No. 24/November 7, 1997
Efficacy of Bt-Corn in Illinois in 1997
A lot of people have been calling to ask if we have completed our evaluation of the Bt-corn efficacy trial we established in Urbana this year. John Shaw and Jimmy Finger, entomologists with the Illinois Natural History Survey and the leaders of this effort, coordinated the evaluation of the trial on October 7, 8, and 10; and they recently completed their analyses. As you read this article, they are double-checking the data and preparing the information for a report. Consequently, the data presented with this article still are somewhat preliminary. The carefully scrutinized results of all insect-control evaluation trials in 1997 will appear in the final report under John Shaw's supervision.
First, we'll offer an overview of our 1997 Bt-corn trial. Eight companies provided us with Bt-corn hybrids, and five of the companies provided us with non-Bt-corn hybrids. Although some of the Bt-corn hybrids in our trials were commercially available in 1997, others were "experimental" and were not sold in 1997. The following companies gave us hybrids for evaluation: AgrEvo, Cargill, DeKalb, Garst, Mycogen, Northrup King, Novartis, and Pioneer. Twenty-two hybrids were planted in the trial.
The trial was planted on May 22, 1997. Each hybrid was planted in a plot that was 4 rows (30-inch spacing) wide by 30 feet long. All plots were thinned to 35 plants per row. The experimental design was a randomized complete block with six replications. All plots were manually infested (15 plants in each of the center two rows of each plot) with egg masses to simulate infestations by both first-generation (egg masses applied on July 11) and second-generation (egg masses applied on August 14) European corn borers. In addition, just like all growers' fields in the area, our trial was exposed to a rather significant natural infestation of borers.
To simulate conventional control of corn borers, one plot of non-Bt-corn was treated with Pounce 5 to 6 days after each manual infestation was completed. Pounce 1.5G was applied in a band over the rows to control first-generation corn borers, and Pounce 3.2EC was broadcast over the rows to control second-generation corn borers.
Although a large number of evaluations were conducted in the plots, only percentages of plants with cavities, mean cavity lengths, and yields are reported with this article (Table 1). Other evaluations and measurements conducted were stand counts; ratings of aphid infestations; numbers of cavities per plant; numbers of larvae per plant, shank, and ear; ratings of ear damage; percentages of stalks broken above and below the ear; percentages of ears on the ground; percentages of plants with stalk rot; and percentages of ears that were poorly developed. John Shaw and Jimmy Finger deserve a great deal of credit for such a thorough experimental effort.
Table 1. Results of the 1997 University of Illinois and Illinois Natural History Survey Bt-corn efficacy trial, Urbana.
|Hybrid||Mean % plants with cavities1,2||Mean cavity length (cm)1,2||Mean yield (bu per A)2,3 |
|Pioneer 34R06 (Bt)||0.0 a||0.00 a||200.8 a|
|Pioneer 33A14 (Bt)||13.0 a||0.57 a||194.9 ab|
|Pioneer 3489 (non-Bt) + Pounce4||28.0 bc||1.13 a||183.2 abc|
|DeKalb DK 580 (Bt)||38.0 c||2.02 a||174.9 a-d|
|Northrup King NK 7070 (Bt)||3.3 a||0.08 a||172.4 a-d|
|Cargill 7821 (Bt)||1.7 a||0.02 a||172.2 a-d|
|Pioneer 3489 (non-Bt)||97.0 e||9.93 b||171.9 a-d|
|Mycogen 2787 (Bt)||53.0 d||3.32 a||166.5 bcd|
|Cargill 7770 (non-Bt)||97.0 e||13.50 c||164.2 cd|
|DeKalb DK 566 (Bt)||15.0 ab||0.33 a||163.2 cd|
|DeKalb DK EXP 152 (Bt)||0.0 a||0.00 a||156.2 cd|
|Novartis Maximizer 454 (Bt)||53.0 d||3.20 a||154.5 cd|
|Northrup King NK 7070 (non-Bt)||100.0 e||16.35 d||152.5 d|
|DeKalb DK EXP 255 (Bt)||0.0 a||0.00 a||149.7 d|
|DeKalb DK EXP 057 (Bt)||0.0 a||0.00 a||148.6 d|
|DeKalb DK 493 (Bt)||65.0 d||2.70 a||146.9 d|
|Garst EXP 83 (Bt)||1.7 a||0.13 a||--5|
|AgrEvo 97VCE (Bt)||1.7 a||0.03 a||--|
|Garst EXP 85 (Bt)||3.3 a||0.03 a||--|
|AgrEvo 97VCB (Bt)||3.3 a||0.10 a||--|
|Garst EXP 83 (non-Bt)||90.0 e||11.70 bc||--|
|AgrEvo 97VCE (non-Bt)||90.0 e||10.33 b||--|
|AgrEvo 97VCB (non-Bt)||98.0 e||12.18 bc||--|
1A total of 60 plants were evaluated (5 plants in each of two plot rows X 6 replications).
