An interstate program to monitor corn rootworm populations in the Corn Belt shows adult beetles became more prevalent between 2016 and 2017. Hot spots for high beetle numbers centered in northern Iowa, with average field observations that exceeded recommended population thresholds.
CRW threatens an estimated 50 million acres of U.S. cornfields, costing producers about $200 million annually in preventive measures and $800 million in yield loss. Research shows every root node nibbled by larvae results in a yield loss of about 15%. In addition, weakened roots can impede harvesting, further reducing grain yield by 15% to 34%.
The 2017 CRW monitoring project led by Sean Evans, corn systems technology development manager at Monsanto, included more than 1,200 fields. In 2016, over 300 fields were monitored. Although the number of monitored locations is greater between 2016 and 2017, the resulting data maps show similar regions of constant high risk.
Counties with high corn rootworm risk
Of the Iowa fields included in the monitoring, Delaware and Sioux counties had the highest number of acres with significant corn rootworm risk, meeting the threshold for high populations of adult beetles. Additional Iowa counties with multiple fields meeting the threshold for a corn rootworm hot spot included Buchanan, Grant, Hamilton, Cedar, Clayton, Hancock, Humboldt, Muscatine and Webster.
On the positive side, more than 20 Iowa counties in the study had significant low risk of rootworm, including Jasper, Poweshiek and Cass. Considering the infestation map generated with the data, farmers should be aware that field sample sizes were variable, and some counties that appear to have little risk may not have been monitored for the research project.
“If I’m farming in one of the hot spots, I don’t need a map to tell me,” Evans says. “What the map does tell me is in the overall landscape, corn rootworm is higher. If I have a field that didn’t quite meet expectations in 2017, maybe the yield wasn’t quite where it should be, or there were standability issues [where] rootworm might be the cause.”
Gauge rootworm risk correctly
Hot spot areas are most prominent in northwest Illinois, northern Iowa, northeast Nebraska and northeast Colorado. Those areas have a long history of continuous corn planting to accommodate livestock feeding or high-production, irrigated fields.
When considering inputs, farmers need to evaluate the best return on investment for CRW control while considering the risks. If you don’t gauge corn rootworm risk correctly, damage from the insect can result in a significant loss in yield and income.
“The potential for corn rootworm is always there and needs to be watched for and managed,” says Randy Francois, who farms at Winthrop in northeast Iowa. He manages 350 acres and helps his family farm a diversified grain and livestock operation. Demand for feed requires them to keep 80% of acres in continuous corn.
“We started planting SmartStax products to stay ahead of corn rootworm,” Francois says. “SmartStax has performed very well for us. There is no yield drag, and it provides peace of mind.”
Successfully managing CRW
Managing CRW successfully is possible with integrated pest management strategies to control what USDA calls “the billion-dollar pest.” Farmers should consider all available control options to break the CRW life cycle and manage each field according to risk for infestation, Evans says. Fields at high risk for CRW include continuous corn and adjacent fields, and fields planted in 2017 with a later-maturing corn hybrid.
“The downside of underestimating risk of rootworm damage can be more costly than a control option that falls short, for return on investment,” Evans adds. “Considering average values, current input costs and commodity prices, rootworm only needs to infest one out of four or five seasons to justify the cost of a stacked trait like dual mode-of-action SmartStax RIB Complete corn blend products.”
BMPs provide practical solutions to reduce CRW populations, limit rootworm damage and enable insect resistance management. Farmers are advised to select and incorporate the BMP that best compensates for field history, whether it is rotating to a non-host crop, applying insecticides when necessary or protecting crops by planting dual mode-of-action SmartStax RIB Complete corn. For more information, visit genuity.com/BMPs or consult a seed representative.
Issues with continuous corn
Most issues with corn rootworm begin in continuous cornfields in the fourth year. Farmers moving fields from corn on corn into rotation should start small, but plan for a rotation crop every three to four years.
“One year of soybeans is as good for controlling corn rootworm as five years of continuous soybeans,” Evans says. “Corn rootworm larvae that hatch in soybean fields do not survive, and thus the life cycle of the insect is broken on that field.”
While rotation is an effective CRW control tool most of the time, two CRW species have adapted to that management practice. The northern CRW can lay dormant for a season or more, and some western CRW adults lay eggs in soybean fields. Even with these adaptations, adoption of BMPs for corn rootworm has played a role in keeping the insect in check since 2014. Also, recent history helped to stymy the prolific corn pest.
Less continuous corn, more tech
“Since 2012, corn rootworm management has changed, and acres in continuous corn have gone down,” Evans says. “SmartStax Trait Technology also impacts rootworm pressure. But a key factor has been weather.”
2012 was a peak year for corn rootworm populations, followed by heavy infestations in 2013. The extremely cold winter of 2013-14 impacted CRW eggs, resulting in low survival rates. To further devastate CRW populations, larvae hatching in spring 2014 and 2015 emerged in a saturated environment, and survival rates dipped significantly. In 2016 and 2017, the weather conditions were more favorable to corn rootworm larvae.
The industry-wide monitoring program was supported by eight ag business organizations with contributors posting sticky traps to capture and report beetle numbers. Traps were replaced weekly for three to eight cycles, with beetle captures expressed as average beetles per trap per day between mid-July through early August.
Data was collected in Colorado, Iowa, Illinois, Indiana, Kansas, Minnesota, Michigan, North Dakota, Nebraska, Ohio, South Dakota and Wisconsin. The monitoring area started on the eastern side in Indiana and continued in a horseshoe shape through the Corn Belt to Colorado. Organizations involved with the monitoring program included Monsanto, Wyffels Hybrids, AgReliant Genetics, Iowa Soybean Association, Latham High-Tech Seeds, Champion Seed, Kitchen Seed Company and Axis Advance.
CRW project results
The map developed from the Corn Rootworm Monitoring project provides a high-level guide of where the monitoring team saw CRW pressure in 2017 and helps to identify annual population hot spots for rootworm. Red areas indicate captures of greater than five beetles per trap per day.
The map resulting from the Corn Rootworm Monitoring collaboration led by Monsanto shows strictly cornfields. The map is a representation of average-value sampled areas only and based on an interpolation of point data. The intention of the map is to serve solely as a high-level guide of where the monitoring team saw CRW pressure in 2017. The data and map should not be used as a prediction or characterization of where CRW will be in the future.