ALS-Inhibiting Herbicides on Germination and Seedling Growth in Two Cultivars of Switchgrass.

ALS-Inhibiting Herbicides on Germination and Seedling Growth in Two Cultivars of Switchgrass

Calyn M. Adams¹, Jesse I. Morrison¹, Brian S. Baldwin¹

¹Department of Plant and Soil Sciences, Mississippi State University; Starkville, MS

Abstract

Switchgrass (Panicum virgatum L.) is a perennial warm-season native grass that is a cornerstone species in conservation systems and can also be utilized as a high-quality forage. ‘Tusca’ is a cultivar of lowland switchgrass selected from ‘Alamo’ (USDA NRCS, Knox City, TX) for tolerance to the herbicide imazapic. This study was conducted to determine if selection breeding conferred cross-protection to similar ALS-inhibiting herbicides in Tusca. Five ALS-inhibiting herbicides, including imazapic (IPIC), imazamox (IMOX), imazapyr (IPYR), imazethapyr (ITHR), and metsulfuron methyl (MSUL), were tested on both switchgrass cultivars and wild-type johnsongrass [Sorghum halepense (L) Pers.] at five rates (25, 50, 75, 100, and 125% of the label rate) plus an untreated control, under laboratory and greenhouse conditions. Johnsongrass was used as a reference species to confirm efficacy of herbicide treatments. Six replications of 25 seed of both cultivars and johnsongrass were screened for response to herbicide treatment at germination as well as the 3-leaf stage. Mean germination percentage for untreated Tusca, Alamo, and johnsongrass were 71.5, 24.8, and 40.8, respectively. Compared to controls, mean germination percentage of Tusca remained >50% at all rates of ITHR and IMOX, whereas ITHR decreased germination of Alamo to <25% and IMOX to <50%. While Tusca shows some improved tolerance to IPIC at germination, greater tolerance was found to ITHR, IPYR, and IMOX,whereas mean germination percentage of Alamo was significantly reduced by all treatments.