The influence of temperature and relative humidity on the activity of acifluorfen, fomesafen, lactofen, and acifluorfen plus bentazon on prickly sida, pitted and entireleaf morningglory, and common cocklebur was evaluated in a growth chamber. Reduced control of all species was observed at 50% relative humidity as compared to 85% relative humidity when temperatures were higher (32/55 C day/night). Similar response to relative humidity was observed at the lower temperature (25/15 C) when treatments were applied 14 days after emergence (DAE). Changes in temperature at the same relative humidity did not alter herbicidal activity. Delaying application timing from 7 to 14 DAE decreased control by all herbicides except lactofen applied at high relative humidity, which controlled prickly sida at both 7 and 14 DAE.

The effects of 1.24 kg ha−1 ammonium sulfate, 5 g ae ha−1 of the isopropylamine salt of imazapyr, and air temperatures of 18, 27, or 35 C at 40 or 100% relative humidity (RH) on the absorption and translocation of the ammonium salt of 14C-imazethapyr applied postemergence to pitted morningglory were evaluated. Absorption of 14C-imazethapyr was greater at 100 than at 40% RH (88 vs. 47%). At 40% RH, absorption was increased to 79% by the addition of ammonium sulfate. At 100% RH absorption was similar with all treatments. Translocation of 14C-imazethapyr applied alone was greater at 100 than at 40% RH (34 vs. 17%). Addition of ammonium sulfate increased translocation at 40% RH but not at 100%. Addition of imazapyr did not affect 14C translocation. Distribution of 14C throughout the plant was more acropetal than basipetal with the greatest distribution at 35 C.

Field experiments were conducted to evaluate the influence of application timing of imazethapyr and fluazifop-P on rhizome johnsongrass and pitted morningglory control in soybean. Herbicides were applied at three timings keyed to johnsongrass heights of 15, 30, and 60 cm and 3-, 6-, and 9-leaf pitted morningglory. Evaluations 6 wk after the final treatment indicated imazethapyr controlled both species best when applied at the 15-cm johnsongrass growth stage. Increasing imazethapyr rate did not increase control of pitted morningglory, but did increase johnsongrass control at the 15-cm application timing. However, at the 30-cm johnsongrass application timing, increasing the rate from 0.07 to 0.10 kg ha-1 improved control of both species. Johnsongrass control with imazethapyr was no more than 64% when applications were delayed to 30-cm or larger johnsongrass. Fluazifop-P controlled johnsongrass well at all timings.

Field experiments were established in 1991 and 1992 on silty clay and sandy loam soils to evaluate various split rates of early PPI and PRE (to soybean) selective herbicides with and without paraquat for sicklepod and pitted morningglory control in stale seedbed soybean. Metribuzin at 360 g ai/ha plus 60 g ai/ha chlorimuron tank-mixed with 700 g ai/ha paraquat controlled sicklepod and pitted morningglory 83 and 91%, respectively, 4 wk after planting. Without paraquat, sicklepod and pitted morningglory control was only 65% and 67%, respectively. Imazaquin at 140 g/ha PRE tank-mixed with paraquat controlled sicklepod 78% and pitted morningglory 92%. Without paraquat, control was 38% and 84%, respectively. Early PPI applications of metribuzin plus chlorimuron or imazaquin at the full rate alone or followed by paraquat at planting resulted in poor control. With sequential treatments (PPI followed by PRE) the addition of paraquat at planting did not usually improve control, and either imazaquin or metribuzin plus chlorimuron provided equivalent control when compared with the full rate of either herbicide applied PRE. Season-long weed control was not obtained with any treatment in any experiment, and the crop was not harvestable.

Cultivation timings and postemergence applications of AC 263,222 were evaluated for sicklepod and pitted morningglory control in soybean. Cultivation alone controlled each less than 35% season-long. A cultivation made 7 d after POST applications of AC 263,222 more consistently improved sicklepod and pitted morningglory control than a cultivation made 3 d before, immediately after, or 3 d after the POST application. Imazaquin PRE followed by 18 g ai/ha AC 263,222 controlled sicklepod 88% or more and pitted morningglory 83% or more two of three years. A cultivation made immediately after AC 263,222 POST resulted in reduced soybean yields in several instances compared to the same treatment without cultivation. A cultivation made 7 d after application of AC 263,222 increased soybean yields the most in several instances compared to all other timings.

