LAUSR

BACKGROUND Annual bluegrass is a troublesome weed in managed turf systems. A survey was conducted to evaluate the prevalence of herbicide resistance in golf course populations of annual bluegrass in eastern Texas. Screenings were conducted for two photosystem II (PS II)-inhibitor herbicides [simazine preemergence (PRE), amicarbazone postemergence (POST)], two acetolactate synthase (ALS) inhibitors (foramsulfuron POST, trifloxysulfuron POST) and one microtubule assembly inhibitor (pronamide PRE/POST). RESULTS Ninety percent of the populations were found to be resistant to at least one of the tested herbicides. The TX15-14 population was >490, 178, 10, 26, 4.3, 3.8-fold, and the TX15-27 population was >490, 16, 28, 84, 5.2, 4.1-fold less sensitive to simazine, amicarbazone, foramsulfuron, trifloxysulfuron, pronamide POST and pronamide PRE, respectively, compared to the susceptible standard TX15-SUS. Populations resistant to pronamide POST were completely controlled by pronamide PRE at the label recommended rate. The ALS and psbA gene sequence analysis indicated the presence of target site mutations (Ser-264-Gly in the psbA gene of TX15-14 and Trp-574-Leu in the ALS gene of TX15-27). However, given the absence of any target-site mutation in the ALS gene of TX15-14, the psbA gene of TX15-27, and α-tubulin of both populations, non-target site mechanisms of resistance are suspected. CONCLUSION This is the first case of multiple herbicide-resistance in annual bluegrass populations to three herbicide modes of action. Results show the widespread occurrence of multiple herbicide-resistance in golf course annual bluegrass populations in eastern Texas and emphasize the need for the development and implementation of effective resistance management practices. This article is protected by copyright. All rights reserved.