Field experiments were conducted to evaluate possible interactions of clethodim with imazapic applied as mixtures or sequentially for control of broadleaf signalgrass, fall panicum, goosegrass, and large crabgrass. Imazapic at 70 g ai/ha alone controlled grass weeds inconsistently, whereas clethodim at 140 g ai/ha alone controlled the same weeds at least 99%. Imazapic did not affect broadleaf signalgrass control by clethodim. Reduced control of fall panicum, goosegrass, and large crabgrass was observed when clethodim and imazapic were applied in mixture. Antagonism of clethodim occurred when clethodim was applied 1 d before or up to 3 d after application of imazapic (fall panicum and large crabgrass). Antagonism of goosegrass control was noted when imazapic was applied 3 d before or up to 7 d after application of clethodim. In other experiments, large crabgrass and Texas panicum control by clethodim (70 and 140 g/ha) applied alone or with imazapic (70 g/ ha) or bentazon (1.1 kg ai/ha) plus 2,4-DB (0.28 kg ai/ha) either with or without ammonium sulfate (2.8 kg/ha) was evaluated. Texas panicum control by clethodim was reduced by imazapic regardless of the ammonium sulfate rate. However, large crabgrass control by imazapic was not affected in these experiments. Control of both grasses by clethodim was reduced substantially by bentazon plus 2,4-DB, although in some instances ammonium sulfate improved control when in mixture. Ammonium sulfate improved control by clethodim in some instances irrespective of the broadleaf–sedge herbicide treatments.
Nomenclature: Bentazon; clethodim; 2,4-DB; imazapic; broadleaf signalgrass, Brachiaria platyphylla (Griseb) Nash #3 BRAPP; fall panicum, Panicum dichotomiflorum L. # PANDI; goosegrass, Eleusine indica L. Gaertn. # ELEIN; large crabgrass, Digitaria sanguinalis L. Scop. # DIGSA; Texas panicum, Panicum texanum Buckl. # PANTE.
Additional index words: Ammonium sulfate, antagonism, herbicide compatibility, herbicide interaction, sequential application.