As a condition of registration, the EPA requires Bt technology registrants to develop and execute resistance management plans. The acres of non-Bt hybrids produce a sufficient quantity of susceptible corn borer moths to mate with potentially resistant moths surviving from nearby Bt hybrids. The offspring resulting from the mating of susceptible and resistant corn borers should also be susceptible to the toxin expressed by Bt plants. This prevents the buildup of resistance.
Growers can choose the planting method that best fits their operation.
Hellmich says, in most cases, it's convenient to plant in blocks. Growers also may plant strips or border rows as refuge, but mixing the two types of seed is not recommended. Another key to establishing an effective refuge is hybrid selection, says Wandrey. The growth and development of the non-Bt and Bt hybrids should be similar, so the hybrids attract ECB moths at the same rate. The two hybrids should be comparable in maturity, early vigor and plant height.