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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 9:00am 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

What About Japanese Beetles in Beans?

June 25, 2012

Producers in areas annually plagued by the Japanese beetle are familiar with scouting recommendations for this pest in corn. Producers are supposed to scout deep into their fields, carefully shucking ears to see if the majority of silks fall or remain attached (falling silks are an indication of fertilized ovules/ established kernels). Noting beetle populations in combination with this estimate of "fertilization progress" gives producers a reasonable idea of field susceptibility/yield loss potential from the Japanese beetle. In past years, many of these silk-clipping pests have only "done their dastardly deed" after fertilization is complete in most of the field thus negating any benefit from an insecticide application. However, many wonder about the Japanese beetle threshold for bean fields because the pest has emerged while silks are largely absent. Can Japanese beetles be a "yield-reducing" pest in soybean fields?

Japanese beetles, transplanted in our country from the main islands of Japan in the early twentieth century, feed on a wide variety of plant material and many different crops. They overwinter as grubs, deep in the soil profile, which move back into the root zone to feed and complete development the following spring. Pupating in mid-to-late May, the insects emerge as adult beetles starting in June. Adults, shiny metallic beetles with bronze wing covers and tufts of white hair on either side of the abdomen, mate and lay eggs through September.

Japanese beetles cause damage, which resembles a network of small holes while feeding on soybean leaves. They may also feed on flowers. However, as with corn, leaf damage is rarely of economic significance. While a possible yield reducer in soybean fields, Japanese beetles are only deemed of economic significance when twenty percent defoliation occurs between bloom and pod fill (that is 20 percent removal of the entire leaf area from a field not from individual plants). Populations rarely reach a level capable of inflicting such injury in the field. Such injury is occasionally encountered and occasionally occurs when Japanese beetles feed alongside other pests in the field.

The average defoliation in the field can be estimated by harvesting a few plants in several, evenly-spaced locations in a line running through the field. Plants can be grouped together based upon defoliation with a reasonable estimate of defoliation made from such a survey. If the total leaf area removed does not equal 20 percent, spraying the entire field will likely not yield a return on investment.

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