Many field sizes and configurations will make the ‘whole field’ option impossible and require that a specific block or portion of a field be planted as non-Bt refuge. One potential problem in this arrangement is the possibility of having the 5% non-Bt refuge too far away for rootworm adults to mate with those emerging from the Bt planted area.
This is considered the best and most effective option for this type of Bt hybrid. It carries the 5% refuge deeper into the field, helping enable rootworm adults emerging from the Bt hybrid area to mate with those emerging from the refuge strips. This approach eliminates the need to dump planter boxes and switch hybrids over the course of a field or farm, but it is restricted to planters with individual row hoppers. Each refuge strip must be a MINIMUM OF TWO ROWS wide. DO NOT plant less than two rows of refuge and DO NOT mix Bt and non-Bt seed on-farm. This could allow the larva to travel and feed on both Bt and non-Bt hybrid, thus ingesting an insufficient amount of Bt-toxin and increasing the risk of resistance development
Planting headland areas with non-Bt hybrids is another option. Some quick calculations indicate that depending on the dimensions of the field, headlands of 6 to 8 rows in width can generally meet the 5 per cent requirement on fields up to approximately 60 acres (again, depending on shape).