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. 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
Producers with six-row planters can dedicate four rows of the planter to Bt and two rows to non-Bt. However, this method results in a 33 per cent refuge size, so it may not be the best option in areas with high pest pressure where it is advantageous to plant as much Bt corn as possible.
Eight and Twelve-Row Planters
Planting alternating strips is an option best suited to growers with eight or twelve-row planters. Dedicating two end row units to non-Bt refuge hybrids will effectively result in 25 per cent (eight-row planter) and 17 per cent (12-row planter) of corn acreage as refuge. This more intimate pairing of hybrids require additional care in selecting refuge hybrids that will be compatible with your Bt hybrid in terms of maturity, resistance to lodging, etc.
Planting headland areas with non-Bt hybrids is another option. Some quick calculations indicate that depending on the dimensions of the field, headlands of 24 to 30 rows in width can generally meet the 20 per cent requirement on fields up to approximately 60 acres (again, depending on shape).
Adjacent means that the refuge must be planted in the field immediately beside the Bt field and can be separated by no more than a two lane road, path, or ditch. It can not be separated by an entire field, woodlot, river or major highway.