Experiments were conducted at three locations in Louisiana from 1992 to 1994 to evaluate broadleaf weed control with sulfentrazone. Sulfentrazone at 0.42 kg ai/ha applied PPI or PRE provided at least 93% control of entireleaf morningglory in all years at all locations, which was greater than control with metribuzin PRE. Prickly sida control with sulfentrazone ranged from 83 to 94%, which was equal to or greater than control with metribuzin. Hemp sesbania and sicklepod control with sulfentrazone was unacceptable (≤75%) regardless of application method and generally was lower than control with metribuzin. Greater than 90% control of smellmelon and hophornbeam copperleaf was observed with all treatments. Minor but transient soybean injury was noted at one location in one year. Soybean yields following sulfentrazone PRE at St. Joseph were greater than yields with metribuzin as a result of the general increase in broadleaf weed control.

Greenhouse studies were conducted to investigate the effects of adjuvant and rainfall on bentazon spray retention, efficacy, and foliar washoff in hemp sesbania, sicklepod, smooth pigweed, and velvetleaf. Bentazon was applied at 0.28 to 2.24 kg ai/ha with Agri-Dex, a crop oil concentrate (COC) or Kinetic, an organiosilicone-nonionic surfactant blend (OSB) when weeds were at the three- to five-leaf stage. Plants were subjected to 2.5 cm simulated rainfall for 20 min at 1 and 24 h after application of bentazon. Shoot fresh weight reduction assessed 2 wk after treatment was similar with either adjuvant on velvetleaf and smooth pigweed. OSB enhanced bentazon efficacy in hemp sesbania and sicklepod as compared to COC. Rainfall at 1 h after application generally reduced bentazon activity in all weeds. OSB maintained bentazon activity in hemp sesbania when subjected to rainfall at 1 h after application as compared to COC. Overall, bentazon spray retention on plants was 9 to 550% higher with OSB as compared to COC among the species at 1 h after application. Amount of bentazon residue washed off from the foliage by rainfall within a weed species was relatively similar for both adjuvants except in smooth pigweed and ranged from 39 to 98% among the four weed species at 1 h after application. OSB exhibited specificity for certain weed species and the potential to minimize bentazon spray reaching the soil by increasing deposition.

Field experiments were conducted from 1993 to 1995 to compare weed control by the isopropylamine salt of glyphosate at 0.21, 0.42, 0.63, and 0.84 kg ae/ha applied at three stages of weed growth. Weed control by glyphosate applied at these rates alone or with ammonium sulfate at 2.8 kg/ha was also evaluated. In other experiments, potential interactions between glyphosate and acifluorfen, chlorimuron, and 2,4-DB were evaluated. Velvetleaf, prickly sida, sicklepod, pitted morningglory, entireleaf morningglory, palmleaf morningglory, and hemp sesbania were controlled more easily when weeds had one to three leaves compared with control when weeds had four or more leaves. Glyphosate controlled redroot pigweed, velvetleaf, prickly sida, sicklepod, and barnyardgrass more effectively than pitted morningglory, entireleaf morningglory, palmleaf morningglory, or hemp sesbania. Increasing the rate of glyphosate increased control, especially when glyphosate was applied to larger weeds. Greater variation in control was noted for pitted morningglory, palmleaf morningglory, prickly sida, and velvetleaf than for redroot pigweed, sicklepod, entireleaf morningglory, or hemp sesbania. Ammonium sulfate increased prickly sida and entireleaf morningglory control but did not influence sicklepod, hemp sesbania, or barnyardgrass control. Acifluorfen applied 3 d before glyphosate or in a mixture with glyphosate reduced barnyardgrass control compared with glyphosate applied alone. Chlorimuron did not reduce efficacy. Mixtures of glyphosate and 2,4-DB controlled sicklepod, entireleaf morningglory, and barnyardgrass similar to glyphosate alone.

A tandem mass spectrometric procedure was developed to detect sesbanimide A and its isomers in plant materials. Analysis of seed extracts from 10 Sesbania species using this procedure readily detected sesbanimides in Drummond rattlebush, rattlebush, and bagpod sesbania. The toxic sesbanimides were not detected in hemp sesbania or in other species with no known history of animal toxicity.

Sicklepod (Cassia obtusifolia L. ♯6 CASOB), hemp sesbania [Sesbania exaltata (Raf.) Cory ♯ SEBEX], and showy crotalaria (Crotalaria spectabilis Roth. ♯ CVTSP) were grown in controlled-environment greenhouses with day/night temperatures of 23/17, 26/20, 29/23, and 32/26 C. Plant height, leaf area, and total dry weight at 53 days after planting increased significantly with temperatures between 23/17 and 29/23 C in sicklepod and showy crotalaria, and between 23/17 and 32/26 C in hemp sesbania. In all species, leaves were produced more rapidly as temperature increased. Axillary branch leaf production was greatest at 29/23 C in sicklepod, and at 29/23 and 26/20 C in showy crotalaria; hemp sesbania showed little axillary branch development. Total dry-matter production in all species was closely correlated with leaf area duration, but not with net assimilation rate. Differences in total main stem leaf area in all species were primarily due to differences in leaf number rather than to differences in leaf size at maturity.

