This is from U of NE site....just so western guys don't feel left out:

A. IRM for Bt corn hybrids active against corn rootworm

1. Growers must plant a structured refuge of at least 20% non-Bt rootworm corn that may be treated with insecticides (e.g., seed treatments, liquid or granular) as needed to control corn rootworm larvae.
2. Growers will not be permitted to apply corn rootworm labeled insecticides to the refuge for control of insect pests (either rootworm beetles or other insects, e.g., western bean cutworms, grasshoppers, etc.) while adult corn rootworm are present unless the Bt rootworm field is treated in a similar manner.
3. Refuge plantings may be blocks in or adjacent to Bt rootworm cornfields or as in-field strips.
4. External refuges must be planted adjacent to Bt rootworm fields.
5. When planting the refuge in strips across a field, refuges must be at least six rows wide for YieldGard Rootworm and YieldGard Plus or at least four rows wide for Herculex RW and Herculex Xtra. It is preferable to have wider strips, such as 12 consecutive row-wide strips.
6. Insecticides for control of corn rootworm larvae may be applied to the refuge area. In addition, the refuge must be planted in similar ground as the Bt corn for rootworm (e.g., YieldGard Rootworm, or Herculex RW), that is, if the Bt corn for rootworm is planted in ground that was in corn the previous year, so must the refuge. General management of the Bt corn for rootworm and the refuge should be similar, e.g., planting dates, irrigation, fertility programs

This was all taken from here:

http://cropwatch.unl.edu/archives/2006/crop6/refuges.htm