Weed management strategies in conventional- and reduced-tillage cotton production systems

Laboratory and greenhouse studies were conducted to determine the effect of temperature, solution pH, water stress, and planting depth on cutleaf eveningprimrose (Oenothera laciniata Hill) germination. Field studies were conducted to measure growth parameters of cutleaf eveningprimrose throughout the fall season. When treated with constant temperature, the optimum germination of cutleaf eveningprimrose occurred at 24 C. Onset, rate, and total germination were greatest in an alternating 20/35 C temperature regime. Germination decreased without increased solution pH and increased water stress. Emergence was optimum when seeds were buried at depths of 0.5 cm. Cutleaf eveningprimrose control was maximized when 2, 4-D was applied in mixture with glyphosate or paraquat.;Five studies were conducted at Clayton, Rocky Mount, and Lewiston-Woodville, NC, in 2001 and 2002, to evaluate weed management, crop tolerance, and yield in strip- and conventional-tillage glyphosate-resistant (GR) cotton. Addition of S-metolachlor to glyphosate formulations increased control of broadleaf signalgrass, goosegrass, large crabgrass, and yellow foxtail 14 to 43% compared to control with glyphosate alone. S-metolachlor was not beneficial for late-season control of entireleaf morningglory, jimsonweed, pitted morningglory, or yellow nutsedge. Addition of S-metolachlor to glyphosate formulations increased control of common lambsquarters, common ragweed, Palmer amaranth, smooth pigweed, and velvetleaf 6 to 46%. Addition of a late postemergence-directed spray (LAYBY) treatment of prometryn plus MSMA increased control to greater than 95% for all weeds regardless of early-postemergence (EPOST) treatment, and control was similar with or without S-metolachlor EPOST. Cotton lint yield was increased 220 kg/ha with the addition of S-metolachlor to glyphosate formulations compared to yield from glyphosate alone. Addition of LAYBY treatments increased yields 250 and 380 kg/ha for glyphosate plus S-metolachlor and glyphosate systems, respectively.;Field studies were conducted in five states at six locations from 2002 through 2003 to evaluate weed control and cotton response to early-postemergence (EPOST), postemergence (POST)/POST-directed spray (PDS), and late postemergence-directed (LAYBY) systems utilizing glyphosate-DIA (diammonium salt), S-metolachlor, trifloxysulfuron-sodium, prometryn, and MSMA. Annual broadleaf and grass control was increased with the addition of S-metolachlor to glyphosate-DIA EPOST systems (85 to 98% control) compared with glyphosate-DIA EPOST alone (65 to 91% control), except for sicklepod control where equivalent control was observed. Annual grass control was greater with glyphosate-DIA plus trifloxysulfuron-sodium PDS than with trifloxysulfuron-sodium postemergence (POST) or PDS or trifloxysulfuron-sodium plus MSMA PDS (90 to 94% vs. 75 to 83% control). With few exceptions, broadleaf weed control was equivalent for trifloxysulfuron-sodium applied POST alone, PDS alone, or in combination with glyphosate-DIA PDS or MSMA PDS herbicide treatments (81 to 99% control). Cotton lint yield increased 420 kg/ha with the addition of S-metolachlor to glyphosate-DIA EPOST treatments compared to systems without S-metolachlor EPOST. Cotton lint yield was increased 330 to 910 kg/ha with the addition of a POST herbicide treatment compared to systems without a POST/PDS treatment. Addition of a LAYBY herbicide treatment increased cotton lint yield by 440 kg/ha compared to systems without a LAYBY.;Studies were conducted at three locations in North Carolina in 2004 to evaluate density-dependent effects of glufosinate-resistant (GUR) corn on GUR cotton growth and lint yield. A GUR corn density of 5.25 plant/m of crop row reduced late season cotton height by 38, 43, and 43% at Clayton, Lewiston-Woodville, and Rocky Mount, respectively, compared to weed-free cotton height. GUR corn dry biomass per m crop row and GUR corn seed biomass per m of crop row decreased linearly with increasing GUR corn density at all locations. Percent GUR cotton lint yield loss increased 4, 5, and 8 percentage points at Clayton, Lewiston-Woodville, and Rocky Mount, respectively, with each 500 g increase in weed biomass per m of crop row.