Corn Earworm IPM Educational Program in Utah

Sweet corn is grown on approximately 1,500 acres in Utah and marketed via roadside stands and local grocery stores. The corn earworm, Helicoverpa zea, is a major insect pest that feeds on the corn ear and allows entry of secondary insects and rot-inducing molds. Heavily damaged ears cannot be marketed. Growers can control corn earworms (CEW) by applying insecticides several times while the ear is maturing.

In many cases, the insecticide applications have been based on when the neighbor sprayed or on a set calendar schedule. In 1994, an integrated pest management (IPM) educational program on corn earworm control was implemented due to grower interest in improved pest control strategies. The program was funded by U.S. Department of Agriculture Cooperative Science, Education and Extension Service Smith-Lever 3D funds via a competitive Utah IPM mini-grant program.

Lewis (1982, p. 2) indicates that the adoption of a new farming technique is no trivial matter: "Even the strongest arguments for a change in a production system can easily be ignored, because in any change the risk of lost income, lost credit, lost production is just too great. The Land Grant concept provides for a system of interpreting, demonstrating, and implementing agricultural knowledge, through Extension." Barao (1992) points out that "Instruction and demonstration of new technology within the controlled setting of a university research farm may not encourage farmers to adopt the technology for their farm, which have distinct and different resources." Our goal in this program was to demonstrate IPM practices in on-farm plots and to teach growers how to implement the practices on their own farm.

An IPM demonstration project was conducted to determine if insecticide applications to sweet corn could be reduced. Corn earworm moths were monitored using Hartstack-style net traps with Scentry and Hercon pheromone lures. Traps were placed in commercial sweet corn fields in several locations across Utah from 1994 to 1997. Traps were monitored by Extension agents or summer interns. Many plots contained a no-spray control that was harvested to monitor trap effectiveness.

With Extension doing the initial monitoring, it was demonstrated that the traps were providing good information as to whether an insect control spray was needed or not. In later years, growers were encouraged to do the monitoring. In addition, daily temperature data were collected to verify a degree day model that predicted timing of moth population levels (Scott, Baird, and Homan, 1984).

Trapping identified the appropriate dates to begin spraying in the spring and when sprays could be eliminated during the season. Growers who followed IPM guidelines based on trapping data could successfully eliminate up to three insecticide applications that would have normally been applied. Comparison of trapping data from different counties showed that earworm moths emerged at approximately the same time in southern and northern areas of the state. The degree day model proved to be effective in predicting the low earworm moth population between generations.

Once reliable information had been obtained, a series of state-wide vegetable grower meetings were held in 1995, 1996, and 1998 to explain IPM moth monitoring techniques and suggested spray programs. A total of 93 growers attended. The meetings opened the door to other cooperative projects with growers such as development of a sweet corn enterprise budget and discussion of value-added marketing. Growers were trained to monitor CEW on their own fields by Extension staff making farm visits and providing reference materials such as color pictures of moths, mounted samples of actual moths, data recording forms, and IPM guidelines for insecticide applications. Extension provided traps and lures to growers who were willing to monitor their fields and record moth counts and insecticide application dates.

A five-page fact sheet on the biology and control of the corn earworm was prepared. The publication included color pictures of the corn earworm moth, pupa, and larva and graphics illustrating a typical moth flight pattern for Utah. Detailed instructions are given on how to monitor moths using pheromone net traps and degree days. IPM guidelines were included to interpret monitoring data, adjust insecticide applications, and explain organic, cultural, and biological control options for CEW. A list of currently registered chemical insecticides was included in the bulletin. The bulletin was introduced at the state vegetable growers meeting and was made available at all county Extension offices. [Available from Utah State University Bulletin Room, Logan Utah, 84322-8960.]

One of the most critical questions to come out of the on-farm demonstrations was the interval between pesticide applications based on moth levels. While not able to answer this question from on-farm trials, the use of a more controlled setting on a university research farm was used to determine the proper spray threshold. Growers were invited to a field day at the farm in 1996 to see the plots and obtain results. The general guidelines that evolved were:

Spray every 5 days when moth catch is High (more than 1 moth/night average)

Spray every 7 days when moth catch is Low (0.2-1.0 moths/night average )

No spray is necessary if below 0.2 moths per night average

Major findings from IPM plots with growers were:

1. Moth monitoring was effective in timing insecticide sprays when done with an effective lure, proper pest identification, and appropriate moth threshold levels.
2. Insecticide use could be reduced by following IPM guidelines. If we assume a $20 per acre spray cost and 3 sprays saved per season on 1500 acres of corn grown, this would be a savings of $90,000 per season when fully adopted. There would also be a substantial reduction in pesticide introduction into the environment.
3. Moth spray thresholds from other states (Dill and Handley, 1996; Ferro and Weber, 1988) were validated that showed that if less than 0.2 moths were caught per night then no sprays were necessary.
4. Moth levels varied by geographic location. Traps less than 1 mile apart were less variable than those more than 10 miles apart.
5. A degree day (DD) model with lower and upper thresholds of 55 F and 95 F could be used to predict an interval between CEW generations. This interval of little or no moth activity occurred between 1100 and 1300 DD. The average time of the interval was an 8-10 day period from the end of July through the first part of August.
6. That CEW pupae do not overwinter in northern Utah but may overwinter in southern Utah.
7. That growers need to monitor their fields for the best information and not rely on county-wide surveys.

Bohlen (1955) indicates that the adoption of a new idea generally follows a sequence from the time an idea is formed until it becomes generally accepted. In this diffusion process people may be classified into types based upon the sequence in which they adopt new ideas as follows: innovators, community adoption leaders, local adoption leader, and later adopters. The authors received in-service training several different times on the adoption process and how Extension program participants use what they learn (Bennett, 1975; Boone, 1985), but the CEW project was a very visible example of the process in action.

In a survey of 23 sweet corn growers in the state, Drost, Long & Hales (1998) found that research and Extension efforts on IPM with corn earworm appeared to be paying dividends. Growers with positive feelings about sustainable agricultural practices tend to be more receptive to and practice more IPM techniques. In addition, if farmers employ IPM practices, they are also more aware of issues related to nutrient management (r=0.55; P0.01). Drost et al. (1998) also found that sweet corn land owners were more likely to practice IPM on their farms than growers who rented land.

With respect to using IPM practices for CEW control in Utah, the innovators and some community adoption leaders are following recommended practices. To date, approximately 25 growers out of 174 total growers statewide are using some form of IPM. Those growers using IPM manage about 400 acres of sweet corn. Complete adoption is still a few years down the road. The most gratifying part of this project was seeing the enthusiasm and dedication of the innovators as they worked with Extension agents and specialists and neighboring farmers to implement IPM practices.

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Boone, E.J. (1985). Developing programs in adult education. Englewood Cliffs, NJ: Prentice-Hall.

Dill, J.F., & Handley, D.T. (1996). Managing insect pests of sweet corn. University of Maine Cooperative Extension, Bull. No. 5101.

Drost, D., Long, G., & Hales, K. (1998). Targeting Extension efforts for the adoption of sustainable farming practices. Journal of Extension [on line serial], 36(5). Available at http://www.joe.org joe October 1998 research 1.

Ferro, D.N., & Weber, D.C. (1988). Managing sweet corn pests in Massachusetts. Amherst: University of Massachusetts Cooperative Extension, AG-335:8.

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Scott, D.R., Baird, C.R., & Homan, H.W. (1984). Timing corn earworm control. Moscow: University of Idaho Cooperative Extension, Current Information Series No. 366.