Field studies were conducted from 1988 to 1990 on a Sharkey clay to evaluate residual weed control in rice with quinclorac applied PPI, PRE to dry soil, and PRE to moist soil. Quinclorac applied at 0.4 or 0.6 kg ai ha−1 PPI or PRE to dry or moist soil controlled more than 80% of barnyardgrass, pitted morningglory, and hemp sesbania without rice injury. Quinclorac applied at 0.3 kg ha−1 controlled these three weed species substantially but inconsistently. No rice injury was observed from any quinclorac treatment. Except for one of three years when irrigation was delayed for 7 d after PRE application to dry soil, application timing did not consistently affect weed control or rice yield.

In 12 trials in Louisiana, sicklepod, entireleaf morningglory, pitted morningglory, and hemp sesbania control 4 wk after planting was greater with trifluralin applied PPI followed by chlorimuron plus metribuzin applied PRE than with trifluralin plus flumetsulam applied PPI. Sicklepod control with these herbicides was similar 6 wk after application. No differences in soybean yield were noted. Chlorimuron applied POST following trifluralin applied PPI and metribuzin applied PRE or trifluralin plus flumetsulam applied PPI improved weed control and soybean yield compared with soil-applied herbicides alone. Excellent barnyardgrass control was obtained with all herbicide programs.

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.

Soil-applied herbicides alone or followed by postemergence (POST) applications of CGA-277476 were evaluated for season-long weed control in soybean. Common cocklebur, hemp sesbania, and pitted morningglory control was not consistently improved with a soil-applied herbicide followed by a POST application of 79 g ai/ha CGA-277476. However, in locations with heavy weed pressure, a tank-mix of chlorimuron + metribuzin + trifluralin or imazaquin + pendimethalin followed by CGA-277476 improved common cocklebur, hemp sesbania, and pitted morningglory over CGA-277476 alone. Sequential application of CGA-277476 following SAN 582 improved weed control over SAN 582 alone. When weed pressure was not severe, there were no differences in control from CGA-277476 alone or following soil-applied herbicides. A POST application of CGA-277476 following soil-applied herbicides did not consistently improve soybean yield over CGA-277476 alone. Yield from soybean treated with SAN 582 was improved when CGA-277476 was applied. In contrast, when chlorimuron + metribuzin + trifluralin or imazaquin + pendimethalin were applied at planting, yield was similar with or without POST application of CGA-277476.

Broadleaf weed control with DPX-PE350 at 56, 84, 110, 140, and 170 g ae ha−1 applied postemergence was evaluated. DPX-PE350 was less effective and higher rates were required when applied to three- to six-leaf weeds compared to one- to two-leaf weeds. Listed in order of increasing susceptibility are sicklepod, tall morningglory, pitted morningglory = palmleaf morningglory, and entireleaf morningglory = hemp sesbania = velvetleaf.

Multiherbicide granules were formulated containing 1.3% fluazifop {(±)-butyl 2-[4-[[5-trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoate} (w/w) in polymerized tung oil overlaid on a granular matrix of gum xanthan-loess containing 2.7% linuron [3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea] or oryzalin (3,5-dinitro-N4,N4-dipropylsulfanilamide). Under greenhouse conditions the granules were as effective in selective control of velvetleaf (Abutilon theophrasti Medic. ♯3 ABUTH), hemp sesbania [Sesbania exaltata (Raf.) Cory ♯ SEBEX], corn (Zea mays L. ♯ ZEAMX), and red rice (Oryza sativa L. ♯ ORYSA) in soybeans [Glycine max (L.) Merr. ‘Hill’] as when the herbicides were sprayed separately. When applied preemergence at 0.56 to 0.14 kg ai/ha, tung oil-encapsulated fluazifop on loess granules killed 100% of stolon bermudagrass [Cynodon dactylon (L.) Pers. ♯ CYNDA] and was as effective as sprayed fluazifop.

