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. This could result in the most effective refuge. One potential problem in this arrangement is the possibility of having a non-Bt hybrid "land locked" by the main Bt hybrid of the field at harvest.
Planting alternating strips of Bt and non-Bt hybrids can be an effective refuge. 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 FOUR ROWS wide. DO NOT plant less than four 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).