Research Shows Efficacy of Herculex I Trait Against Major Corn Pests

• Pioneer and universities conducted replicated trials to evaluate the performance of the Herculex¹ I Insect Protection trait against black cutworm, fall armyworm and corn borer.
• In small-plot barrier studies, the Herculex I trait offered very good protection from cutting by black cutworm. Control was equivalent to that of soil insecticides applied at planting.
• Under high black cutworm pressure, a low level of cutting (5-10%) still occurred in Herculex I hybrids. More research in field-sized plots with natural infestations of black cutworm is helping to further define the level of protection.
• Pioneer® brand hybrids with the Herculex I trait also provided excellent protection against fall armyworm and European and southwestern corn borer larval feeding.
• This Crop Insights will present university and Pioneer small-plot efficacy data for Herculex I technology against these major corn insect pests.

Herculex I insect protection is the first in a new generation of Bt traits for corn. This technology helps growers maximize their return on each acre by protecting corn plants against a broad spectrum of insects including corn borer, black cutworm, fall armyworm and western bean cutworm. Both Dow AgroSciences and Pioneer are aggressively pursuing additional regulatory approvals around the world.

Against corn borer and fall armyworm, efficacy of Pioneer hybrids with the Herculex I insect protection trait is rated as excellent. Protection against black cutworm and western bean cutworm is rated as very good. Western bean cutworm control is discussed in a separate Crop Insights article. (http://www.pioneer.com/usa/agronomy/insects/western_bean_cutworm.xml) To further document the performance of Pioneer hybrids with the Herculex I trait under various insect infestation levels, research trials were conducted in several major corn-producing states.

Small plot replicated trials were conducted by Pioneer Agronomy Sciences researchers from 2001 to 2003 at five locations: Mankato, MN; York, NE; Johnston, IA; Princeton, IL; and Windfall, IN. Treatments were replicated four times at each location in a completely random design. In all trials, a plot consisted of five corn plants bordered by a 14-gauge steel rectangular barrier 42 inches long by 12 inches wide by 9 inches deep. The metal barrier was inserted into the soil to a depth of approximately three inches. When corn plants reached the V1 to V2 stage of development, three third-instar black cutworm larvae per plant (15 per barrier) were placed inside the metal enclosures.

Corn plants wilting due to cutting by black cutworm.

At various days after infestation (DAI) with the black cutworm larvae, the number of plants cut at or below the soil surface was recorded. Dead-hearted plants were counted as cut plants. Results of these barrier trials are shown below.

Figure 1. Percent cut plants in Herculex I and base genetics
barrier trial plots for five locations in 2001. Pioneer Agronomy Sciences Research.

"Deadheart" symptoms due to black cutworm feeding in a conventional corn plant.

At the Mankato, MN location in 2001, 70 percent of the base genetic plants were cut while no Herculex I plants were cut. The Johnston, IA, Princeton, IL, and Tipton, IN locations also had no plants cut in the Herculex I plots 14 DAI, while the base genetics had 25%, 15% and 10% cut plants, respectively. Although the level of cut plants for the untreated check was relatively low in these locations compared to Mankato, the level was still well above what would be considered an economic threshold.

2002 plot results are shown by location below:

Figure 2. Percent plants cut by black cutworm for various treatments in barrier trials at Princeton, IL, 2002. Pioneer Agronomy Sciences Research.

Figure 3 Percent plants cut by black cutworm for various treatments in barrier trials at Windfall, IN, 2002. Pioneer Agronomy Sciences Research.

At the Princeton location, 45 percent of the plants were cut in the untreated check, and 40% in the YieldGard² plots (YieldGard does not claim black cutworm control), but only five percent of the plants were cut in the Herculex I plots. At the Windfall location, 25 percent of the plants were cut in the untreated check, with no cut plants in Herculex I plots. The Herculex I trait provided protection from black cutworm damage equivalent to planting-time granular insecticides at these two trial locations. At the three additional Agronomy Sciences locations in 2002, the percent cut plants in the untreated check plots was too low to make meaningful treatment comparisons.

In 2003 testing the insecticide seed treatments Poncho³ 250 and Poncho 1250 were also evaluated for control of black cutworm (Figure 4).

Barrier trials infested with 3rd or 4th instar BCW larvae at the rate of three larvae per plant at V2 stage of corn development.

Figure 4 Black cutworm efficacy, mean of five locations
(14 days after infestation), 2003. Agronomy Sciences Research.

When data across five locations were combined for analysis, Herculex I insect protected plants provided very good protection against cutting from black cutworm larvae. Protection was significantly better than Poncho 250 and YieldGard Corn Borer-protected plots.

