May 7, 2010

Last week I was asked, “Will a sugarbeet field that was wireworm-infested last year spell trouble for dry beans if I plant them into that same field this year?” The answer is, probably not. Here's why.

Figure 1.  Click beetle larvae are better known as wireworms.  (Photo by Jim Kalisch, UNL)

Although there are over 700 species of wireworms in the United States and Canada, very few species cause damage to crops. (Most pest species are in the genera Ctenicera and Limonius.) Wireworms (Figure 1) are typically unevenly distributed throughout a field; therefore, crop damage is recognized by distinct areas of reduced stand. Activities that put a field at higher risk for wireworm damage are crop rotation with cereals and poor control of weedy grasses. These activities can contribute to increased damage potential because female click beetles are attracted to grasses to lay eggs.

The pest wireworm species found in Nebraska take 2-5 years to develop to adults (the adults are called click beetles). These multi-year life cycles can cause their numbers to increase greatly at some locations.

In Nebraska, wireworms can feed on the seeds, roots, or hypocotyls of many spring-planted crops, including, in rare situations, dry beans. However, dry beans emerge quickly after planting in the warm May or June soils of western Nebraska. This fast growth allows the beans to outgrow the potential for wireworm damage. Additionally, wireworms will move deeper than 6 inches to avoid the warm soil temperatures in early summer, further reducing potential damage. However, if cool soil temperatures persist, these insects could cause damage in dry beans.

Management

Although rarely needed in dry beans, some chemical controls are available as seed treatments or planting-time applications (see Table 1). It may be too late to purchase treated seed for this year; however, T-band or in-furrow applications remain an option.

To help quantify the level of risk in a field, Iowa State University developed a simple and inexpensive scouting procedure using bait traps (see Trap Wireworms Before Planting Corn). While this procedure has not been tested for wireworms in western Nebraska, it may be sufficient to estimate risk.

Jeff Bradshaw
Extension Entomologist, Panhandle REC, Scottsbluff

Table 1. Insecticides labeled for planting-time use in dry beans against wireworms