Western corn rootworm beetle emerging from the soil.
Western corn rootworm beetle emerging from the soil.

Western corn rootworm beetles were first observed in Tippecanoe County, Indiana, on June 30, captured in pheromone baited sticky cards. The male beetles are generally first to emerge and hang out, feed, and wait for 7-10 days until females begin emerging. Females generally mate upon emergence, then feed and disperse, sometimes over long distances.

After emerging, beetles will begin to feed on corn leaves if pollen is not available. Leaf feeding damage is of no economic importance. However, pollinating plants with high beetle populations could suffer economic losses from the beetles clipping silks prior to the completion of pollination. Pest managers should closely watch their fields for this type of feeding activity when pollination begins. We have not seen high populations in Indiana for at least 4-5 years, but it’s still worth keeping an eye out. Now is the time to look for lodging in fields, especially following rains and wind. Pull, or dig (preferable) some suspicious plants and look for root damage. Rootworm is the only insect to cause root damage at this time of year. Rootworm damage to Bt corn is of special interest and should be noted and reported, as resistance to Bt traited corn has been reported in several states, including IL and MI, in the last several years.

Emergence will continue over several weeks, and adult beetles will survive until late summer. They are consistently attracted to pollen sources throughout their lifespan. Therefore, late-planted fields are particularly susceptible to silk-clipping. Fields with uneven growth and/or replanting may be more vulnerable than most. These delayed areas should be closely watched for silk clipping. For additional information on rootworm beetles and their control, see Extension Publication E-219-W, Corn Insect Control Recommendations - 2014, which can be viewed at http://extension.entm.purdue.edu/publications/E-219.pdf.