Herculex I plots were also treated with Poncho 250 seed treatment to evaluate if the seed treatment would enhance the level of insect control compared to Herculex I plants alone. Plots treated with Herculex I + Poncho 250 had numerically lower percent plants cut compared to the Herculex I only plots, but the differences were not statistically significant. This is similar to results from previous testing in that the addition of a seed treatment to Herculex I-treated plots did not significantly decrease the level of cutting by black cutworm larvae compared to Herculex I plants without a seed treatment.

Two granular soil insecticides were also evaluated in this trial. Plots treated with Force⁴ 3G or Lorsban¹ 15G soil insecticides at planting had a level of cutting by black cutworms that was not significantly different from Herculex I-treated plots. Similarly, Poncho 1250-treated plots had levels of cutting that were not significantly different compared to Herculex I-treated plots.

When data were combined across locations for analysis, Poncho 250-treated plots had a level of cutting that was not significantly different from the untreated check, but was significantly higher than the percent of cut plants compared to Herculex I, soil insecticides and Poncho 1250.

Conventional corn plant cut by black cutworm larva.

University researchers also evaluated Herculex I insect protection for efficacy against black cutworm in 2001 and 2002. Trials were conducted at Purdue U., U. of Illinois, U. of Missouri, U. of Kentucky, and Iowa State U. Data from these trials were averaged across locations and years and are presented in Figure 5. The means in this figure represent a combined 10 environments (location-years), for a total of 40 replications of data. All are artificially infested barrier trials.

Figure 5. Percent cut plants in Herculex I and base genetics barrier trial plots for ten university locations, 2001-2002.

Percent cutting across these 40 reps of university data is significantly reduced in Herculex I plots compared to the untreated check plots. Overall, the Herculex I trait showed a significant reduction in percent cut plants in all barrier trial studies. Based on these results, Pioneer hybrids with the Herculex I trait are rated a 7 on the Pioneer 1-9 scale for black cutworm efficacy. However, these studies predict that under high black cutworm pressure, a low level of cutting may still occur. Pioneer will continue to collect data from larger field-sized plots under natural black cutworm infestations to further characterize the level of protection of Herculex I hybrids against black cutworm.

Fall armyworm feeding damage to conventional corn plant.

Herculex I technology is rated as excellent for control of feeding by fall armyworm larvae. To help verify this rating, University researchers at Auburn U., U. of Georgia, and North Carolina State U. conducted fall armyworm efficacy trials in 2001. In these trials, plots were planted late to encourage natural infestation by fall armyworm, but plots were also manually infested with fall armyworm egg masses. Plots were evaluated at 7 and 14 days after manual infestation. Percent of whorls infested by fall armyworm was recorded for Herculex I and base genetics plots (Figure 6).

Figure 6. Percent of whorls infested with fall armyworm in plots of Herculex I hybrids compared to base genetics at two university locations, 2001. Data recorded 7 and 14 days after manual infestation with fall armyworm egg masses.

Fall armyworm larva feeding on leaf of conventional corn.

In addition, plots were evaluated on a 0-9 scale for leaf feeding damage 7 and 14 days after manual infestation at two of the locations (Figure 7).

*Davis Rating scale: 0 = no damage, 9 = whorl & furl leaves almost totally destroyed.

Figure 7. Fall armyworm leaf damage ratings in plots of Herculex I hybrids compared to base genetics at two university locations, 2001. Data recorded 7 and 14 days after manual infestation with fall armyworm egg masses.

As the graph above demonstrates, Herculex I hybrids offered excellent protection from fall armyworm feeding. Based on these and other field studies, Herculex I hybrids have been assigned a rating of 8 on the Pioneer 1-9 scale.

Both Pioneer and university data have consistently demonstrated that Herculex I technology provides excellent protection from tunneling by European corn borer and southwestern corn borer (Figures 8 and 9). Herculex I hybrids have been assigned a rating of 9 on the Pioneer 1-9 scale for both European corn borer and southwestern corn borer efficacy.

Figure 8. Stalk tunneling from European corn borer in Herculex I plots compared to untreated base genetics. 7 locations, 2001. Pioneer Agronomy Sciences Research.

Figure 9. Stalk tunneling from southwestern corn borer in Herculex I plots compared to untreated base genetics plots from three university locations, 2001.

The relationship between number of cavities and percent yield advantage of Pioneer brand hybrids with Herculex I insect protection compared to genetically similar hybrids without Herculex I is depicted in Figure 10. These data indicate that over 49 locations from 2001-2003, Pioneer hybrids with Herculex I insect protection gave an average grain yield advantage of approximately 7 percent for every corn borer cavity per stalk.

Figure 10. Relationship between number of ECB stalk cavities and grain yield advantage of Pioneer hybrids with the HXI trait compared to genetically similar hybrids without the HX I trait, 2001-2003 (49 environments).