In the greenhouse, naptalam at 1.1 to 4.5 kg ai ha−1 antagonized activity of paraquat at 0.04 to 0.14 kg ai ha−1 in 14 of 16 rate combinations when applied to sicklepod. Sicklepod shoot fresh weight reduction was less compared to that obtained with paraquat alone when paraquat at 0.04 kg ha−1 was mixed with bentazon at 0.42 to 0.84 kg ai ha−1 or monocarbamide dihydrogensulfate at 14 to 58 kg ai ha−1. Paraquat activity on Florida beggarweed was antagonized by mixtures of paraquat at 0.04 or 0.07 kg ha−1 with bentazon at 0.63 or 0.84 kg ha−1 or paraquat at 0.04 to 0.14 kg ha−1 with naptalam at 3.4 or 4.5 kg ha−1. Mixtures of lactofen at 0.06 to 0.22 kg ai ha−1 with monocarbamide dihydrogensulfate at 14 kg ha−1 or lactofen at 0.06 or 0.16 kg ha−1 with alachlor at 1.4 to 2.8 kg ai ha−1 synergistically increased tall morningglory shoot fresh weight reduction. In the field, excellent sicklepod shoot fresh weight reduction by paraquat applied alone masked most antagonistic effects of paraquat mixtures. Addition of alachlor to monocarbamide dihydrogensulfate at 29 kg ha−1 improved activity on sicklepod compared to monocarbamide dihydrogensulfate applied alone.