Preplant weed control in a ridge-till soybean (Glycine max) and grain sorghum (Sorghum bicolor) rotation.

Research in Kansas from 1983 to 1986 evaluated early preplant (30 to 45 days) and late preplant (10 to 14 days) herbicide treatments for weed control before ridge-till planting in a soybean and sorghum rotation. Control of fall panicum and common lambsquarters at planting time averaged at least 95% for all early preplant and 92% for late preplant treatments. Where no preplant treatnent was used, heavy weed growth in spring delayed soil dry-down, which resulted in poor ridge-till planting conditions and reduced plant stands, and ultimately reduced sorghum grain yields by 24% and soybean yields by 12%. Horsenettle population declined significantly, and honeyvine milkweed population increased. Smooth groundcherry populations fluctuated from year to year with no overall change. Nomenclature: Common lambsquarters, Chenopodium album L. #3 CHEAL; fall panicum, Panicum dichotonuflorum Michx. # PANDI; honeyvine milkweed, Ampelamus albidus (Nutt.)Britt # AMPAL; horsenettle, Solanum carolinense L. # SOLCA; smooth groundcherry, Solanum subglabrata Mackenz. & Bush # PHYSU; sorghum, Sorghum bicolor (L.)Moench.; soybean, Glycine max (L.)Merr. Additional index words: Conservation illage, crop rotations, sustainable agriculture, ataine, cyanazine, glyphosate, metolachlor, metribuzin, pendimethalin, 2,4-D, AMPAL, CHEAL, PANDI, PHYSU, SOLCA.