Plant Population Response to European Corn Borer Infestation

• Pioneer evaluated Bt and non-Bt corn hybrid response to the combined effects of plant population and European corn borer (ECB) at 39 locations across North America in 2002.
• For non-Bt hybrids, as ECB infestation increased, yield response to plant population decreased, resulting in a reduction of the optimum population.
• For non-Bt hybrids, maximum yield potential could not be reached when ECB infestations were moderate to high.
• The yield advantage of Bt hybrids over non-Bt hybrids increased as both ECB infestation and plant population increased.

Pioneer Hi-Bred researchers conduct plant population studies each year in many locations and diverse growing environments across North America. Results of this research have shown that modern hybrids have improved tolerance to drought and density stress, allowing them to be planted at higher populations for higher yields. As a result of these hybrid improvements, corn planting rates in farmers' fields have steadily increased over time. In 2002, approximately 40% of North American corn acres had planting rates greater that 30,000 plants/A (1995-2002 Pioneer Brand Concentration Survey). Researchers and farmers alike have now proven that the ultimate genetic potential of modern corn hybrids can be best realized at high plant populations.

European Corn Borer (ECB) is one of the most significant corn pests in North America, reducing yields by tunneling into corn stalks and ears. Pioneer® brand hybrids with the Herculex¹ I (HXI) insect protection gene or YieldGard² Corn Borer (YGCB) gene provide excellent efficacy against ECB feeding. Research results in 2002 indicated that Pioneer hybrids with the HXI gene gave the same level of protection against ECB as did Pioneer hybrids with the YGCB gene.

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Non-Bt corn stalks damaged by ECB larvae. ECB
tunneling disrupts nutrient and water transport and
provides an entry port for stalk rot organisms.

The effects of plant population and of ECB have been evaluated independently in prior research studies. In 2002, Pioneer evaluated hybrid response to the combined effects of plant population and ECB infestation at 39 locations across North America. While drought was common across much of the Northern Corn Belt in 2002, ECB was found to be a significant yield-limiting factor at several research locations. This Crop Insights will report on research studies to evaluate Bt and non-Bt hybrid yield response to plant population at various levels of ECB infestation.

Non-Bt corn stalks damaged by ECB larvae. ECB tunneling disrupts nutrient and water transport and provides an entry port for stalk rot organisms.

In 2002, corn plant population response was evaluated in replicated small plot trials across North America. All locations were planted to achieve plant populations of 18,000, 24,000, 30,000, 36,000 and 42,000 plants/A. European corn borer infestations were determined prior to harvest at each location and categorized as low (<30%), moderate (30-60%) and high (>60%) based on visual observations. Optimum plant populations for highest grain yield were predicted using a quadratic model. Environmental characterization data were recorded at each research location to accurately access factors affecting crop growth and development.

Plant Population Response to European Corn Borer

Hybrid response to various levels of ECB infestation was evaluated in 2002. At 26 research locations, three non-Bt Pioneer hybrids of similar maturity (34M94, 34B97 and 34N43) were included in the evaluation. As ECB infestation increased in this study, corn grain yield response to increasing plant population decreased. This resulted in a reduction in yield potential and the optimum plant population (Figure 1 below).

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Figure 1. Grain yield response to plant
population for non-Bt corn hybrids at various
levels of ECB infestation.

Highest yields occurred when ECB infestation was lowest, and maximum yield potential could not be reached with moderate to high infestations of ECB. When ECB infestation was low, higher corn yield was achieved as population increased. Optimum plant populations for low, moderate and high ECB infestations were 39,000, 34,000 and 33,000 plants/A, respectively.

Bt and Non-Bt Hybrid Population Response to European Corn Borer

A plant population response comparison was made at 26 research locations between hybrids with either the YGCB or Herculex I gene versus the same base genetics without the genes. Selections for this comparison included Pioneer non-Bt hybrids 34M94, 34B97 and 34N43, Pioneer hybrids with the YGCB gene 34M95, 34B98 and 34N44, and Pioneer hybrids with the Herculex I gene 34M93 and 34B99. In the presence of low ECB pressure, corn plant population response was similar for Bt and non-Bt hybrids

(Figure 2 below).

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Figure 2. Grain yield response to plant
population for Bt and non-Bt corn hybrids at
a low level of ECB infestation.

At moderate and high ECB pressure, the Bt hybrids consistently produced more grain at all plant populations (Figures 3 and 4 below). Differences between Bt and non-Bt hybrid grain yield response increased as both ECB infestation and plant population increased.

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Figure 3. Grain yield response to plant
population for Bt and non-Bt corn hybrids at
a moderate level of ECB infestation.

Review a larger image (Figure 4).



Figure 4. Grain yield response to plant
population for Bt and non-Bt corn hybrids
at a high level of ECB infestation.

1995-2002 Brand Concentration Survey, Marketing Research and Analysis, Pioneer Hi-Bred Int'l, Inc.