Integrating Microbial Insecticides and Oils into Sweet Corn IPM in Massachusetts

Integrating Microbial Insecticides and Oils into Sweet Corn IPM in Massachusetts

Summary

Summary
Fresh market sweet corn is a major vegetable crop in the Northeast. Caterpillar pests of corn, which feed directly on sweet corn ears inside the husk, cause from 10 to 100 percent unmarketable ears if left uncontrolled. Currently, farmers have few alternatives to restricted-use, broad-spectrum insecticides that deplete beneficial insects and have high mammalian toxicity. This project evaluated foliar and direct silk applications of microbial insecticides and vegetable oils as alternative methods which pose less risk to applicators and the environment and which conserve natural enemies.

Key Findings
Bacillus thuringiensis (Bt) products can be integrated into a standard IPM system for European corn borer (ECB) control as a direct replacement for conventional insecticides with no extra cost to growers and with positive benefits to the agro-ecosystem.

In late-season corn, commercially acceptable levels of control (90-100 percent undamaged ears) were achieved in experiments where foliar applications of Bt were used in combination with a direct-silk oil treatment.

Use of biointensive methods in corn will result in higher populations of beneficial insects in corn and other crops on diversified vegetable farms with increased suppression of other insect pests such as aphids.
Fourteen of the 17 participating growers were satisfied with the control they achieved with Bt and plan to use it in the future. Reasons for choosing Bt over conventional products were applicator safety, easier relations with neighbors, shorter re-entry and preharvest intervals, and conservation of their beneficial insects.

Objectives
1.Evaluate the effectiveness of commercial Bt products against European corn borer and fall armyworm in fresh market sweet corn in Massachusetts.
2.Develop an alternative control for corn earworm using an oil and Bt barrier applied directly to the silk.
3.Integrate alternative insect controls into current Integrated Pest Management (IPM) systems used by sweet corn growers in the Northeast.

Method and Findings
In early season corn, ECB is the primary insect pest. Commercial Bt products were tested in 1994-1996, in 34 trials conducted on 17 farms in Massachusetts. Standard sweet corn IPM scouting methods, thresholds and spray intervals (5-7 days) were used. Bt products gave equal control of ECB compared to conventional materials. Higher numbers of beneficial insects were present in Bt-treated plots than conventional plots following insecticide applications. Eighty-two percent of participants were satisfied with the control they achieved and plan to use Bt in their early corn in the future.

Replicated experiments showed that weekly applications of Bt products were as effective as twice-weekly applications in controlling ECB. The cost per acre of using Bt products is equal to conventional products. The environmental impact as measured by the environmental Impact Quotient (EIQ) is 6.99 for Bt vs. 21.64 for conventional insecticides. An average of 1.0 pt AI/acre of restricted pesticide would be eliminated by adoption of Bt products for early-season ECB control. These results show that Bt products can be integrated into a standard IPM system for ECB control as a direct replacement for conventional insecticides with no extra cost to growers and with positive benefits to the agro-ecosystem.

In late-season corn (harvested in August and September), second-generation European corn borer (ECB) and corn earworm (CEW) cause up to 100 percent damaged ears. Application of an oil/Bt barrier to the silk at the tip of the ear causes mortality to any caterpillars that enter through the silk channel. Oil barrier treatments consistently yielded 2-3 times more marketable ears than untreated controls, with results ranging from 65 percent to 100 percent undamaged ears compared to 18 percent to 87.5 percent clean in controls.
Commercially acceptable levels of control were achieved in experiments where foliar applications of Bt were used in combination with a direct-silk oil treatment. A hand-held oil applicator was designed and built which reduces the labor required for direct treatment of silks. Growers who tested the oil applicator reported positively on its efficiency. The cost for this late-season biointensive system is $107 to $137 per acre compared to $108 for standard IPM and $172/acre for conventional, non-IPM management.

This strategy is of greatest interest to organic growers who currently have no method of control for corn earworm and face significant losses due to corn earworm damage. If it proves to be reliable and cost-effective, it will also be of interest to IPM sweet corn growers with 10-15 acres who are seeking alternative methods.

Conclusion
The results of this project are applicable throughout northeastern and central North America, where fresh market sweet corn has a similar pest complex. For growers currently using registered broad-spectrum insecticides, Bt foliar sprays provide an alternative that is no more costly and can be readily integrated into current practice.

For organic sweet corn growers who currently see retail sales decline and are prohibited from wholesale markets, a viable organic method will expand sales, production and profitability.
Reported December 1997.

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