that results in severe damage. They can be easily knocked into a widemouth jar of soapy water. In some settings, flowers or plants can be protected with cheesecloth or other fine mesh.

If insecticides are desired to protect plants in the landscape, there are a number of products available. For home use, carbaryl (Sevin), malathion, imidacloprid (Merit) are good choices. Many of the newer lawn and garden multi-insect products containing one of the pyrethrins are also effective. Pyrethrin containing chemicals are slightly more persistant. Sevin will protect foliage for about five days, weather permitting, so it would have to be reapplied. Pyrethroid based products may give up to two weeks of foliar protection per application. Spinosad and Neem based products are less effective, but are preferred by some gardeners seeking “softer” chemicals. Homemade concoctions and blended beetle cocktail repellants are slightly effective at best, and may need reapplication every one or two days.

Japanese beetle traps may catch up to 75% of the beetles that approach them. However, they are not control devices. Traps may lower beetle populations slightly, but only if placed throughout an entire neighborhood at very high density. This will not be enough to significantly reduce damage on your prized garden foliage. The trapped beetles must be emptied from the traps every one to two days to prevent them from rotting and releasing ammonia which is repellant to other Japanese beetles. The traps are much more effective in attracting Japanese beetles than in trapping them. Consequently, traps should be placed as far away from the plants to be protected as possible. If traps are used, place far away from susceptible plants. Traps, alone, are not likely to give satisfactory protection to plants being eaten by adult Japanese beetles and pesticides may be required, anyway.

For commercial operations, a number of systemic products such as imidacloprid are effective and protect trees for longer periods of time. Commercial operators should reference Insect Note 147 “Management of Adult Japanese Beetles for Commercial Nursery and Landscape Operations” for more information.

Grub control
Commercial soil treatment preparations of the Bacillus popilliae (milky spore disease) offer very little benefit. These spores infect and kill only Japanese beetle grubs. The spores are released into the soil and infect new grubs as they come in contact with the bacterial spores. Milky spore preparations can be applied from July until the first hard freeze to areas of turf grass that are mowed to 2 to 3 inches tall. These areas are preferred egg laying sites for adults and here, during the warm months, grubs feed close to the soil surface. Results of milky spore have been disappointing, however, and generally do not justify the expenditure. Milky spore treatment also provides little relief for the homeowner from the onslaught of foliage feeding by the highly mobile adults which fly into the area. Japanese beetle grub populations rarely reach economic threshold levels as turf pests in home lawns. A general threshold is 10 grubs per square foot (fewer on commercial turf) before turf damage becomes an issue. In addition, only small areas of the turf may be infested, so do not assume the entire area is infested. Heterorhabditis species of nematodes may be a more viable non-chemical alternative for turf protection, but application directions must be carefully followed. Remember, home lawns rarely need Japanese beetle grub intervention.

Soil insecticides for grub control are available, but rarely needed or justified for home owners. Imidacloprid-based insecticide applications any time from late spring through summer are fairly effective. The residual life of the soil applied chemicals varies, so follow the label instructions. Killing all grubs in a lawn will not protect your shrubs from Japanese beetle adult feeding so grub insecticides for adult beetle control are an unnecessary use of pesticide.

No matter which product or approach is selected, be sure to follow label directions. Recommendations for insecticides approved for control of these insects in home lawns can be found under the “White Grubs” listing in the Insect Control in Home Lawns section of the NC Agricultural Chemicals Manual. Recommendations for insecticides approved for use on sod farms, golf courses or other commercial sites can be found in the Commercial Turf Insect Control section of the NC Agricultural Chemicals Manual.

Useful References

• APHIS Japanese Beetle Homeowners Manual
• Minnesota note http://www.extension.umn.edu/distribution/horticulture/DG7664.html
• Relative Susceptibility of Woody Landscape Plants to Japanese Beetle. David Held, Mississippi State University. Journal of Arboriculture 30(6) November 2004. http://www.treelink.org/joa/2004/nov/held11-04.pdf
• Redmond, C. T. and D. A. Potter. 1995. Lack of efficacy of in vivo- and putatively in vitro-produced Bacillus popilliae against field populations of Japanese beetle grubs in Kentucky. J. Econ. Entomol. 88: 846-854.
• Klein, M.G. 1992. Chapter 4. Use of Bacillus popilliae in Japanese Beetle Control, pp 179-190. In: Use of Pathogens in Scarab Pest Management. T.R. Glare & T.A. Jackson, eds., Intercept Ltd., Andover, England. 298pp.
• White Grubs in Turf. NC Note http://www.ces.ncsu.edu/depts/ent/notes/O&T/lawn/note67/note67.html

Recommendations of specific chemicals are based upon information on the manufacturer’s label and performance in a limited number of trials. Because environmental conditions and methods of application by growers may vary widely, performance of the chemical will not always conform to the safety and pest control standards indicated by experimental data.

Recommendations for the use of chemicals are included in this publication as a convenience to the reader. The use of brand names and any mention or listing of commercial products or services in this publication does not imply endorsement by the North Carolina Cooperative Extension Service nor discrimination against similar products or services not mentioned. Individuals who use chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain current information about usage and examine a current product label before applying any chemical.

Other Resources

• Back to Insect Notes
• Horticulture Information Leaflets(HILs)
• Plant Disease Notes
• North Carolina Agricultural Chemicals Manual
• North Carolina Cooperative Extension Service

For assistance with a specific problem, contact your local North Carolina Cooperative Extension Service.

Article written by Patsy McNatt, Extension Master Gardener Volunteer.