Evaluation of chemical control and seasonal application options for smutgrass (Sporobolus indicus)

Abstract

Smutgrass is a non-native perennial weed that is problematic because of its poor palatability to cattle and its difficulty to control once established. There is limited literature on the effectiveness of alternative labeled herbicides to hexazinone for smutgrass control and forage injury. This study aimed to evaluate seasonal applications of labeled forage herbicides for maximum smutgrass control. The second objective was to evaluate preemergent herbicides and hexazinone to control smutgrass germinating from seed. Hexazinone, nicosulfuron + metsulfuron-methyl, and glyphosate + imazapic were the most effective postemergence treatments, while quinclorac had little activity on smutgrass. Common bermudagrass forage fully recovered from all treatments by 3 months after treatment. Hexazinone, nicosulfuron + metsulfuron methyl, glyphosate, and imazapic were observed postemergence over spring, summer, and fall applications. Summer applications of hexazinone resulted in the highest level of control, while spring treatments provided the least control. Applications of hexazinone or glyphosate resulted in the most effective smutgrass control. However, fall applications resulted in the least forage injury. Results of the preemergent study indicate that treatments of indaziflam and hexazinone provide adequate control of germinating smutgrass seedlings in the greenhouse at 0.25, 0.5, and 0.75X of the lowest recommended labeled rate for seedling grass control. Indaziflam treatments prevented the emergence of any visible smutgrass seedling tissue, compared to hexazinone, which fully controlled the germinating seedlings by 21 DAT, or pendimethalin significantly reduced seedling numbers at the 0.5 and 0.75X rates.