Planting strategies for Bt rootworm corn refuge areas
Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.
Farmers planting Bt rootworm corn (YieldGuard Rootworm and Herculex RW) in 2006 are required to plant a refuge area within each field or in an adjacent field. The refuge area should be planted to non-Bt corn and cover at least 20% of the acreage in the field. The purpose of the refuge area is to prevent or significantly delay rootworm resistance to Bt. Some rootworm larvae will survive after feeding on the roots of Bt rootworm corn. The best way to keep the population of these resistant rootworm beetles low is to increase the odds that resistant beetles will mate with susceptible beetles. The refuge area is important as it ensures that a large population of susceptible beetles will be present to mate with the few resistant beetles in each field.
Research conducted at Purdue University indicates that a refuge area created by splitting the planter supplies twice as many susceptible beetles as a refuge planted as a single block. The refuge strips must be at least 6 rows wide. If you operate a 12-row planter, you can achieve a 25% refuge by simply dedicating the last three planter units on one end of the planter to non-Bt corn. If you operate a six-row planter you can achieve a 25% refuge by dedicating half of the planter to non-Bt corn and strip-plant half of the field.
The non-Bt hybrid planted in the refuge area must have a similar relative maturity rating as the Bt hybrid. The refuge area should be planted at the same time and managed in the same manner as the Bt field or area. Matching the hybrid maturity and the planting date will ensure that the corn rootworm larvae in the field and the refuge area will develop at the same rates and emerge as adults at the same time. If an adjacent field is used for the refuge, it must be owned or managed by the same grower. A ditch or road can separate the refuge area from the Bt field. Always protect the non-Bt corn in the refuge area with treated seed or soil insecticides at planting.