Implementing a Biointensive Strategy for Caterpillar Control in Sweet Corn

Implementing a Biointensive Strategy for Caterpillar Control in Sweet Corn

Summary

A bio-intensive strategy for the control of caterpillar pests of sweet corn is being implemented in commercial fields on eight farms. Each farm is testing the strategy in multiple plantings, using direct silk applications of Bacillus thuringiensis and corn oil to control corn earworm and foliar applications of Bt for European corn borer. Significantly improved control was achieved in all plantings in 2000, averaging 83% ears with no caterpillar damage to the tips in the oil treatments compared to 59% without oil. The results were significant again in 2001: 82% of the oiled ears had undamaged tips, compared to 62% in the non-oil treated ones. Oil reduced both numbers and size of caterpillars. Experiments to determine optimal timing of oil for best ear quality showed ear length remains unaffected by oil, but silks from the top 10 kernels develop late and tip fill is reduced when oil is applied early in ear development. Analysis to determine the oil application time for the best caterpillar control with the least amount of undeveloped (“cone”) tip is still in progress.

Objectives/Performance Targets

The objectives of this project are to evaluate the efficacy and cost of this integrated bio-intensive strategy on eight cooperating farms throughout New England, to conduct a qualitative assessment of the impact of using the caterpillar control strategy on production and marketing of sweet corn and other crops on the same cooperating farms, and to develop a better understanding of how direct silk applications of oil influence the developing ear kernels and larval mortality, in order to determine the optimal timing of oil treatments for highest ear quality.

Accomplishments/Milestones

We have completed the field research for all of the experiments in our three objectives. We will be conducting one more season of research on some experiments that we started this year. Other than those three experiments (see appendix) we are in the process of analyzing the data.

This year we saw the commercial production and marketing of the Zea-later oil application device. It is being manufactured by Conlet Plastics in Ct, and exclusively distributed by Johnny’s Selected Seeds in Maine. This year, the first in commercial production, all 50 of the first batch of Zea-laters produced were sold.

Impacts and Contributions/Outcomes

Objective 1: This was the second year of this experiment. On each of eight farms three blocks of corn were planted. The first plots were planted between May 22 and May 30, the second between June 4 and June 12, and the third between June 17 and June 25. Each block was at least 8 rows wide by 200′ long, and using a split block design, contained oil and no-oil sections. The growers treated the top ear of every corn plant in the oiled block with a mixture of Bt and corn oil (.5ml oil; .5 lb per acre Dipel DF Bt). To achieve better control of the European corn borer than last year, a foliar spray of Bt was applied to the whole block of corn on each farm in each planting, covering the oil as well as the no-oil sections. At harvest, 100 ears each from the control and oil-treated sections of each block were scored for number, size and type of caterpillars, as well as damage to the tip, side, and husk.

A pooled analysis of all of the blocks on all of the farms shows a statistically significant increase in the percentage of corn without tip damage, from 62% to 82% in the untreated verses the treated (oiled) samples. The range in improvement in the amount of tip damage on each farm varied from 7% to 43%, with the highest levels of improvement generally occurring on farms with the greatest pest pressure. While last year significant differences in the amount of side damage were found in many blocks, this year (2001) only two blocks showed a measurable difference. We attribute this to the more uniform application of the Bt foliar sprays between the farms. This year 5 of the plantings did not produce a crop, and one of the farms dropped out of the project.

Objective 2: Our qualitative assessment of the impacts of using this system on farms is on track: we have conducted pre- and post-season interviews, and will be following up with final interviews this winter. From the information gathered to date, we know that the attrition of one of the farms from the project is due to the high costs of land rental and fertilizer, with low revenue anticipated in the wholesale market, and is not directly related to the pest control issue. A detailed write-up will be provided in our final SARE report later this year.

Objective 3: Experiment 1: A key question is how the application of either the oil or Bt applied directly into the husk affects the growth and development of the ear. Ears and silk growth were measured over a 12-day period (after 50% of plants showed silk), with the treatments applied on the third day of silk growth. The oil/Bt treatment did not affect the growth of the ear as measured by ear length, circumference or rate of growth; however, the development of approximately the last ten kernels at the tip was stopped. At the time of oil application the silks that are connected to these tip kernels are still within the husk and receive a significant amount of oil as the oil moves down the silk channel. The oil seems to cause cone tip—undeveloped kernels—by interfering with pollination of the silks.

Experiment 2: Conducted in 2000 and 2001. To determine what day to apply corn oil to achieve the best corn earworm control, we applied the oil/Bt mixture to corn ears every day from day 3 through 11 after 50% of the field had silk emergence. No other insect controls were applied. The experiment was conducted twice, with two staggered plantings for evaluation under different pest pressures. The corn was harvested at maturity and evaluated for length of ear, length of cone tip, number, type and size of caterpillars, and the amount and location of damage. Results suggest that application of oil prior to the 4th or 5th day results in cone tip. The later the treatment was applied to the silk channel, the more likely the opportunity for full pollination and tip development; however, this has to be weighed against the time of caterpillar pressure. Analysis of effects of timing on pest damage is in progress.

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