Performance and Value of ECB-Resistant Hybrids

• Corn growers have more choices of Bt hybrids and maturities for 2001. Their decisions should be based on the value these hybrids provide to their operation.
• The value of resistant hybrids depends on the level of corn borer pressure. Because pressure varies, Pioneer conducted a 3-year study to evaluate its hybrids under different levels of corn borer infestation.
• Results from 70 locations showed that Pioneer hybrids with the YieldGard® gene:
  • had significantly less feeding damage and increased yield compared to non-resistant isolines under low, medium and high corn borer infestations.
  • provided a yield advantage of 8.7% over similar genetics without the YieldGard gene for every corn borer cavity present in the non-resistant hybrids, and
  • provided excellent control of southwestern corn borer.
• This article will discuss these studies to determine the value of Pioneer hybrids with the Yieldgard gene.

Pioneer brand hybrids with the Yieldgard® (YG) gene have proven extremely effective in resisting feeding damage by corn borer larvae. The yield advantage for resistant hybrids has varied by level of corn borer infestation. Under high insect pressure, yield advantages of 20 bu/acre are not uncommon. Under low insect pressure, the advantage is considerably lower, but has usually been more than sufficient to offset additional seed costs. Decisions regarding Bt technology for 2001 should be based on long-term average corn borer levels, and the expected yield advantages for Bt hybrids at these levels.

Corn borer pressure varies widely due to geography and weather (see map at right). Because of this variation, Pioneer has conducted studies to evaluate its hybrids under different levels of corn borer pressure. This Crop Insights will report on the results of these studies, and the value they demonstrate for Pioneer hybrids with the Yieldgard gene. This information can help growers make knowledgeable decisions about the use of Bt technology.

A corn borer management study was conducted to determine the value of Pioneer corn hybrids containing the YieldGard gene under different levels of corn borer pressure.

Specifically, the trials addressed the following questions:

• How effective are Pioneer corn hybrids containing the YieldGard gene in controlling damage from corn borers?
• What is the yield advantage of resistant Pioneer corn hybrids under various levels of corn borer infestation.

Split stalk from non-Bt corn plant showing European corn borer entry port (left) and larva in tunnel (right).

Pioneer hybrids with the YieldGard gene and genetically similar Pioneer hybrids not containing the gene were planted in plots 17.5 feet long by 4 rows wide at 70 locations across the Corn Belt. Entries varied at each location to fit areas of adaptation.

Hybrids contained in comparison groups were as follows:

Pioneer with YieldGard - 31A13, 31B13, 32K62, 32P76, 33G27, 33H68, 33P67, 33R88, 33A14, 33V08, 33Y09, 34F80, 34G82, 34K78, 34T14, 34R06, 34R07, 34A03, 35R58, 35M02, 35N05, 36Y96, 36G32, 36K27, 36F30, 37R71, 38P06, 38B22, 38W36, 39F06, 39J69, and 39K73.

Genetically similar isolines - 31A12, 3223, 32K61, 32P75, 33G26, 33H67, 33P66, 33R87, 3394, 34E79, 34G81, 34K77, 3489, 35R57, 3563, 36Y95, 3752, 3751, 37M81, 38P05, 3893, 3970, 3905, and 39K72.

Plots were evaluated for corn borer damage by examining 10 consecutive plants in each plot. Ears from these plants were examined for ear feeding by ECB or corn earworm, presence of mold, and presence of ear shank tunneling. In addition, because stalk tunneling is the best single indicator of yield loss potential, stalks were split on these 10 plants and the number and total length of tunnels were recorded. Plots were harvested for yield, moisture and test weight measurements.

Grain Yield

The relationship between number of cavities and yield advantage of Pioneer hybrids with the YieldGard gene compared to genetically similar hybrids without the gene is depicted in Figure 1. These data indicate that over 70 locations and 3 years, Pioneer hybrids with the YieldGard gene gave a yield advantage of 8.7% for every corn borer cavity. This is higher than the "classic" corn borer loss estimates of 5% to 6% per borer, which have been used extensively in economic threshold formulas to determine whether to treat for corn borer.

