John Van Duyn, North Carolina State University, Entomology Extension Specialist

European corn borer (ECB) , southern cornstalk borer (SCB) , and corn earworm (CEW) attack field corn stalks and ears and can cause serious corn yield losses of grain and silage. Losses may be manifested in smaller ears, lodging, fallen ears, and smaller plants.

Yieldgard ECB^® Bt corn was introduced in 1996, by Monsanto Company. Yieldgard ECB^® Bt corn contains the “Mon-810” gene (sold by many seed corn companies) or the “Bt-11” gene (sold by Syngenta Company). These genes, from the bacterium Bacillus thierengensis, have been engineered into the plant and allows corn plants to express CryIAb Bt toxin within most tissues. CryIAb toxin is very toxic to ECB (Photos 1 and 2) and SCB (Photos 3, 4, and 5). larvae that feed upon the plant. However, CryIAb is only moderately effective against CEW larvae feeding within the ears.

Prior to the advent of Yieldgard ECB^® Bt corn, and other Bt corn genotypes, growers generally suffered losses from these pests since control methods were difficult to use and economically problematic. These programs were based upon scouting, thresholds, and treating when & where needed. Aircraft were used to apply granular or spray insecticides Insecticides had to be applied with precise timing, and were moderately effective at best (aerially applied insecticide seldom killed more than 70% of ECB larvae on larger corn and few SCB and CEW were affected). Also, ECB and other caterpillar pests occurred in cycles, sometimes reaching pest level but usually staying below threshold levels designed for insecticide treatment. Therefore, technology that avoided having to manage a scouting and treat-as-needed program each season, and was also much more effective, was welcomed by corn farmers.

We began experimenting with Bt corn containing several different genes in the early 1990's and determined, at that time, that Yieldgard ECB^® genes were most effective under NC conditions. However, we did not understand the long-term benefit this technology may have under NC conditions, since it only provides an advantage when insects are above the economic injury level. In 1996, the Corn Growers Association of NC provided funding to study the benefit of Bt corn, and other biotech issues. The funding was continued for several years but ended in the early 2000's (as planned). However, we continued the research. Since 1996 we conducted trials each year, except one, that have compared near-isoline corn hybrids from many companies. A near-isoline comparison matches the Bt and non-Bt versions of the same hybrid and allows the researcher to measure the “Bt toxin effect” separate from the hybrid effect. Our goal has been to develop a long-term data base on Yieldgard ECB^® Bt corn performance over many years.

This web page presents results from those tests and reflects the possible value of Yieldgard ECB^® Bt corn to the corn farmer, at least in northeastern NC counties. The following figures presents yearly comparison data, long term summary of all yearly data, and contrasts of Yieldgard ECB^® versus Herculex^® Bt corn.

Since 1996, the corn grain yield in 49 out of 59 replicated comparisons (83%) favored the Bt version of the particular corn hybrid. Some years resulted in large yield differences, because pests were abundant, and small differences in low-pest seasons. In each year the average increase in yield would have paid for the approximate $7.00 / acre technology fee, although some specific hybrid comparisons were not profitable . Figures 9 shows the average income from each experiment and an overall long-term benefit of $24.91/ acre gross increase,calculated at $2.50/bushel, or approximately $17.91 profit per acre.

Dow Agrosciences Company and Pioneer Hybrid International Company recently introduced Herculex^® Bt corn. This raises the question of “how do the data presented, on Yieldgard ECB^®, relate to Herculex^®? Comparison tests conducted in 2003, showed that both Yieldgard^® ECB^® Bt corn and Herculex^® Bt corn were similarly effective against ECB (see Figures 10 and 11.) Other data not shown, indicates that Herculex^® is also active against SCB. Since ECB was the main yield reducing insect pests present in the Bt vs non-Bt near-isoline tests, we suggest that Herculex^® would provide similar benefit compared to Yieldgard ECB^®.

SHOULD THE CORN FARMER GROW YIELDGARD ECB^® OR HERCULEX^® Bt CORN HYBRIDS?

Yieldgard ECB^® corn performs well against ECB and SCB but only gives moderate control of CEW. Herculex^® Bt corn is effective against ECB and SCB but gives very little protection against CEW. However, stalk borers pose a more serious threat than the ear-feeding CEW. Yield differences (Bt Vs NBt) fluctuate with the intensity of ECB and SCB populations. Tests in the Tidewater area of NC have shown a benefit of $17.91 / acre / year, assuming $2.50 / bushel corn price and $7.00 / acre technology fee. Other advantages, not considered in this value, include a higher consistency of yield and some protection from rots, ear drop, and lodging. National averages of increased yield and profit are consistent to our local data. Other areas of NC may not show a similar benefit versus northeastern NC and some seasons will likely show little to no benefit. Growers should make their own choice based on historical ECB & SCB infestation and other experiences. If this information is not available, growers can plant side by side comparisons over several years (e.g. 3 to 4 seasons) and develop their own local data.

ACKNOWLEDGMENT

Corn Page

Other Resources

• North Carolina Agricultural Chemicals Manual
• North Carolina Cooperative Extension Service

This page (http://www.ces.ncsu.edu/plymouth/pubs/btcorn99.html) was created by John W. Van Duyn Ph D. Extension Entomologist and Wayne Modlin

Date Created 2/11/05.

Published by North Carolina Cooperative Extension Service

Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age, or disability. North Carolina State University at Raleigh, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.

CAUTION: The information and recommendations in these Notes were developed for North Carolina conditions and may not apply elsewhere.