This study was designed to evaluate weed control and weed population shifts over a long period of time in transgenic crops. The study was conducted on an Ebbert silt loam with 1.5 percent organic matter and pH 6.7 at the Belleville Research Center beginning in 1998. The study has been in a corn/soybean rotation beginning with corn in 1998. Fertilizer applied in 2002 was 150, 50 and 150 lb/A N, P_2O_5 and K_2O, respectively, to an area that had been cropped to soybean in 2001. Pioneer brand '33P69LL' glufosinate-resistant field corn was planted 1.5 inch deep at 28 000 seed/A on June 2. Plots consisted of four rows with 30 inch row spacing, 27 ft long arranged in a split-plot design with 4 replications. Main plots were either no-till or tilled and sub-plots were herbicide treatment. The herbicides were broadcast applied with a CO_2 pressurized sprayer using 8003 flat fan tips at 40 PSI in 20 GPA water. Application timings were preemergence (PRE), 2 to 4 inch weeds POST only or following a PRE thatdid not include atrazine (2-4"W-1), 2 to 4 inch weeds following a PRE application that included atrazine (2-4"W-2) and 10 days after a 2-4"W-1 application (10DA2-4"). Monthly rainfall in inches in 2002 was 4.9, 6.6, 1.7, 3.7 and 3.6 in April, May, June,July and August, respectively. Weed population per 0.25 m~2 in the nontreated plots, at no-till burndown in 2002, was 11 little barley, 6 common ragweed, 1 giant foxtail, 1 yellow nutsedge, and 1 common cocklebur. Weed population per 0.25 m~2 in the nontreated plots, midseason in 2002, was 8 common ragweed, 45 giant foxtail, 1 yellow nutsedge, and <1 common cocklebur, ivyleaf morningglory, velvetleaf and common waterhemp.
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