When formulated and sprayed in an invert emulsion (IE), conidia of the mycoherbicide, Colletotrichum truncatum, controlled hemp sesbania in the absence of dew. To optimize hemp sesbania control, formulation droplet size influence upon the pathogen's germination and pathogenicity was investigated. Conidia germination in manually produced IE droplets decreased from 46% to 5% as droplet diameter decreased from 2700 to 900 μm. Droplet size did not affect appressoria formation. On a per conidium basis, 900-μm droplets were more pathogenic to detached hemp sesbania leaves than were 2100-μm droplets. An air-assist spray system produced droplet spectra with volume median diameters of 421 and 104 μm, respectively. The spectrum of smaller droplets covered the target better than did that of larger droplets. When applied to whole hemp sesbania plants in greenhouse trials, conidia in the smaller and larger droplet spectra gave 90 and 94% control, respectively. Sufficient conidia germinated in IE droplets of a variety of sizes to control hemp sesbania excellently.

Mefluidide {N-[2,4-dimethyl-5-[[(trifluoromethyl)sulfonyl]-amino] phenyl] acetamide} was applied postemergence in soybean [Glycine max (L.) Merr.] fields and its effectiveness in controlling johnsongrass [Sorghum halepense (L.) Pers.], hemp sesbania [Sesbania exaltata (Raf.) Cory], and common cocklebur (Xanthium pensylvanicum Wallr.) was evaluated. In plots treated preplanting with trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine), mefluidide gave 95% johnsongrass control when it was applied postemergence (over-the-top without surfactant) once at 0.90 kg/ha or twice at 0.44 kg/ha. Directed sprays of mefluidide at 0.22 to 0.67 kg/ha without surfactant were more effective on johnsongrass than similar treatments applied over-the-top. When 0.5% (v/v) nonoxynol [α-(p-nonyl-phenyl)-ω-hydroxypoly (oxyethylene)] surfactant was added, mefluidide at 0.44 or 0.67 kg/ha applied as directed or over-the-top sprays provided 76 to 90% johnsongrass control. Mefluidide at 1.12 kg/ha plus nonoxynol surfactant, applied as a directed spray, was required to provide 81% control of hemp sesbania. Directed sprays containing mixtures of mefluidide at 0.28 kg/ha plus dinoseb (2-sec-butyl-4,6-dinitrophenol) at 2.2 kg/ha, or mefluidide at 0.28 kg/ha plus a 2:1 mixture of naptalam (N-1-naphthylphthalamic acid)/dinoseb at 4.7 L/ha, effectively controlled 40- to 60-cm-tall hemp sesbania. A single, directed spray of mefluidide at 0.56 kg/ha plus nonoxynol provided 92% common cocklebur control, and mixtures of mefluidide at 0.28 kg/ha plus dinoseb at 2.2 kg/ha or naptalam/dinoseb (a 2:1 mixture) at 4.7 L/ha increased control above that provided by either of the herbicides alone.

In field tests, common cocklebur (Xanthium pensylvanicum Wallr.) was controlled at the one- and two-leaf stages with 0.3 kg/ha acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid}. Four-leaf common cocklebur required 1.1 kg/ha for comparable control. Acifluorfen at 0.6 and 0.8 kg/ha controlled 96 and 90% of entireleaf morningglory [Ipomoea hederacea (L.) Jacq. var. integriuscula] atone- and two-leaf stages, respectively, but control was reduced as plants aged. Dark applications (2100 h) were more effective than those at sun-up (0600 h) or midday (1200 h) in control of hemp sesbania [Sesbania exaltata (Raf.) Cory], pitted morningglory (Ipomoea lacunosa L.), and smooth pigweed (Amaranthus hybridus L.). Hour of application had no significant influence on control of common cocklebur or prickly sida (Sida spinosa L.). An increase in surfactant (80% alkyl aryl polyoxyethylene glycols) concentration enhanced acifluorfen control of entireleaf morningglory and Texas gourd [Cucurbita texana (A.) Gray] at the 0.3-kg/ha rate applied 2 weeks after emergence. Soybean [Glycine max (L.) Merr.] injury was increased with the 1.1-kg/ha rate when surfactant concentration was increased from 0.5 to 0.75%. Increasing the spray volume increased pitted morningglory control but decreased hemp sesbania control. In the growth chamber, better control of pitted morningglory and common cocklebur was obtained at high (35 C day, 26 C night) than at low temperatures (27 C day, 18 C night) when plants were treated 1 week after emergence.

The initial metabolism of acetochlor [2-chloro-N-(ethoxymethyl)-N-(2-ethyl-6-methylphenyl)acetamide] in tolerant and susceptible plants was examined to determine if metabolism is a factor in the selective phytotoxicity of this herbicide. Six crop and ten weed species were used. In every case acetochlor was converted initially to thioether conjugates. In thirteen of the species, initial conjugation was with glutathione (GSH). The homoglutathione (hGSH) conjugate was formed in three legumes. Tolerant plant seedlings metabolized acetochlor more readily than susceptible plant seedlings. Based on these results, acetochlor detoxification is a primary factor in the selective phytotoxicity of this herbicide.

