A survey of corn farmers in Iowa shows which insect pests are of most concern and that most are not seeing failures in management methods such as Bt crops. But they do look to IPM and extension agents for guidance in managing insecticide resistance. (Photo by hj_west via Flickr, CC BY-SA 2.0)

By Ashley Dean and Erin Hodgson, Ph.D.

Erin Hodgson, Ph.D.

Ashley Dean

Corn is the number one crop in Iowa in terms of acreage planted and production value. Profitable corn production relies on numerous factors, including effective pest management strategies. Corn is attractive to many species of insect pests, but the importance of a specific species varies spatially and temporally and is affected by decisions farmers make. For these reasons, it is important for extension personnel to understand farmers’ perceptions and concerns to provide relevant programming.

Members of the Iowa State University Agriculture and Natural Resources Crops Team surveyed farmers during winter extension programs in 2019-2020. The survey, delivered as a paper survey to most participants, asked farmers about their insect pest of greatest concern, whether they have concerns about the performance of management tactics (Bt hybrids and insecticides), and whether they felt confident in developing a resistance management plan or discussing plans with their advisor (typically an agricultural retailer or seed dealer). Findings from the survey were shared in a report published in July in the Journal of Integrated Pest Management.

Major Insect Pests of Concern

We anticipated farmers would be most concerned about western corn rootworm (Diabrotica virgifera virgifera), considering the potential to cause significant yield loss and that some populations have overcome all Bt traits. However, at the statewide level, the majority of farmers were concerned about northern corn rootworm (Diabrotica barberi). At this time, northern corn rootworm is not resistant to Bt traits in Iowa.

We noticed regional trends in responses that were unexpected (see map). In general, northeast and northcentral Iowa chose northern corn rootworm as the major pest of concern, northwest and west central Iowa chose western corn rootworm, southern Iowa chose corn earworm (Helicoverpa zea), and central/eastern Iowa chose European corn borer (Ostrinia nubilalis).

A survey of Iowa corn growers asked about their biggest pest issue of concern; results here are shown by county. The number in parentheses represents the total number of respondents in each county. Where counties have multiple colors, an equal number of respondents indicated these pests were the biggest concern.

Concerns About Performance of Management Tactics

Overall, the majority of farmers were not concerned about the performance of management tactics we inquired about (above-ground Bt, below-ground Bt, insecticidal seed treatments, soil-applied insecticides, or foliar-applied insecticides). Across the entire state, farmers were most concerned about the performance of below-ground Bt and least concerned about above-ground Bt. Only in the northeast crop reporting district of Iowa were the majority of farmers concerned about the performance of below-ground Bt. This makes sense considering Bt-resistant western corn rootworm were first identified in Iowa in the northeast part of the state.

Although most farmers indicated they were not experiencing Bt trait failures for corn rootworm (below-ground Bt), about 24 percent of farmers indicated they did not know whether they had failures. This could represent a knowledge gap for identifying trait failures in the field that could be included in future extension programs. Timely identification of trait failures would undoubtedly be valuable to the farmer.

Erin Hodgson, Ph.D., professor and extension entomologist at Iowa State University, examines a corn stalk damaged by northern or western corn rootworms. The two species rank among the insect pests of highest concern among corn farmers in Iowa. (Photo courtesy of Erin Hodgson, Ph.D.)

In her role as an education extension specialist at Iowa State University, Ashley Dean (left) advises farmers and the public at large on integrated pest management issues in field crops such as corn. (Photo courtesy of Erin Hodgson, Ph.D.)

Confidence in Developing and Discussing Resistance Management Plans

It is our understanding that most farmers make management decisions with the help of advisors (e.g., consultants, agronomists, and input suppliers). Our survey indicates that farmers feel somewhat confident in developing a resistance management plan for their farm, and they generally feel more confident in discussing these plans with their advisors. If farmers feel confident in these interactions, it may be critical to focus extension efforts on training advisors and increasing their confidence in making recommendations.

Conclusions

Based on the results of this survey, future extension efforts should focus on:

• region-specific pest topics
• how to identify pests and control failures
• prioritizing proactive efforts for resistance management
• helping farmers and advisors identify effective management strategies
• increasing confidence in developing resistance management plans (farmers and advisors).

Ashley Dean is an education extension specialist at Iowa State University in Ames, Iowa. Twitter: @ashleyn_dean. Email: adean@iastate.edu. Erin Hodgson, Ph.D., is a professor and extension entomologist at ISU. Twitter: @erinwhodgson. Email: ewh@iastate.edu.