Field and greenhouse experiments were conducted to evaluate factors affecting johnsongrass [Sorghum halepense (L.) Pers. # SORHA] control in soybeans [Glycine max (L.) Merr. ‘Essex’] with three foliarly-applied herbicides. In 1980, johnsongrass height at treatment time had little effect on control due to inadequate soil moisture. In 1981, a wet year, best control was achieved on 15- or 40-cm-tall johnsongrass. BAS-9052 {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} at 0.6 kg/ha gave good to excellent control at all growth stages. Two applications of 0.3 kg/ha of BAS-9052 in both years and PP-009 butyl {2-[4-[5-(trifluoromethyl-2-pyridinyloxy)] phenoxy] propanoate} in 1981 increased johnsongrass control compared to only one treatment. Mixing BAS-9052 with other herbicides significantly reduced johnsongrass control. Greenhouse studies to determine the effect of soil water on herbicide response indicated that drier soils decreased johnsongrass regrowth with PP-009 and increased regrowth with BAS-9052.
