Broadleaf signalgrass control from preemergence (PRE) herbicides was usually lower in no-till than in tilled plots. Broadleaf signalgrass control was most nearly complete in tilled plots treated with metolachlor in 1995, a year that favored an herbicide with more soil persistence. Broadleaf signalgrass control was most nearly complete in tilled plots treated with acetochlor in 1996, a year in which rainfall to activate the herbicides did not occur until 9 d after planting. The 1996 data indicated that acetochlor was more stable on the soil surface under the drier conditions. There was no difference in broadleaf signalgrass control between the two acetochlor formulations. Alachlor, metolachlor, and dimethenamid controlled broadleaf signalgrass > 80% for about 4 wk, acetochlor provided control for about 4 wk under no-till conditions and about 8 wk in tilled plots, and pendimethalin provided about 2 wk broadleaf signalgrass control. Acetochlor provided consistent control regardless of the rainfall pattern after application.
