Studies were conducted in 2003 and 2004 to determine the effect of application timing and halosulfuron rate on sweetpotato yield and quality. Halosulfuron was applied 1, 2, and 4 wks after transplanting (WAP) sweetpotato in 2003, and 2, 3, and 4 WAP in 2004. Treatments within each timing included halosulfuron at 13, 26, 39, 52, and 65 g ai/ha plus a weed-free control. Combined over year, site, cultivar and rate, halosulfuron applied at 1, 2, 3, and 4 WAP stunted sweetpotato 32, 15, 11, and 14%, respectively, rated 2 wks after treatment. The stunting observed with the 1 and 2 WAP timings caused a 17 and 10% reduction in yield of No. 1 roots, respectively, compared with the weed-free control. The 3 and 4 WAP timings of halosulfuron did not reduce yield of No. 1 roots. Total yield was reduced approximately 11% at the 1, 2, and 3 WAP application timings. Halosulfuron at 4 WAP did not reduce total yield. Combined over year, site, and cultivar, halosulfuron applied at 39 g/ha did not reduce the weight of No. 1 roots or total crop yield and thus could be an effective POST option for weed control in sweetpotato.

Nomenclature: Halosulfuron; sweetpotato, Ipomoea batatas (L.) Lam.