Efficacy of preemergence herbicides on three annual grass weeds in different soils

Pot experiments evaluated the efficacy of several preemergence herbicides on three annual grasses that are major problem weeds in most maize growing regions Herbicides evaluated included alachlor metolachlor dimethenamid two formulations of acetochlor and proprietary mixes of acetochlor with atrazine or metribuzin Pots were filled with soil collected from the top 10 cm of seven maize (Zea mays) fields with different cropping histories and seeded with test grasses Herbicides were applied immediately after sowing with a precision glasshouse sprayer Additional seeds were sown at 2weekly intervals for 8 weeks Seedlings were counted 2 weeks after each planting Metolachlor was most effective in controlling summer grass (Digitaria sanguinalis) and rough bristle grass (Setaria verticillata) All herbicides were less effective against the large seeded broom corn millet (Panicum miliaceum) than the other grasses All the herbicides except metolachlor were less effective in soils with a long history of maize growing