As mentioned in previous issues of the Bulletin and again now, first-generation European corn borer larvae are presently active in many cornfields throughout Illinois. Scouting for first-generation larvae and injury should have begun several weeks ago for most areas in the state, especially in the southern half of Illinois. The statewide progress of corn planting was quite good this year, except for many rain-soaked areas of southern Illinois. A recently published paper proves clearly that planting date can significantly influence the return on the investment of a Bt hybrid purchased for European corn borer protection.
The influence of planting date on the economics of Bt corn utilization for European corn borer management was recently discussed in a journal article (Journal of Economic Entomology, June 2003 issue) by Clint Pilcher and Marlin Rice, Department of Entomology at Iowa State University. The title of their paper is "Economic Analysis of Planting Dates to Manage European Corn Borer (Lepidoptera: Crambidae) with Bt Corn." Their research was conducted from 1996 through 1998 in three Iowa locations (Ames, central Iowa; Lewis, southwestern Iowa; Nashua, northeastern Iowa). They evaluated the interactions of planting date for two Bt events designed to provide European corn borer control: event 176 (no longer commercialized) and event Bt11, Cry1A(b), Northrup King/Syngenta Seeds. This article summarizes the results only for the Bt11 event.
In 1996, N6800Bt and N6800 (non-Bt near isoline) hybrids were planted near Ames, Lewis, and Nashua, Iowa. In 1997 and 1998, N7333Bt and N7333 (non-Bt near isoline) hybrids were planted near Ames and Lewis. At the Nashua location, N4640Bt and N4640 (non-Bt near isoline) hybrids were planted in 1997 and 1998. The hybrids planted in Ames and Lewis required 110 to 112 days to reach maturity. In Nashua, 102- to 106-day hybrids were utilized. A split-plot design was used for the experiment, with Bt or non-Bt (near isolines) serving as the whole plots. Three planting date targets (early, April 20-30; middle, May 1-10; late, May 11-20) served as the split-plot treatments. All treatments were replicated four times at each location. Individual plots were 24 rows wide (30-inch rows) and varied in length from approximately 60 to 90 feet. Seeding rates ranged from 27,680 to 28,770 per acre. Event Bt11 provided 100% control of first- and second-generation European corn borers for all three planting dates. The middle six or eight rows were machine harvested at physiological maturity.
A Bt premium of $10.00 per acre was used for Pilcher and Rice's economic analyses. The authors compared yields of the Bt (Bt11 event) and non-Bt (near isoline) hybrids and estimated overall profits (above and beyond the cost of the Bt premium) according to the following planting dates: early planting date$3.74 per acre; middle planting date$7.85 per acre; late planting date$16.90 per acre. The investigators observed that approximately a third of the moisture levels in Bt corn were greater than in non-Bt corn at harvest. They speculated that increased stalk tunneling from European corn borer larvae in non-Bt corn led to more rapid drying of stalks and ultimately of the grain. They offered the following remarks with respect to the feasibility of recommending planting dates for Bt hybrids to maximize profits: "Consistently recommending when during the planting sequence a grower should plant Bt corn to realize the greatest benefit is impossible; however, results from this study suggest that planting Bt corn late during the spring planting sequence provides the greatest opportunity for economic benefit."
Readers are encouraged to obtain reprints of the full article by contacting the authors. Specific data for losses and profits (dollars per acre) are provided for each year by location by planting date combination. Results from this research clearly highlight the value of Bt corn for European corn borer management, especially in late-planted fields.--Mike Gray