Experiments were conducted from 1997 through 2001 in Georgia, Florida, North Carolina, and Texas to evaluate compatibility of selected postemergence herbicides and fungicides applied in tank mixtures. Control of broadleaf signalgrass [Brachiaria platyphylla (Griseb.) Nash], goosegrass [Eleusine indica (L.) Gaertn.], large crabgrass [Digitaria sanguinalis (L.) Scop.], and Texas panicum (Panicum texanum Buckl.) by clethodim applied in tank mixtures with copper-based fungicides, fungicides containing chlorothalonil, azoxystrobin, and iprodione was reduced in 80, 69, 60, and 46% of comparisons, respectively, when compared to clethodim alone. Fluazinam, tebuconazole, and propiconazole did not reduce efficacy of clethodim. Efficacy was reduced more by fungicides when clethodim was applied in 230 L/ha spray volume compared with 94 L/ha. Efficacy of acifluorfen, bentazon, imazethapyr, and 2,4-DB applied with fungicides was also compared. Smooth pigweed (Amaranthus hybridus L.) control by 2,4-DB was reduced in at least two of three experiments when applied with chlorothalonil, copper-based fungicides, tebuconazole, azoxystrobin, and fluazinam. Iprodione did not affect efficacy of 2,4-DB. Control of smooth pigweed by imazethapyr was reduced when applied in combination with copper-based fungicides but not when applied with chlorothalonil, propiconazole, tebuconazole, fluazinam, propiconazole plus flutolanil, or propiconazole plus trifloxystrobin. Smooth pigweed control by acifluorfen was reduced in one of three experiments when applied with tebuconazole. Efficacy of acifluorfen was not affected by chlorothalonil, azoxystrobin, propiconazole, or fluazinam. Yellow nutsedge (Cyperus esculentus L.) control by bentazon was reduced by propiconazole plus chlorothalonil, propiconazole plus flutolanil, and copper-based fungicides. With the exception of fluazinam and chlorothalonil applied with 2,4-DB in one experiment, fungicides did not affect peanut injury following application of acifluorfen, clethodim, imazethapyr, or 2,4-DB.