Rice Weed Control with Penoxsulam (Grasp)

Two experiments were established in 2003 at the Rice Research and Extension Center near Stuttgart, Ark., to evaluate the potential of penoxsulam (Grasp) as part of a rice weed control program. In experiment one, penoxsulam applied alone and in tank mixtures early postemergence (EPOST) (two-leaf rice, one-leaf grass, two-leaf weeds) was evaluated, and experiment two evaluated penoxsulam applied alone and in tank mixtures mid-postemergence (MPOST) (four-leaf rice, threeto four-leaf grass, threeto four-leaf weeds). Plots were established in a randomized complete block design with four replications. Weeds evaluated were barnyardgrass (Echinochloa crus-galli), broadleaf signalgrass (Brachiaria platyphylla), hemp sesbania (Sesbania exaltata), northern jointvetch (Aeschynomene virginica), and pitted morningglory (Ipomoea lacunosa). In experiment one, yields ranged from 6357 to 7660 lb/acre, with rice treated with penoxsulam + propanil having a significantly higher yield than rice treated with penoxsulam alone, penoxsulam + clomazone, or propanil + quinclorac. In experiment two, rice yields ranged from 4571 to 7009 lb/acre, with treatments receiving MPOST applications having significantly higher yields than rice receiving only a PRE application. Penoxsulam applied postemergence appears to provide excellent barnyardgrass control and poor to moderate broadleaf weed control. Penoxsulam + cyhalofop-butyl did not result in reduced grass weed control.