Corn Management Scenarios for Earworm

Corn earworm is a tough pest

Corn earworm (CEW), Helicoverpa zea, is a migratory pest in Iowa. Multiple arrivals and subsequent generations once in Iowa result in continuous infestations. CEW has a wide host range, but the greatest economic concern in Iowa is in sweet corn. Farmers plant many successions for continuous production, and consumers demand caterpillar-free ears (ick!) and non-GMO hybrids. These factors create a complicated pest management system that results in foliar insecticides being applied every 3-5 days during silking to protect ears. 

In the U.S., research has demonstrated poor efficacy of some insecticides and transgenic traits for CEW in several crops, including sweet corn. The threat of resistance comes from many angles:

1. target site mutations resulting in pyrethroid (Group 3A) resistance from repeated exposures¹;
2. resistance to Cry toxins used in Bt hybrids²; and/or
3. CEW moths arriving in Iowa with metabolic resistance to Group 3A from interbreeding with Helicoverpa armigera³.

A new tool for farmers

In 2024 and 2025, commercial farmers saw extensive injury to sweet corn ears. In 2024, two Iowa fields had 57% and 100% Group 3A-resistant CEW⁴. Assays from 2025 collections are pending. These farms gave away bonus ears to compensate for high infestations. Resistance issues prompt questions about profitable and sustainable solutions to manage CEW. We developed a dynamic tool to help farmers implement integrated pest management (IPM) practices and use decision-making tools to improve their return on investment (ROI).

In order to generate a realistic budget and IPM plan for Iowa farmers, we collected the following information:

1. yield/revenue estimates from farmers;
2. chemical/seed costs from cooperatives;
3. custom spraying/scouting costs; and
4. moth trapping supply costs.

Download the Corn Earworm Budget Tool to review the specifics of the scenarios presented. You can input custom values to calculate your ROI!

Corn Earworm Budget Tool (xlsx)

Corn earworm management scenarios

To demonstrate how this tool can be used to compare management strategies for corn earworm, we analyzed three scenarios: a traditional approach, a modified approach to compensate for Group 3A resistance, and an IPM approach.

Variable costs in our analysis included the inputs that may change for corn earworm management. We assume all other sweet corn production costs would stay the same, regardless of the corn earworm management scenario. Variable costs for corn earworm include:

• sweet corn hybrids: conventional or Bt;
• insecticides: number of applications, group number(s) selected; and
• moth traps, lures, and labor.

These variables can be modified to fit individual operations using the tool.   

Every economic analysis must make some assumptions since every operation is unique. Our assumptions for the analysis include:

• 22,000 seeds per acre; every plant survives and produces one ear;
• fifty percent of CEWs are resistant to Group 3A;
• farmers give bonus ears for the price of  a dozen when CEW injury is high; and
• insecticides that are not Group 3A are effective against CEW.

We used the threshold-based trapping guidelines established in 1996⁵ (Table 1) to determine the number of insecticide applications using an IPM approach.

Three management scenarios:

Scenario 1: Traditional approach

This scenario mimics what has been the status quo for a sweet corn planting.

• 7 insecticide applications using only Group 3A; 
• conventional sweet corn hybrid; and
• no moth trapping. 

ROI estimate = $30.90 per $1 invested in corn earworm management.

Scenario 2: Alternating insecticide groups

This scenario is similar to what many sweet corn farmers have had to do since 2024.

• 7 insecticide applications, alternating Group 3A with another group; 
• conventional sweet corn hybrid; and 
• no moth trapping. 

ROI estimate = $27.90 per $1 invested in corn earworm management.

Scenario 3: IPM approach

This scenario outlines what the ROI could be if a sweet corn farmer incorporated moth trapping and an IPM approach using Table 1.

• 4 insecticide applications, alternating two non-Group 3A insecticides; 
• conventional sweet corn hybrid; and 
• threshold-based sprays with moth trapping. 

ROI estimate = $31.80 per $1 invested in corn earworm management. This calculation includes the up-front cost of purchasing a Heliothis trap, which likely has a lifespan of at least 5 years. If the trap costs are spread out over 5 years, the ROI jumps to $34.90.

Corn earworm IPM recommendations

Pyrethroid resistance is becoming a more prevalent issue in Iowa for a number of pests. Our recommendations for CEW management in sweet corn are to:

1. monitor moth flights with phermone traps;
2. use threshold-based guidelines for timing insecticide applications;
3. alternate non-Group 3A insecticides; and
4. use Bt hybrids, if they are acceptable to consumers, for late-season plantings.

CEW moth capture data from 2016-2024 in central Iowa (see graph) suggests fields silking during mid-August through September are at the highest risk. Using Bt hybrids for these successions would greatly reduce reliance on insecticides.

The budget tool is a work in progress, and we continue to improve the economic model to account for more complex and dynamic real-world scenarios. Improved accuracy will come from annual updates for input costs and market conditions; variable moth flights; and Group 3A and Bt resistance statuses.

References Cited: ¹Olmstead et al. 2016, Biology, Ecology, and Evolving Management of Helicoverpa zea (Lepidoptera: Noctuidae) in Sweet Corn in the United States; ²Dively et al. 2023, Extended Sentinel Monitoring of Helicoverpa zea Resistance to Cry and Vip3Aa Toxins in Bt Sweet Corn: Assessing Changes in Phenotypic and Allele Frequencies of Resistance; ³Nufer et al. 2024, Anatomy of a pest control failure: introgression of cytochrome P450 337B3 alleles from invasive old-world bollworm into native corn earworm (Lepidoptera: Noctuidae); ⁴Hodgson and Dean. 2024, Consider Your Corn Earworm Management Options For Sweet Corn; and ⁵Dively. 1996. Northeast sweet corn action thresholds and decision-making guide (PDF).
 

Acknowledgements: USDA-ARS Lab in Ames for historical corn earworm data (Craig Abel) and resistance monitoring efforts (Brad Coates); agriculture industry contacts for providing pricing information; sweet corn farmers for sharing economic information; and Ag Decision Maker (Ann Johanns) for the Excel template and hosting the tool. Photos by Erin Hodgson and Ashley Dean.