Western and northern corn rootworms are serious corn pests in Iowa and the Corn Belt, reportedly responsible for over 1 billion dollars in yield loss and control costs annually in the United States. The larvae tunnel into and consume corn roots, which can reduce nutrient and water uptake (Figure 1). Extensive feeding can completely eliminate roots and cause lodging. One node (about 10 roots) of injury equates to approximately 15% yield loss under normal field conditions and even more when plants are drought-stressed.
Although larvae are the most damaging life stage, adult western and northern corn rootworms can feed on corn leaves, silks, pollen, and kernels (Figure 2). Feeding on pollen and clipping silks can interfere with pollination, especially if silking is delayed.
High adult activity may be concerning and indicate issues for the following growing season. The action threshold for adult corn rootworm is two beetles per sticky trap per day, regardless of species. If this action threshold is met, strongly consider crop rotation. If planting corn the following growing season, make sure to use a pyramided Bt trait with Cry34/35Ab1 or a soil-applied insecticide on non-rootworm Bt hybrids.
This year, we are interested in monitoring for corn rootworm adults throughout Iowa to get a sense of how populations vary across the state. We are also interested in species composition (ratio of westerns to northerns). Since this is a huge undertaking, we are asking for volunteers to monitor sticky traps this summer. Aside from providing data to us, we hope these traps can provide the volunteer valuable insight for their field or a client’s field and that this information can be used by farmers, crop consultants, and agronomists who make management decisions. We will compile data and report findings later this summer.
Want to be a volunteer trapper?
If you are interested in volunteering to set up and monitor traps for corn rootworm or would like additional information, send an email to firstname.lastname@example.org by June 15, 2020. Please include your contact information and mailing address in the email. As part of the Iowa corn rootworm monitoring network, we will provide enough traps for each cooperator to monitor one transect (four traps) for four weeks. If a cooperator is interested in continuing to monitor after the four weeks is up or wants to place more traps in their field, additional traps may be purchased from several retailers. We purchased unbaited Trécé Pherocon AM traps from Great Lakes IPM for this project.
Traps and a protocol will be mailed to you in late June. It can take over a month for the emergence of adult corn rootworms to be complete, depending on degree day accumulation, but we will aim to capture peak emergence through our network. Trapping will likely begin during the third week of July.