Western and northern corn rootworms are serious corn pests in Iowa and the Corn Belt, primarily due to their feeding habits but also because they can overcome nearly all management tactics available to farmers. The larvae tunnel into and consume corn roots, thereby reducing nutrient and water uptake and causing lodging. The adults may also feed on above-ground parts of the plant, including silks and pollen, which may interfere with pollination.
We introduced this trapping network last year for the first time in Iowa, and we will continue this effort in 2021. 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. 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 adults or would like additional information, send an email to email@example.com by June 15, 2021. 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 are 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.
Taking things further
This year, we have partnered with extension and industry personnel in several U.S. states and Canadian provinces to synchronize our data collection efforts and provide a regional perspective on corn rootworm activity. Part of this partnership presents the opportunity for our cooperators to enter their data into an online database called Survey123. This will be an app-based data entry system that cooperators can use for free without creating an account. It will allow cooperators the autonomy of entering their own data, and the data will be used for live mapping of reports that will be publicly available on a webpage. We will make sure your privacy is protected. More information on Survey123 will be provided via email in late June, and you can opt-in at that time.
Cooperators will not be obligated to use the application to enter data; people will still be able to email their trap captures to firstname.lastname@example.org, which will be kept for our use only.
How can this help farmers?
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. 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.
It should be noted that four traps per field is a small sample and will not completely represent adult activity in that field. Implementing multiple transects is ideal for understanding adult density, so use caution when making management decisions based on a single transect.