Effect of delayed glyphosate applications on weed control and soybean yield in late planted soybean

摘要

This study was designed to evaluate the effects of delayed glyphosateapplications on weed control and soybean yield in late planted soybean. The study was conducted on a Ebbertsilt loam with 1.5% organic matter and pH 6.7 at the Belleville Research Center. Fertilizer applied in 2003 was50 and 150 lb/A P2O5 and K2O, respectively, to an area that had been cropped to field corn in 2002. Asgrowbrand ‘AG 4403' glyphosate-resistant soybean was planted 1.0 inch deep at 75 lb/A into a reduced-till seedbedon June 21. Plots consisted of four rows with 30 inch row spacing, 28 ft long arranged in a randomizedcomplete block design with three replications. Application timings were preemergence (PRE) andpostemergence, based on weed height in inches (“W) or weed regrowth height in inches (“RG) and are listedbelow. The herbicides were broadcast applied with a CO2 pressurized sprayer using 8002 flat fan tips at 40 PSIin 20 GPA water. Monthly rainfall in inches was 2.8, 4.8, 8.3, 1.9 and 4.2 in April, May, June, July and August,respectively. Weed population per 0.25 m2 in the nontreated plots, mid-season, was 21 velvetleaf, 4 commonwaterhemp, 2 ivyleaf morningglory, 4 yellow nutsedge, 2 Palmer amaranth, 21 giant foxtail and 3 commoncocklebur.