Disk harrowing, spring tooth harrowing, and bed conditioning, alone or followed by bedding the rows, were evaluated in field studies to determine their efficacy to soil incorporate trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) plus metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazine-5 (4H)-one] in soybeans [Glycine max (L.) Merr.]. Effects of the time interval between herbicide application and soybean planting were also evaluated. Effective weed control and adequate crop selectivity were obtained from all incorporation methods except those followed by bedding. Bedding occasionally reduced weed control and soybean stands as compared to incorporation without bedding. Excessive crop injury resulted from the application of a band of the herbicide mixture as a subsurface layer. The herbicide mixture was applied up to 6 weeks before soybean planting without adversely affecting crop or weed selectivity when incorporated with the spring tooth harrow without bedding.

Barnyardgrass and morningglory control POST with glufosinate at 840 g a.i./ha 28 d after treatment was 79 to 85% and 83 to 90%, respectively, when no more than 35 d elapsed between initial spring soil tillage and herbicide application. For the same rate of glufosinate, prickly sida and hemp sesbania were controlled 68 and 92%, respectively. Comparable barnyardgrass control was obtained with glufosinate at 560 and 840 g/ha, which was greater than at 420 g/ha. Hemp sesbania control was similar for all rates of glufosinate. In comparison, paraquat at 1050 g a.i./ha controlled 40 to 65% barnyardgrass, 44 to 75% morningglory, 41% prickly sida, and 92% hemp sesbania. With 840 g a.i./ha glyphosate and SC-0224, barnyardgrass, morningglory, prickly sida, and hemp sesbania were controlled 55 to 89%, 55 to 81%, 45 to 61%, and 56 to 68%, respectively. Soybean yield was 5.8, 7.6, 6.0, and 5.9 times greater than the nontreated check for 1050 g/ha paraquat and 840 g/ha glufosinate, glyphosate, and SC-0224, respectively.

The commercial development of microbial bioherbicides requires the availability of low-cost production methods. The use of liquid culture fermentation is generally considered necessary to achieve this goal. Our strategy for optimizing liquid culture media is based on using defined nutritional conditions. Specific changes are made in the nutritional environment of the medium and the effect of these changes is assessed in terms of propagule yield, efficacy, and stability of the bioherbicidal agent. Liquid culture studies with the fungus Colletotrichum truncatum have demonstrated that nutrition impacts not only spore yield but also spore efficacy in controlling the weed hemp sesbania. Nutritional conditions were identified which suppressed sporulation and promoted the production of high concentrations of C. truncatum microsclerotia in liquid culture. Microsclerotia of C. truncatum (particle size range = 180 μm to 425 μm) showed promise as bioherbicidal propagules due to their stability as a dry preparation and their efficacy in controlling hemp sesbania when used as a soil amendment. By understanding how nutrition impacts propagule formation, yield, efficacy, and stability, rational approaches can be taken to develop submerged culture production methods for microbial biocontrol agents. Breakthroughs in these areas should allow numerous promising bioherbicidal agents to become commercial products.

Glyphosate-resistant (Roundup Ready®) soybean is widely grown to provide broad-spectrum weed control following sequential applications of glyphosate. Studies were conducted during 1998 and 1999 at Keiser, AR, and in 1999 at Pine Tree, AR, to examine the effect of glyphosate-resistant soybean populations on the number of glyphosate applications needed to maintain 90% or greater control of all weed species and on the gross profit margin from weed management. Soybean was seeded in 19-cm rows at 12 rates ranging from 185,000 to 1,482,000 seeds/ha. Each seeding rate received a single application of 0.56 and 1.12 kg ai/ha glyphosate once weeds were 5 to 7 cm tall, followed by repeat applications when control of any species fell below 90%. Soybean yield and gross profit margin at Keiser were similar both years, and a quadratic curve best described the relationship between seed yield and seeding rate, with maximum predicted and observed yield at 988,000 seeds/ha. Soybean seeding rate affected light interception by soybean and the number of glyphosate applications needed to maintain 90% control of all species. By the later stages of vegetative development, soybean at Pine Tree achieved ≥95% light interception, maximizing yield at all seeding rates. Late-season light interception at Keiser ranged from 88 to 99%, causing soybean yield to vary by seeding rate. Three applications of 0.56 kg/ha glyphosate were needed at seeding rates of 185,000 and 247,000 seeds/ha, whereas higher seeding rates sometimes required only a single application for season-long weed control. Application and herbicide costs were offset by reduced seeding costs; thus, predicted gross profit margin from weed management was optimized at the lowest seeding rate of 185,000 seeds/ha.