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University of Illinois Extension serving Fulton, Mason, Peoria and Tazewell Counties

Main Office (Tazewell County)
1505 Valle Vista
Pekin, IL 61554
Phone: 309-347-6614
FAX: 309-347-5472
Email:uie-fmpt@illinois.edu
Hours: Monday-Friday 8:00am to 4:30pm (Closed 12 - 1pm)

Branch Office (Fulton County)
15411 N IL 100 Highway
Lewistown, IL 61542
Phone: 309-547-3711
FAX: 309-547-3713
Hours: Monday-Friday 8:00am to 4:30pm (Closed 12 - 1pm)

Branch Office (Mason County)
133 S High, Box 170
Havana, IL 62644
Phone: 309-543-3308
FAX: 309-543-6239
Hours: Monday-Friday 8:00am to 4:30pm (Closed 12 - 1pm)

Branch Office (Peoria County)
4810 North Sheridan
Peoria, IL 61614
Phone: 309-685-3140
FAX: 309-685-3397
Hours: Monday-Friday 8:00am to 4:30pm (Closed 12 - 1pm)

News Release

Management Strategies for Japanese Beetles

June 25, 2012

They're back. Japanese beetles are stripping trees, skeletonizing leaves, and generally decimating plant material often in crackling, buzzing masses. So what strategies are available for managing this irritation of the field, yard, and garden? Those strategies can be divided into three categories - cultural, mechanical, and chemical management.

Cultural control is generally defined as those practices that make the environment less suitable to the outbreak of a pest. While some non-Illinois university resources recommend trap crops, the reliability of trap crops (in relation to this pest) is somewhat questionable. The practice has therefore not typically been recommended for Japanese beetle management in Illinois. Some individuals have also recommended a manipulation of planting dates for certain vegetable crops, targeting those crops to complete the bulk of production or growth before the beetles emerge or after the beetles begin to subside during the late summer. Plant selection can be yet another cultural option. Those familiar with this pest know that Japanese beetles tend to prefer certain plant species over others. Over the long term, individuals can use plants less preferred by this pest. They can also be prepared for injury that will certainly come to favored plant material (Note: Some plants may simply be sacrificed to the beetle – consider the example of linden trees which are almost unsalvageable). Maintaining healthy, vigorous growth is yet another cultural management option. A list of plant material favored by this pest can be found at www.aphis.usda.gov/publications/plant_health/.../JB3-07.indd.pdf

Mechanical control is defined as those practices that exclude or eliminate the pest. The most familiar form of mechanical control for Japanese beetles is hand removal. Hand removal is typically recommended toward dawn or dusk when the beetles are rather docile. Because Japanese beetles release attractants that draw in other beetles, hand removal can be a valuable tool where the pest has just begun to enter new territory. Removal stops the avalanche of beetles as pioneering beetles are submerged in soapy water, but it may not prove useful in those areas typified by exceptionally large infestations. Where elimination does not work, exclusion may. Covers/floating row covers (cloth-like covers of very fine mesh) may keep beetles from reaching foliage and may be useful to area organic gardeners.

Chemical control is defined by the use of pesticides, attractants, repellents, etc. For vegetable growers preferring to not use covers, chemical control may be the only management option available to them. However, growers should remember that not all chemical options provide adult control, that some chemical options make the problem worse, and that all chemical options should be preceded by intense scouting. Grub control options are perhaps the best example of a chemical management option that provides little-to-no adult beetle control. Japanese beetles do persist as a grub during the late summer, fall, winter, and early spring. Grub management (chemical or biological) may eliminate the immature stage of this pest, but because adults are capable of migrating miles the option does not eliminate adult beetle pressure. Adults will simply repopulate those areas devoid of "homegrown" adults. Traps are perhaps the best example of a chemical option that only makes matters worse. Traps only eliminate a small portion of the adults flying into an area, yet they attract many more. Traps therefore draw beetles into an area and create the "population avalanche" described earlier. For this reason, U of I, Iowa State, and Purdue all recommend that individuals not use Japanese beetle traps. Where chemical options are needed, individuals should remember that scouting is necessary. Only that plant material currently suffering injury should be treated for Japanese beetles. Corn fields for instance may often suffer injury to only the outer rows, bean fields may suffer severe injury in only isolated areas falling short of the recommended threshold of 20% defoliation, and gardeners may notice that certain crops are inundated while others are left alone. Preventative measures are not useful (most products degrade within several days of application).

Source: Matt Montgomery, Extension Educator, Local Food Systems and Small Farms, mpmontgo@illinois.edu