Studies were conducted in 2003 and 2004 to determine the effects of application timing and rate of halosulfuron on sweet potato (Ipomoea batatas) yield and quality. Halosulfuron was applied at 1, 2, and 4 weeks after transplanting (WAP) sweet potato in 2003, and 2, 3, and 4 WAP in 2004. Treatments within each timing included halosulfuron at 13, 26, 39, 52, and 65 g a.i./ha plus a weed-free control. Combined over year, site, cultivar and rate, halosulfuron applied at 1, 2, 3, and 4 WAP stunted sweet potato by 32, 15, 11, and 14, respectively, at 2 weeks 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 decrease the yield of No. 1 roots. The total yield was decreased by ~11 at 1, 2, and 3 WAP application timings. Halosulfuron at 4 WAP did not decrease the total yield. Combined over year, site, and cultivar, halosulfuron applied at 39 g/ha did not decrease the weight of No. 1 roots or total crop yield and thus could be an effective POST option for weed control in sweet potato.
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