Corn Borer Damage Ratings

Pioneer hybrids with the YieldGard gene consistently provided protection from corn borers that was significantly better than non resistant hybrids under all infestation levels of European corn borer.

Figure 1. Percent yield advantage by number of corn borer
tunnels for resistant vs. non-resistant hybrids.

Additional Measurements

For all infestation levels, percent of ears with corn borer feeding, shank feeding, ear mold and inches of corn borer tunneling was significantly less in Pioneer hybrids with the YieldGard* gene than for genetically similar hybrids without the gene.

Corn Borer Damage Ratings

Pioneer hybrids with the Yieldgard gene have proven value, even at low levels of corn borer infestation. Figure 2 shows the additional income expected from Pioneer resistant hybrids at various levels of corn borer pressure.

Split ear shank from Bt plant shows no corn borer feeding.

In Figure 2, the value of Pioneer hybrids with the Yieldgard gene can be clearly seen. Even at a very low infestation level such as 0.5 borers/plant, these hybrids provide a positive economic return. Under moderate to severe pressure, these resistant hybrids can provide corn growers with 35 to 70 dollars of additional revenue per acre.

Level of Infestation (tunnels/plant)

Figure 2. Economics of using Pioneer resistant hybrids. Benefit is based on $2.00 corn, regression formula for % yield loss/borer (Y= -0.57 + 9.13X), and 150 bu/acre. Cost is the additional cost of hybrids with the YieldGard gene above that of non-Bt hybrids.

To determine the long-term expected value of resistant hybrids, it is necessary to know the average level of corn borer pressure by region. Minnesota routinely conducts a fall survey to determine the number of corn borers infesting a plant (Figure 3). Corn borer levels in many adjoining states are considered to be similar. The following conclusions can be drawn from this graph:

• Average ECB pressure is 1.1 borers/plant in Minnesota.
• Expected average yield advantage for Bt hybrids at this level of pressure is 10% (see Figure 1).
• Bt hybrids would at least return the additional cost of the seed almost every year.

Choosing the right Bt hybrid is critical for maximizing economic returns. In fact, the difference in performance among Bt hybrids is often greater than differences among non-resistant hybrids. Remember that the same rules of hybrid selection apply to all hybrids and technologies. Growers should review fall harvest data, then select a total value package that includes the Yieldgard gene, excellent yield for maturity, standability, disease resistance and other important traits.

Figure 3. European corn borer cycle for Minnesota.

Growers can also increase the value of Bt hybrids by placing them in fields most susceptible to corn borer damage (Hall, 1998). This includes:

• Early planted fields
• Late planted fields
• Fields with a history of high ECB damage
• Fields that are difficult to spray (terraces, point rows, oddly shaped fields, etc.)
• Fields that are harvested late
• Fields that are scouted less (e.g., a field far from home)

It is critically important to preserve the long-term effectiveness of this exciting new technology for corn insect management. Pioneer is committed to resistance management and has implemented a strategy for managing insect resistance that includes:

• Discovery of additional resistance genes
• Monitoring of ECB populations in the field
• Promoting refuges for ECB populations
• Developing education programs
• Responding quickly to unexpected damage complaints

For more information on resistance management, see Crop Insights 9 (20), Maintaining Bt Effectiveness Through Resistance Management (Butzen, S. 1999), or North Central Regional Publication 602, Bt corn and European corn borer (Ostlie et al. 1997). Additionally, all producers who purchase hybrids containing the YieldGard gene will be provided with information discussing resistance management strategies.

Hall, T.E. 1998. Value of Pioneer hybrids with the Yieldgard gene. Pioneer Hi-Bred Int'l. Inc., Johnston, Iowa.

Ostlie, K.R., W.D. Hutchison and R.L. Hellmich. 1997. Bt corn and European corn borer. NCR publication 602. University of Minnesota, St. Paul, MN. http://www.extension.umn.edu/distribution/cropsystems/DC7055.html

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