European Corn Borer Management with Herculex® I Insect Protection

• Pioneer brand hybrids with Herculex® I insect protection and Pioneer hybrids with the YieldGard® Corn Borer (YGCB) gene were tested against base genetic hybrids at locations with low, medium and high corn borer infestation levels.
  
• Hybrids with the Herculex I or YGCB gene statistically outperformed the base genetic hybrids for all measured traits at both low and high corn borer infestations, and at all locations combined.
  
• Pioneer hybrids with Herculex I insect protection and Pioneer hybrids with the YGCB gene performed nearly identically for ECB control at low, medium and high corn borer infestations, and at all locations combined.
  
• Data from 2001-2002 indicate Pioneer hybrids with Herculex I insect protection gave an average grain yield advantage of approximately 6 percent for every corn borer cavity per stalk, compared to base genetics hybrids.

Herculex I insect protection is the first in a new generation of Bt traits that provide additional pest management options and increased value to corn growers. The Herculex I gene protects corn plants against a broad spectrum of insects, including European corn borer (ECB), southwestern corn borer, black cutworm, and fall armyworm. In addition, these hybrids contain the LibertyLink³ gene, allowing application of Liberty³ herbicide for post-emergence grass and broadleaf weed control. Both Dow AgroSciences and Pioneer are aggressively moving ahead with regulatory approvals around the world.

Corn borer pressure varies widely due to geography and weather (Figure 1). Because of this variation, Pioneer has conducted studies to evaluate its hybrids under low, medium and high corn borer infestations. This Crop Insights reports on the results of these studies.

Figure 1. Percent of corn borer-infested plants at harvest.
Pioneer on-farm strip trials, 2002.

The primary objective of Pioneer research studies conducted throughout the Corn Belt was to determine the effectiveness of Pioneer corn hybrids containing the Herculex I trait in controlling damage from European corn borer and southwestern corn borer. The studies were designed to quantify the yield advantage of Pioneer corn hybrids containing the Herculex I trait over base genetic hybrids under various levels of corn borer infestation. In addition, researchers focused on comparing the performance of Pioneer hybrids with the Herculex I gene to that of Pioneer hybrids with the YieldGard Corn Borer (YGCB) gene.

Pioneer hybrids with Herculex I insect protection, Pioneer hybrids containing the YGCB gene, and genetically similar Pioneer hybrids not containing insect protection traits (base genetics) were planted in plots 17.5 feet long by 4 rows wide at 19 locations across the Corn Belt. Hybrids were nested within each trait segment, with four hybrids per trait segment at each location. Treatments were replicated four times per location.

Plots were evaluated for corn borer damage in late September to early October by examining 10 consecutive plants in each plot. Ears from these plants were examined for feeding damage from European corn borer or corn earworm, and presence of mold and ear shank tunneling. In addition, corn stalks were split lengthwise and the number of corn borer cavities and the total length of cavities were recorded. No distinction was made as to which insect species fed on the ear or which type of mold was present. Plots were harvested for grain yield, moisture and test weight.

Following stalk dissections, the 19 locations were grouped by infestation level for data analysis. Assignment of infestation level was based on the average corn borer tunneling per location as follows:

• Low: Less than 1 inch per stalk
• Medium: 1-2 inches per stalk
• High: Greater than 2 inches per stalk

Linear regression analysis was also performed to define the relationship between European corn borer infestation and yield response. Data from 2002 and 2001 studies were combined for this regression analysis.

Infestation levels of European corn borers were generally low at the testing locations in 2002, with 11 of 19 locations having low levels. Only two locations had high infestation levels at testing sites in 2002.

When data from all 19 locations were combined for analysis, Pioneer hybrids with the Herculex I gene and Pioneer hybrids with the YGCB gene statistically outperformed base genetic hybrids for all reported traits (Table 1). There were no statistically significant differences between Pioneer hybrids with the Herculex I and the YGCB gene for ECB control when data from all 19 locations were combined.

Table 1. Performance of insect-protected hybrids vs. base genetics averaged across 19 locations, 2002.

When data were grouped by infestation level for analysis, results were similar. Across 11 locations with low infestation levels, Pioneer hybrids with either the Herculex 1 or YGCB genes statistically outperformed base genetic hybrids for all traits (Table 2).

Table 2. Performance of insect-protected hybrids vs. base genetics averaged across 11 locations with low corn borer infestation levels, 2002.

Across 6 locations with medium infestation levels, Pioneer hybrids with either the Herculex I or YGCB gene statistically outperformed base genetic hybrids for all traits. There were no significant differences for any of these traits between hybrids with the Herculex I and the YGCB genes.

Corn borer cavity and resulting stalk rot in non-insect
protected hybrid.

Table 3. Performance of insect-protected hybrids vs. base genetics averaged across 6 locations with medium corn borer infestation levels, 2002.

Across 2 locations with high infestation levels, Pioneer hybrids with Herculex I insect protection and Pioneer hybrids with the YGCB gene statistically outperformed base genetic hybrids for all measured traits (Table 4). There were no statistical differences between the two types of insect-protected hybrids for ECB control.

Table 4. Performance of insect-protected hybrids vs. base genetics averaged across 2 locations with high corn borer infestation levels, 2002.

The relationship between number of cavities and percent yield advantage of Pioneer hybrids with the Herculex I trait over genetically similar hybrids without this trait is depicted in Figure 2. These data indicate that Pioneer hybrids with Herculex I insect protection gave an average grain yield advantage of approximately 6 percent for every corn borer cavity. This is approximately the same as the commonly used economic threshold formulas for insecticide treatment (generally, from 5 to 6 percent.)

Figure 2. Relationship of cavities per stalk to grain yield advantage of Pioneer hybrids with the Herculex I gene over genetically similar base genetic hybrids without the gene, 31 environments, 2001-2002.

Expected benefit in dollars per acre for using Pioneer hybrids with Herculex I insect protection at various European corn borer infestation levels is depicted in Figure 3.

Figure 3. Expected economic benefit from planting Pioneer hybrids with Herculex I insect protection at various levels of European corn borer infestation. Projections are based on a planting rate of 32,000k per acre, corn price of $2.50/bu, and yield level of 150 bu/acre.

Most damage at testing locations in 2001-2002 was from second-generation corn borers, which result in a lower yield loss than first generation damage. In a year with high levels of first generation damage, this relationship would be expected to show a greater return than is currently presented.

Union City, TN was the only testing location in 2002 where significant infestations of southwestern corn borer occurred. Pioneer hybrids with Herculex I insect protection and Pioneer hybrids with the YGCB gene statistically outperformed base genetic hybrids in southwestern corn borer protection. There was not a significant difference in protection from southwestern corn borer between hybrids containing Herculex I insect protection and hybrids containing the YGCB gene.

To protect the usefulness of Bt technology for as long as possible, the Environmental Protection Agency (EPA) has mandated that certain requirements be placed on its use. For corn growers, the primary requirement is establishing a non-Bt refuge to help deter development of resistance in corn borer populations. As a provider of Bt hybrids, Pioneer is committed to its mandated responsibilities to preserve this technology, including:

• conducting research on insect resistance management
  
• closely monitoring and reporting any development of resistant insect populations
  
• educating our sales force and customers in meeting the IRM requirements and assessing IRM compliance.

Complying with IRM requirements is critical to preserving the longevity and effectiveness of Bt corn technology, as well as a legal and stewardship obligation. To learn more about this important aspect of using insect-protected hybrids, refer to the Crop Insights entitled "Insect Resistance Management and Bt Corn."