Field experiments were established to observe the effects of adjuvants and time of application on weed control and ‘Terra-Vig 515’ soybean tolerance with POST applications of AC 263,222. A nonionic surfactant or a crop oil concentrate increased sicklepod control with AC 263,222 applied at either V2 or V6 soybean growth stages. Sicklepod control increased as AC 263,222 was increased from 35 to 70 g ai ha–1 only when applied without an adjuvant. Late in the season, there was no difference in sicklepod control between V2 and V6 applications. Adjuvants and application timing within herbicide treatments had no effect on pitted morningglory control, and, though adjuvants increased common cocklebur control, all treatments controlled more than 85% of both species. AC 263,222 with adjuvants at all rates and timings injured and stunted soybean more 2 wk after treatment compared to AC 263,222 alone. AC 263,222 at 35 or 70 g ha–1 with crop oil concentrate reduced yields more than AC 263,222, with either a surfactant or no adjuvant when applied to V2 soybeans.

Cloransulam postemergence (POST), diclosulam preemergence (PRE), and flumetsulam preplant incorporated (PPI) and POST were evaluated in six trials at two locations for control of sicklepod and pitted morningglory in soybean. Sicklepod control with cloransulam plus flumetsulam POST was equivalent to chlorimuron POST in seven of eight comparisons both 3 and 6 wk after treatment. Sicklepod control with cloransulam POST was equivalent to chlorimuron in only three of eight comparisons 3 wk after treatment, but late-season control was equivalent in five of six comparisons. Pitted morningglory control with cloransulam alone or in tank-mixture with flumetsulam POST was equivalent to chlorimuron in all comparisons. Control of sicklepod and pitted morningglory was greater in most comparisons when a POST application followed flumetsulam plus trifluralin PPI compared to only trifluralin PPI. In a total PRE stale seedbed system, where all treatments were tank-mixed with pendimethalin plus glyphosate, sicklepod control with all rates of flumetsulam and 26 or 35 g ai/ha diclosulam was equivalent to the standard treatment of imazaquin or metribuzin plus chlorimuron. None of the total PRE programs controlled sicklepod as well as when glyphosate was applied sequentially POST. Pitted morningglory was controlled 83 to 93% with 26 or 35 g/ha diclosulam, equivalent to imazaquin, metribuzin plus chlorimuron, or sequential glyphosate applications 8 wk after the PRE application. Increasing flumetsulam rate increased pitted morningglory control early season, but flumetsulam was not as effective as the other herbicides.

The effects of 1.24 kg ha-1 ammonium sulfate, 5 g ae ha-1 of the isopropylamine salt of imazapyr, and air temperature of 18, 27, and 35 C at 40 and 100% relative humidity on the phytotoxicity of 35 g ae ha-1 of the ammonium salt of imazethapyr applied postemergence to pitted morningglory were evaluated. Both ammonium sulfate and imazapyr increased imazethapyr phytotoxicity to pitted morningglory. Ammonium sulfate enhanced imazethapyr phytotoxicity the most at 40% whereas imazapyr was most effective at 100% relative humidity. Imazethapyr phytotoxicity was enhanced more by the combination of ammonium sulfate and imazapyr than with either alone regardless of relative humidity. Variations in temperature had little effect on phytotoxicity.

Field studies were conducted at five locations in North Carolina and Virginia during 1996 and 1997 to evaluate weed control, peanut (Arachis hypogaea) response, and peanut yield following diclosulam applied preplant incorporated (PPI) and in systems with commercial herbicide standards. All plots received a PPI treatment of ethalfluralin at 840 g ai/ha. Ethalfluralin plus diclosulam controlled entireleaf morningglory (Ipomoea hederacea var. integriuscula), ivyleaf morningglory (I. hederacea), pitted morningglory (I. lacunosa), common lambsquarters (Chenopodium album), eclipta (Eclipta prostrata), and prickly sida (Sida spinosa) as well as and frequently better than ethalfluralin PPI followed by (fb) acifluorfen plus bentazon postemergence (POST), paraquat plus bentazon early postemergence (EPOST) fb imazapic POST, or imazapic POST. Systems with ethalfluralin plus diclosulam PPI at 26 g ai/ha fb acifluorfen plus bentazon POST controlled a broader spectrum of weeds and yielded greater than systems of ethalfluralin PPI fb imazapic POST or ethalfluralin PPI fb acifluorfen plus bentazon POST. Peanut exhibited excellent tolerance to diclosulam PPI at 17, 26, or 35 g/ha.

