Bt toxin is an insecticide and insecticides allow protection of the crop only when insect pests are present at above threshold levels. If the pests fail to occur in damaging levels there will be a negative return of investment, from the extra cost paid for Bt corn seed. However, field trials conducted in 1996 and 1997 in northeastern NC indicated that yield increase was the exception, not the rule. European corn borer and southern cornstalk borer populations vary greatly between years and across the landscape. Due to this high variation, the probability of a return on investment, and the magnitude of return, is also variable.
Some corn growing areas of the state have a much higher probability of return.
Typically corn borers are most likely in the Tidewater region and in potato growing areas. The farmer's experience will be valuable in determining the likelihood of getting benefit from Bt corn. The economic magnitude of a more consistent production depends upon the frequency and magnitude of pest attack and the cost of Bt corn. Farmers should evaluate Bt corn under their specific conditions. Having a yield monitor available will greatly facilitate evaluating the benefit of Bt corn on a farm.