Confirmation of Shattercane (Sorghum bicolor) Resistance to ALS-Inhibiting Herbicides in Ohio

Abstract

A population of shattercane (Sorghum bicolor (L.) Moench) located in Fairfield County, Ohio, was investigated for herbicide resistance after it persisted in a field that had been treated repeatedly with herbicides that inhibit acetolactate synthase (ALS). Herbicide bioassays confirmed cross-resistance of the suspected resistant (R) population to the ALS inhibitors nicosulfuron, primisulfuron, and imazethapyr. Herbicide doses required to reduce R shattercane shoot dry weight 50% (i.e., the GR50 values) were > 35,000, > 40,000, and 34,215 g ai/ha for nicosulfuron, primisulfuron, and imazethapyr, respectively. In contrast, GR50 values for the same herbicides applied to a susceptible (S) shattercane population from an adjacent county were 0.185, 0.025, and 0.038 g/ha, respectively. The high levels of resistance exhibited by the R population suggest that the resistance mechanism is due to one or more alterations in ALS, the herbicide target site. Effective management of ALS herbicide-resistant shattercane will require an integrated strategy designed to isolate the R population and deplete its soil seed bank while minimizing herbicide selection pressure. Accepted for publication 14 October 2002. Published 21 October 2002.