Field experiments were established in 1989 and 1990 on silty clay and sandy loam soils to evaluate selective herbicides in combination with non-selective weed control measures in conventional and stale seedbed soybean production. Metribuzin PRE followed by chlorimuron POST controlled sicklepod better with paraquat than with glyphosate. A POST application of imazaquin increased sicklepod and pitted morningglory control by imazaquin PRE alone in a stale seedbed or tillage program. Pitted morningglory control with imazaquin PRE was lower with tillage than with glyphosate or paraquat combinations in a stale seedbed program. All metribuzin plus chlorimuron PRE treatments, whether conventional tillage or stale seedbed, controlled pitted morningglory more than 75%. Hemp sesbania control was above 80% with all metribuzin followed by chlorimuron or metribuzin plus chlorimuron PRE combinations, and less than 70% with all treatments containing imazaquin. Selective herbicides increased yield in stale seedbed when glyphosate or paraquat was added. Imazaquin PRE, imazaquin PRE followed by imazaquin POST, and metribuzin PRE followed by chlorimuron POST tank mixed with glyphosate or paraquat in a stale seedbed program increased yield compared with the same treatments used with tillage.

Field experiments were conducted in 1989 and 1990 on silty clay and sandy loam soils to evaluate weed control and soybean yield with early-April preplant incorporation of selective herbicides in stale seedbed soybean followed by non-selective weed control measures at planting. Metribuzin applied PPI early followed by chlorimuron POST coupled with either glyphosate or paraquat PRE controlled sicklepod, pitted morningglory, and hemp sesbania to the same extent of that treatment applied PPI at planting. All stale seedbed treatments with POST applications and glyphosate, paraquat, or tillage at planting controlled pitted morningglory over 70%. However, imazaquin or metribuzin applied PPI early without a POST treatment controlled sicklepod and pitted morningglory poorly. Frequently, applying PPI herbicides at planting increased control compared with early PPI applications, but this was overcome by POST treatments. Early stale seedbed applications of metribuzin did not result in more than 60% control of hemp sesbania, whereas metribuzin applied PPI at planting controlled over 85%. However, metribuzin plus chlorimuron controlled hemp sesbania at least 74%, regardless of application timing or tillage method, whereas no imazaquin treatment achieved over 65% control. All stale seedbed herbicide treatments increased soybean yield compared with the untreated stale seedbed check. Selective herbicide treatments with either non-selective herbicide in a stale seedbed program resulted in equivalent yield to PPI at planting treatments most often, except with metribuzin.

Field experiment were conducted to determine interactions of chlorimuron or imazaquin with fomesafen, lactofen, or acifluorfen on three-leaf and eight-leaf common cocklebur, hemp sesbania, pitted morningglory, and prickly sida. Antagonism was the most common interaction with common cocklebur, and was most severe with chlorimuron combined with fomesafen or acifluorfen, whereas lactofen did not antagonize common cocklebur control. Reductions in control were greater when low rates of chlorimuron were used. On three-leaf prickly sida, control synergistically increased when imazaquin was combined with fomesafen or acifluorfen, but the majority of these combinations were additive on eight-leaf prickly sida. Three-leaf pitted morningglory control synergistically increased when 36 g ai ha–1 imazaquin was combined with 210 g ai ha–1 fomesafen or 110 or 220 g ai ha–1 lactofen. With eight-leaf pitted morningglory, synergism occurred when 2 g ai ha–1 chlorimuron was combined with the high rate of any diphenylether herbicide tested, and when 36 g ha–1 imazaquin was combined with 110 g ha–1 lactofen or 210 g ai ha–1 acifluorfen; however, at higher rates of chlorimuron or imazaquin, several antagonistic interactions occurred. Hemp sesbania was controlled over 90% by all combinations, and no interactions occurred.