2Means in the same column followed by the same letter are not significantly different (P = 0.05; Duncan's New MRT).
3Yields were determined from 180 plants per "treatment" (30 plants per plot X 6 replications).
4Pounce 1.5G was banded over the row at 10 lb of product per acre on July 17 to control first-generation corn borers. Pounce 3.2EC was broadcast over the plots at 0.15 lb a.i. per acre on August 19 to control second-generation corn borers.
5Evaluation of yield was not conducted.
Because so many folks focus on corn yields, the data in Table 1 are arranged in order of decreasing yields (right-hand column). However, yields of some hybrids were not evaluated. Questions to ask when you examine the table are these: Did Bt-corn prevent infestation by European corn borers? If a Bt-corn hybrid prevented the establishment of corn borer larvae, did it yield well? If a Bt-corn hybrid did not prevent establishment of corn borer larvae, did it yield well? Did any non-Bt-corn hybrids yield well despite the infestation? The data in Table 1 provide some interesting answers to these questions.
Corn borer control. Six of the hybrids we evaluated were non-Bt-corn hybrids; and, if Pounce was not applied, the percentage of non-Bt-corn plants infested with corn borers was very high (90% or more for all six hybrids). These percentages of infestation among the non-Bt-corn hybrids all were significantly greater than the percentages of all Bt-corn hybrids. Not surprisingly, because the concentration of the Bt toxin declines in Novartis's and Mycogen's Bt-corn hybrids after pollination, Mycogen 2787 and Maximizer 454 had significant infestations of corn borers (53% of the plants with cavities). Two of DeKalb's Bt-corn hybrids also had significant infestations of corn borers [38% and 65% of the plants with cavities for DK 580 (Bt) and DK 493 (Bt), respectively]. Pioneer 3489 treated with Pounce for control of both first- and second-generation corn borers also had a significant infestation (28% of the plants with cavities). With the exceptions noted, all other Btcorn hybrids kept infestations of corn borers at or below 15%; ten of the Btcorn hybrids kept infestations of corn borers at or below 3.3%. The data regarding mean cavity length per plant reflect the same trends.
Yield. This is the tale of the tape, so to speak. None of the yields were poor, and some of the yields were outstanding. With two of their Bt-corn hybrids, Pioneer captured top honors in the yield column. Also, Pioneer 3489 treated with Pounce yielded near the top. In fact, Pioneer 3489, although heavily infested with corn borers (97% of the plants with cavities, an average of 9.93 inches of tunneling), yielded quite well. This hybrid obviously demonstrates tolerance to infestation by corn borers. This and other tolerant hybrids would be outstanding choices for use in refuges in a resistant-management scheme. Other high-yielders (with an 'a' in the column indicating yields were not significantly different from the yields of the hybrids previously mentioned) were DK 580, NK 7070, and Cargill 7821, all Bt-corn hybrids. Despite a significant infestation of corn borers (53% of the plants with cavities), Mycogen's 2787 Bt-corn hybrid yielded well, not significantly different from the yield of Pioneer 33A14.
The most important messages our results provide are these:
- In general, most Bt-corn hybrids provide excellent control of European corn borer larvae.
- Bt-corn hybrids yield well if the gene for expression of the Bt toxin has been placed in a hybrid with good-yielding attributes.
- Even if a Bt-corn hybrid is infested with corn borers, yield may be acceptable.
- Some non-Bt-corn hybrids tolerate infestations of corn borers and produce acceptable yields.
- A conventional insecticide treatment for corn borers can produce good results, both in control and in yield.
As we attend meetings of university and seed company representatives throughout the next few months and learn about results from other states, we'll share them with you.
Kevin Steffey and Mike Gray, Extension Entomology, (217)333-6652