The degradation of 14C-labeled metolachlor, acetochlor, and pretilachlor in control and soils with 10-yr metolachlor- history or 3-yr butylate history was studied by monitoring the evolution of 14CO2 in soil biometer flasks. The degradation rate of 14C-phenyl-labeled metolachlor was similar in soils with 0- and 10-yr metolachlor history over 52 d. 14C was released from carbonyl-labeled metolachlor about 40% faster than from phenyl-labeled metolachlor in both soils. Soil sterilization by autoclaving reduced significantly the metolachlor degradation rate in both soils. Degradation of 14C-labeled EPTC in soils with 3-yr butylate history was much faster than in soils with no history. Soil sterilization reduced the EPTC degradation rate, confirming microbial degradation. The degradation rates of acetochlor, metolachlor, and pretilachlor were similar in soils with and without butylate history. Most of the 14C that remained in history and nonhistory soils was extractable with ethyl acetate or sodium hydroxide. Three major metabolites of metolachlor and EPTC were detected by thin-layer chromatography (TLC) of extracts from both soils. In contrast to the situation with carbamothioate herbicides, soils exposed repeatedly to metolachlor or other acetanilides are not prone to become adapted to these herbicides. Soils with carbamothioate history did not exhibit any apparent cross-adaptation toward acetanilide herbicides.

Field experiments were conducted near Marianna, Trenton, and Archer, FL in 1990 and 1991 to investigate the effect of nicosulfuron mixtures and time of application on five peanut cultivars. Nicosulfuron at 54 g ai/ha was applied alone or in mixture with 2,4-DB at 280 g ai/ha 5 weeks after planting (WAP), 9 WAP, or 5 plus 9 WAP. Injury was greater from early and sequential nicosulfuron applications while a single application 9 WAP typically did not cause significant injury or reduce peanut yield. The 5 WAP and 5 plus 9 WAP applications often caused early visible injury and sometimes reduced peanut yield. When peanut yields were compared, ‘Florigiant’ was the most sensitive cultivar while ‘Southern Runner’ and ‘Valencia’ were more tolerant to nicosulfuron. ‘Sunrunner’ and ‘NC-7’ were intermediate in tolerance to nicosulfuron. In several instances, the addition of 2,4-DB to nicosulfuron reduced initial crop injury and ameliorated yield losses resulting from nicosulfuron applied alone.

When spray mixtures were examined using a laser spray droplet analyzer, the new isopropylamine glyphosate formulation produced more small droplets than a previous isopropylamine salt of glyphosate formulation or glyphosate–trimesium plus nonionic surfactant. The use of a pre-orifice flat-fan nozzle and an impact type flat-fan nozzle reduced the amount of small droplets produced compared to an existing extended range flat-fan nozzle, while maintaining a spray droplet distribution that could still provide good weed control. The new nozzle technologies could provide a useful management tool to manage potential drift situations.

Field trials were conducted in no-till field corn in northern Missouri to compare weed control and crop response of metolachlor plus atrazine applied under five preplant herbicide management practices. The practices consisted of (1) applying the entire dose of metolachlor plus atrazine 15, 30, or 45 d early preplant (EPP), (2) applying a split application of an EPP (67%) followed by (fb) a PRE (33%), (3) applying the entire dose PRE, (4) applying metolachlor PRE fb dicamba early post (EPOST), or (5) applying atrazine alone EPOST. Weed control at 7 wk after planting was more variable with EPP treatments than with EPP fb PRE or PRE treatments. Giant foxtail and fall panicum control was greatest with treatments that included metolachlor PRE. Velvetleaf and common cocklebur control was greatest with atrazine or dicamba EPOST and was generally unacceptable (< 80%) with any soil-applied herbicide treatment. Common lambsquarters control was greater than 90% with all treatments that included metolachlor, atrazine, or dicamba, regardless of timing. Corn yields were slightly higher with EPP fb PRE and PRE fb EPOST dicamba than with EPP alone. The results suggest that herbicide applications made nearer to the date of planting provide less variable weed control and corn yield than treatments made more than 15 d EPP.