Field experiments were conducted in 1988 and 1989 to evaluate timing of POST herbicide application in peanut for annual broadleaf weed control, peanut yield, and net returns. Bentazon tank-mixtures with either acifluorfen or paraquat controlled common lambsquarters, prickly sida, and morningglory species equally when applied either at ground-cracking (GC) or 2 wk after ground-cracking (2WGC). Paraquat controlled common lambsquarters least (32 to 33%). Bentazon plus acifluorfen plus BCH 81508S controlled 82% common lambsquarters at 2WGC compared with 66% control from bentazon plus acifluorfen plus a crop oil concentrate. Lactofen controlled 86% common lambsquarters when applied at GC compared to 34% at 2WGC. All applications applied at 4 wk after GC (4WGC) controlled essentially no annual broadleaf weeds. Higher yields and net returns were generally obtained with earlier herbicide applications. Bentazon tank-mixtures with acifluorfen provided equivalent peanut yields and net returns for GC and 2WGC applications.

Field studies were conducted from 1985 to 1987 to evaluate postemergence herbicide systems with preemergence systems to control Texas panicum, Florida beggarweed, sicklepod, and pitted morningglory in peanuts. Adding paraquat at 0.14 kg ai/ha to postemergence herbicide systems reduced fresh weight of Florida beggarweed 92% (18% increase over the same systems without paraquat), sicklepod 95% (21% increase), and pitted morningglory 95% (11% increase). Herbicide systems containing paraquat improved peanut yields by 230 kg/ha and net returns by $52/ha over herbicide systems not containing paraquat. Fluazifop-P and sethoxydim systems reduced Texas panicum fresh weight (at least 96%) more than a preemergence system (92% reduction) that used benefin applied preplant incorporated and alachlor plus naptalam and dinoseb applied at cracking (GC) or a postemergence system that used alachlor and naptalam plus dinoseb GC and paraquat applied early postemergence (86% reduction). Systems containing fluazifop-P provided greater yields (4190 kg/ha) and net returns ($383/ha) than systems containing sethoxydim (4010 kg/ha, $305/ha) when averaged across all rates of application.

Field experiments were conducted from 1985 to 1987 to evaluate herbicide systems for minimum-tillage and conventional-tillage peanut production. While acceptable weed control could be achieved in both tillage systems, minimum-tillage systems generally had to be more herbicide intensive. Preemergence or preplant-incorporated within-the-row applications of either ethalfluralin or pendimethalin plus postemergence applications of paraquat and sethoxydim provided Texas panicum control equivalent to preplant-incorporated applications of ethalfluralin or pendimethalin. Early-postemergence paraquat applications improved Florida beggarweed and pitted morningglory control in conventional-tillage systems at least 15% compared to the same systems without paraquat Control of bristly starbur and sicklepod in conventional-tillage systems did not increase with paraquat application. Broadleaf weed control did not differ between tillage systems, except pitted morningglory control was lower in the minimum-tillage system. Conventional-tillage peanuts produced yields 800 to 1900 kg/ha higher, depending on herbicide system, and also provided greater net returns than minimum-tillage peanuts. The greater yield and net returns in conventional- versus minimum-tillage systems were not attributed to weed control or disease problems.

Data from field studies at Fayetteville, AR, were used to predict the herbicide rate needed to provide 70, 80, or 90% control of a weed based upon weed age. Reduced herbicide rates generally needed to be applied within 6 to 12 d after emergence to control weeds 90%. Reduced rates (280 g ai ha–1 or less) of acifluorfen controlled hemp sesbania, smooth pigweed, Palmer amaranth, and pitted and entireleaf morningglory 90%. Bentazon at 350 to 650 g ai ha–1 controlled common cocklebur and prickly sida 90%. Common cocklebur, smooth pigweed, and pitted morningglory were controlled 90% with chlorimuron at 2 to 5 g ai ha–1 and imazaquin at 20 to 80 g ai ha–1. Prickly sida and hemp sesbania were controlled 90% with imazaquin at 70 g ha–1 and chlorimuron at 6 g ha–1, respectively. Barnyardgrass, large crabgrass, red rice, and sicklepod were not controlled with reduced herbicide rates.