Thirteen field trials were conducted in 1999 and 2000 to evaluate postemergence (POST) weed control with single applications of bromoxynil at 420 or 560 g ai/ha, glufosinate at 291 or 409 g ai/ha, glyphosate at 1,120 g ai/ha, pyrithiobac at 36 or 72 g ai/ha, or sulfosate at 1,120 g ai/ha. Additional treatments evaluated included two applications with glufosinate at both rates in all possible combinations, two applications of glyphosate, and two applications of sulfosate. Weeds were 2 to 5 cm or 8 to 10 cm tall for annual grass and broadleaf weeds whereas yellow nutsedge and glyphosate-resistant corn were 8 to 10 cm tall. All herbicide treatments controlled 2- to 5-cm common cocklebur, Florida beggarweed, jimsonweed, ladysthumb smartweed, Pennsylvania smartweed, pitted morningglory, prickly sida, redroot pigweed, smooth pigweed, and velvetleaf at least 90%. All herbicide treatments except pyrithiobac at either rate controlled 2- to 5-cm common lambsquarters, common ragweed, and tall morningglory at least 90%; pyrithiobac at the lower rate was the only treatment that failed to control entireleaf and ivyleaf morningglory at least 90%. Bromoxynil and pyrithiobac at either rate controlled 2- to 5-cm sicklepod 33 to 68% whereas glufosinate, glyphosate, and sulfostate controlled ≥99%. Glyphosate and sulfosate applied once or twice controlled hemp sesbania less than 70% and volunteer peanut less than 80%. Bromoxynil and pyrithiobac were the least effective treatments for control of annual grass species and bromoxynil controlled Palmer amaranth less than 80%. Glufosinate controlled broadleaf signalgrass, fall panicum, giant foxtail, green foxtail, large crabgrass, yellow foxtail, seedling johnsongrass, Texas panicum, and glyphosate-resistant corn at least 90% but controlled goosegrass less than 60%. Glyphosate and sulfosate controlled all grass species except glyphosate-resistant corn at least 90%. In greenhouse research, goosegrass could be controlled with glufosinate POST plus a late POST-directed treatment of prometryn plus monosodium salt of methylarsonic acid.

Because of a previously reported antagonism of clethodim activity by other herbicides, greenhouse experiments were conducted to determine goosegrass control with clethodim and glufosinate postemergence alone, in tank mixtures, and as sequential treatments. Herbicide treatments consisted of glufosinate at 0, 290, or 410 g ai/ha and clethodim at 0, 105, or 140 g ai/ha, each applied alone, in all possible combinations of the above application rates, or sequentially. Glufosinate at either rate alone controlled goosegrass at the two- to four-leaf growth stage <44%, and control was less for goosegrass at the one- to two- and four- to six-tiller growth stages. Clethodim controlled two- to four-leaf and one- to two-tiller goosegrass 91 and 99% at application rates of 105 and 140 g/ha, respectively, and controlled four- to six-tiller goosegrass 68 and 83% at application rates of 105 and 140 g ai/ha, respectively. All tank mixtures of glufosinate with clethodim reduced goosegrass control at least 52 percentage points when compared to the control with clethodim alone. Glufosinate at 290 or 410 g/ha when applied sequentially 7 or 14 d prior to clethodim reduced goosegrass control at least 50 percentage points compared to the control obtained with clethodim applied alone. Clethodim at rates of 105 or 140 g/ha when applied 7 or 14 d prior to glufosinate controlled goosegrass equivalent to the control obtained with each respective rate of clethodim applied alone at the two- to four-leaf and one- to two-tiller growth stage. Clethodim should be applied to goosegrass no larger than at the one- to two-tiller growth stage at least 7 d prior to glufosinate application or 14 d after a glufosinate application for effective goosegrass control.

Field studies were conducted at two locations in North Carolina in 1999 and 2000 to evaluate weed and bromoxynil-resistant cotton response to bromoxynil, pyrithiobac, and MSMA applied early postemergence (EPOST), alone or mixtures in all combinations (two way and three way), and to prometryn plus MSMA applied late postemergence directed (LAYBY). Trifluralin preplant incorporated followed by fluometuron preemergence controlled common lambsquarters, eclipta, and smooth pigweed at least 90%. These herbicides also provided greater than 90% common ragweed control at two locations but only 65% control at a third location. Pyrithiobac and pyrithiobac plus MSMA EPOST increased sicklepod control more than did bromoxynil or bromoxynil plus MSMA EPOST. Bromoxynil and pyrithiobac were more effective for sicklepod control when applied in mixture with MSMA. Bromoxynil plus pyrithiobac EPOST or with MSMA controlled (≥ 90%) common lambsquarters, common ragweed, entireleaf morningglory, prickly sida, and smooth pigweed early season. But the LAYBY treatment of prometryn plus MSMA frequently improved late-season control of entireleaf morningglory, large crabgrass, prickly sida, and sicklepod. A tank mixture of MSMA plus bromoxynil or pyrithiobac and the three-component tank mixture (bromoyxnil, MSMA, plus pyrithiobac) provided a broader weed control spectrum than did either bromoxynil or pyrithiobac alone. Cotton lint yields were increased with all postemergence systems, and the LAYBY treatment of prometryn plus MSMA increased cotton yields in 13 out of 16 comparisons. High cotton yields were indicative of high levels of weed control.