Control of downy brome in cool-season perennial grasses grown for seed production must be done prior to seed harvest, because downy brome seeds cannot be separated from cool-season grass seeds. Field experiments were conducted near Powell, WY, and Bridger, MT, to evaluate several herbicides for control of downy brome from 1992 through 1994 in western wheatgrass, slender wheatgrass, beardless wild rye, thickspike wheatgrass, and meadow bromegrass. When fall-applied, only metribuzin at 0.4 kg/ha and oxyfluorfen plus metribuzin at 1.1 plus 0.3 kg/ha controlled 98 and 95% of the downy brome, respectively, without affecting grass seed viability or seed yield. Early spring applications of paraquat at 0.8 kg/ha controlled 100% of the downy brome, but suppressed perennial grasses. Glyphosate applied in early spring at 0.3 kg/ha controlled 48% of the downy brome, but suppressed perennial grasses. Seed yield reductions occurred when thickspike wheatgrass and meadow brome were treated with glyphosate at 0.3 kg/ha.

A three-year field study in west-central Kansas investigated the effects of combinations of spray carrier, nonionic surfactant (NIS), triasulfuron, and/or 2,4-D on winter wheat foliar injury and grain yield. Herbicides applied in water without NIS caused little or no foliar injury in two of three years. Urea-ammonium nitrate (UAN) at 112 L/ha (40 kg N/ha) alone or as a carrier for herbicides caused moderate to severe foliar injury in all three years. Adding NIS to UAN spray solutions increased foliar injury, especially with the tank mixture of triasulfuron + 2,4-D. Effects of triasulfuron + NIS or 2,4-D applied in UAN were additive. Foliar injury was related inversely to temperature following application. Foliar injury was most evident 4 to 7 d after application and disappeared within 2 to 3 wk. Diluting UAN 50% with water lessened foliar injury in two of three years, especially in the presence of NIS, regardless of whether herbicides were in the spray solution. Treatments did not reduce wheat grain yield in any year despite estimates of up to 53% foliar injury one year.

Eight polymers capable of forming aqueous gels were compared for their capacity to retain hydration over time, to promote spore germination, and to prolong the viability of germinated spores (= germlings) of Alternaria cassiae, a bioherbicide agent for sicklepod. When compared at a standard 0.1% w/w (gel/water) concentration, the eight gels retained hydration for 6 d with no significant differences among them in the rate of dehydration. The best concentration of each gel that yielded 95 to 100% spore germination within 6 h after hydration was then chosen, and the gels were compared at these concentrations to determine the duration of effectiveness of the gels. The effectiveness was rated on the basis of the proportions of alive germlings versus germinated spores and alive germlings versus total spores, determined with the aid of a fluorescent vital stain. Based on these two parameters, the most effective gel was Kelzan® xanthan gum. However, all gels supported > 50% alive germlings over a period of 1 wk, suggesting that the addition of any of these polymers to the inoculum suspension should enable the fungal propagules to remain moist for a prolonged period, benefit from the high ambient moisture to improve germination, and promote disease development. Accordingly, seven of these gels were tested for their ability to enhance pathogenicity of a mycelial inoculum of A. eichhorniae, a bioherbicide agent for waterhyacinth. Gellan gum and Kelgin®-HV were most effective in promoting disease, followed by Evergreen® 500 polyacrylamide, and Kelgin®-LV, Metamucil®, Kelzan® xanthan gum, and N-Gel™ were no better than the control inoculum without any gel. Thus, the gels may have differential effects on different fungi and inoculum types. Nonetheless, the results confirm the utility and feasibility of hydrophilic gels as formulating materials for bioherbicides.

