Herbicide Programs in No-Tillage and Conventional-Tillage Soybeans (Glycine max) Double Cropped After Wheat (Triticum aestivum)

Abstract

Postemergence and commonly used preemergence plus postemergence herbicide programs were evaluated for weed control in conventional and no-tillage soybeans double cropped after winter wheat in the northern Mississippi River Delta. Broadleaf weed species present varied with tillage, location, and year. Large crabgrass was present in both tillage systems for all locations and years. Conventional tillage usually resulted in higher densities of large crabgrass, common cocklebur, and smooth pigweed. Soil-applied preemergence herbicides alone did not provide season-long ivyleaf and entireleaf morningglory or common cocklebur control in either tillage system. For weed control and soybean yields comparable to weed-free controls, postemergence broadleaf herbicides were required in both tillage systems following the soil-applied herbicide programs, alachlor plus linuron and alachlor plus metribuzin. Postemergence herbicide programs provided excellent season-long annual grass and broadleaf weed control when sethoxydim was applied separately from the broadleaf herbicides. Antagonism of large crabgrass control resulted when sethoxydim was tank mixed with postemergence broadleaf herbicides, compared to separate applications of the postemergence grass and broadleaf herbicides. In three out of four studies, soybean yields in handweeded controls were similar between tillage systems.