Managing western bean cutworm: An impending threat to organic field corn, sweet corn, and dry bean growers

View the project final report

Commodities

• Agronomic: corn
• Vegetables: beans, sweet corn

Practices

• Pest Management: biological control

Western bean cutworm (WBC) is an emerging pest of sweet corn, field corn, and dry beans in the Northeast, moving from its historic range in the western Great Plains through the Midwest and reaching New York and Pennsylvania in 2010. WBC larvae infest corn ears, rendering sweet corn unmarketable and reducing yield and quality in field corn. In dry beans, WBC can reduce yield and quality by feeding on developing beans. Economic damage was seen in sweet corn and dry beans in NY in 2015. Organic growers of these crops do not have proven methods for controlling WBC. We propose to test releases of Trichogramma ostriniae (Tost), a commercially available parasitic wasp that is currently being used in organic sweet corn and peppers for European corn borer (ECB) control. This past season, on two farms releasing wasps in sweet corn for ECB control, we saw extensive damage from WBC, indicating that the release numbers that are effective against ECB are not sufficient for WBC. We will test releases of higher levels of wasps to obtain preliminary data on the potential for Tost to control WBC. Tost has been shown to parasitize WBC eggs in the lab and in field cage studies, but has not been tested against WCB in the field. If we have success with this project, we will use the data collected to seek additional funding to explore the most effective and economical methods for using Tost for WBC management.

We want to know if releases of Trichogramma ostriniae (Tost), a tiny parasitic wasp that attacks moth eggs, will provide control of western bean cutworm (WBC) in sweet corn, field corn, and dry beans. Releases of Tost are currently being used by organic and no-spray sweet corn and pepper growers for European corn borer management throughout the Northeast. Surveys on two farms releasing wasps against European corn borer found significant WBC damage, indicating that the release rates used for ECB are not sufficient to control WBC. We propose to test releases of higher rates (100,000 Tost per acre), to determine to what extent they will parasitize WBC eggs in the field, preventing them from hatching into the damaging larval stage. We will target our releases to cover the roughly three-week peak flight period in late July-early August, focusing on corn fields in the late whorl through green silk stage most attractive to egg laying moths. We have recruited as collaborators organic corn and dry bean growers from western and northern NY, areas that have the highest trap catches and greatest potential for economic losses.

We have identified four collaborating farmers, each located in an area of high WBC pheromone trap catches in 2015. Thorpe’s Organic Family Farm grows both sweet and field corn, and we’ll release Tost in up to three fields in each crop. Tom and Delta Keeney’s Windswept Meadows Farm (where they grow unsprayed sweet corn) is six miles from Jim and Cindy Worden’s organic field corn. We will release in all susceptible plantings of the Keeney’s sweet corn and up to three of the Worden’s field corn. R.L Jeffres Farm grows organic dry beans and we will release in three fields near locations with high 2015 pheromone trap trap catches.

We will deploy WBC pheromone traps at each of the study locations in early July and check traps weekly. At the same time we will track the growth stages of sweet and field corn to identify plantings or fields with a high probability of being in the attractive late whorl to green silk stage during the peak moth flight. Trichogramma ostriniae wasps will be reared on Ephestia kuehniella eggs in the Hoffmann lab using well-established methods developed over the last two decades, and placed in release packaging to protect them from predaceous insects in the field. We will release at a rate of 100,000 per acre in all three crops. Release packages will be evenly spaced in release areas of fields starting the week after first trap catch and weekly releases will continue through one week after peak flight for a total of 3-4 weekly releases.

 In sweet corn: Releases will be in fields in the late whorl through tassel emergence stage once WBC activity has been detected. We will evaluate the effectiveness of the releases by collecting WBC egg masses, bringing them back to the lab, and determining the proportion of WBC eggs exhibiting parasitism. To prevent economic losses for our collaborating growers we will also scout fields at tassel emergence and growers will have the option to apply an insecticide if the field is over the established 15% infestation threshold. If fields are not sprayed we will also evaluate release effectiveness by examining 200 randomly selected ears at harvest to determine infestation levels and compare with infestation levels in nearby untreated field corn.

In field corn: Releases will be in fields in the most attractive stage for egg-laying during the WBC flight. Because field corn is often planted in one short window, we may not have tassel emergence to green silk stage corn available, depending on the season. One corner or end of the field (approximately ¼ of the field) will be designated for releases and the other corner or end of the field will be designated as an untreated control. To evaluate the effectiveness of the releases, we will examine 200 randomly selected ears each from the release and untreated control area to determine infestation levels.

In dry beans: Releases will be in fields close to locations with high 2015 trap catches. One end or corner of the field (approximately ¼ of the field) will be designated as a release area and the other end or corner of the field as an untreated control. At least a half-acre in each area will be flagged off and not receive insecticide applications. To evaluate effectiveness, all pods on 10 plants at each of randomly 10 locations in the unsprayed areas of both release and no-release areas of the fields will be examined for WBC feeding damage.

WBC infestation levels in unsprayed sections of release and non-release areas of field corn and dry bean fields will be compared using T-tests, with a null hypothesis of no difference between release and non-release areas. Statistical analysis of results from sweet corn will not be possible because of the lack of untreated control, but we may be able to make inferences by comparing infestation levels in nearby field corn. Parasitism levels from egg mass collections will give us an idea of the WBC population reduction contributed by Trichogramma.

Project Timetable

March, 2106: Meet with collaborating farmers to explain details of the study and explore a process for identifying potential release fields later in the season.

July, 2016: Visit farms to identify release fields and set up pheromone traps. Check traps weekly. Start wasp releases.

August – mid-September 2016: Continue wasp releases. Scout for egg masses in sweet corn. Evaluate WBC damage in field corn and dry beans.

October 2016: Analyze data, summarize results and meet with collaborating growers to discuss. Look for opportunities to present results at grower meetings.

November-December, 2015: Prepare report and write newsletter articles. Prepare presentations for grower meetings.

Outreach Plan

I will write newsletter articles about the results of this project for publication in regional vegetable and field crops Extension program newsletters as well as newsletters of organic farming organizations such as NOFA-NY. If results are positive, there may be an opportunity to discuss the project at an annual dry bean field meeting organized by a Cornell Cooperative Extension colleague. Positive results will also be blogged and tweeted through the NYS IPM Blog and Twitter feed. I will also look for opportunities to share the results with organic growers through presentations at organic farming meetings and conferences. The report for this project will be posted on the NYS IPM Program web site (http://www.nysipm.cornell.edu), briefly included in the NYS IPM annual report, in addition to submitting a final report to the SARE web site.