Soil- and foliar-applied herbicide treatments were evaluated for the control of seedling johnsongrass in the interim between row formation and the planting of fallowed sugarcane fields approximately 90 d later. Soil-surface applications of metribuzin at 1,680 g ai/ha, pendimethalin plus atrazine each at 2,240 g ai/ha, terbacil at 1,680 g ai/ha, and sulfometuron at 35 and 70 g ai/ha and an incorporated application of trifluralin at 2,240 g ai/ha followed by a surface application of atrazine at 2,240 g/ha did not consistently control seedling johnsongrass until the crop was planted. Rhizome johnsongrass populations originating from seedling johnsongrass that escaped the fallow treatments were lowest in the newly planted crop when sulfometuron at 140 to 280 g/ha was applied to the soil surface and when glyphosate was applied POST at 2,240 g ai/ha, particularly as a sequential treatment alone or as a spot treatment at 2% by volume following applications of metribuzin, terbacil, and pendimethalin or trifluralin with atrazine. Sugarcane shoot populations in the fall after planting and sugar yields at the end of the crop's first growing season were highest where fallow treatments minimized johnsongrass development. These treatments also provided broad spectrum control of other seedling weeds, the residues of which influenced crop development.

Research was initiated to determine (a) whether a common waterhemp population was resistant to acetolactate synthase (ALS) inhibiting herbicides, (b) the percentage of the population that was ALS-inhibitor resistant, (c) the resistance mechanism, and (d) the effectiveness of a whole plant assay to detect ALS-inhibitor resistance. ALS-inhibitor resistance was confirmed in a common waterhemp population near Davis City, IA. The Davis City common waterhemp population was cross resistant to both imidazolinone and sulfonylurea herbicides, but not to lactofen. Approximately 10% of the Davis City common waterhemp population was sensitive to a rate of imazaquin 4 times the normal field rate. Davis City common waterhemp isolated ALS was much less sensitive to imazaquin and primisulfuron inhibition than was grain amaranth or an ALS-sensitive common waterhemp isolated ALS. Imazaquin I50 values were 366.4 and 3.4 μM for ALS isolated from Davis City common waterhemp and grain amaranth, respectively. Primisulfuron I50 values were 3.6 and 0.007 μM for ALS isolated from Davis City common waterhemp and grain amaranth, respectively. A whole plant ALS assay was developed that allowed for much more rapid detection of an ALS-resistant species and used less plant material than a conventional ALS assay.

Broadleaf weed and yellow nutsedge control with herbicide programs containing pendimethalin and combinations of fomesafen, fluometuron, and norflurazon applied alone or with POST-directed applications of MSMA or fluometuron plus MSMA was evaluated. Soil-applied herbicide combinations containing fomesafen controlled yellow nutsedge better than combinations of norflurazon and fluometuron but did not provide better entireleaf, ivyleaf, pitted, and tall morningglory or sicklepod control. Fluometuron plus MSMA controlled morningglories and sicklepod more effectively than MSMA. Seed cotton yield was greater in one of two years when fomesafen was applied and was associated with better yellow nutsedge control.

Experiments were conducted in pots and in the field to determine the influence of seed depth on seedling emergence pattern and control of Mexican sunflower with or without imazethapyr plus pendimethalin. Mexican sunflower seeds were placed at 0-, 2.5-, 5-, 7.5-, and 10-cm soil depths, and imazethapyr–pendimethalin mixture was applied PRE at 0, 0.05 + 0.65, 0.09 + 1.31, and 0.18 + 2.62 kg ae (+ ai)/ha. Mexican sunflower emergence was 57, 30, 14, 3, and 2% from 0-, 2.5-, 5-, 7.5-, and 10-cm seed depths, respectively. Seedling emergence started 2 to 3 d after planting and continued for 4 to 5 d. At 0- to 5-cm seed depths, 84 to 100% of total seedling emergence occurred within 3 d after the first seedling emerged, but emergence rate was less from 7.5- and 10-cm seed depths. Imazethapyr plus pendimethalin at 0.05 + 0.65 and 0.09 + 1.31 kg/ha had no effect on seedling emergence in Mexican sunflower, but subsequent growth was severely inhibited regardless of seed depth. The herbicide treatments were more injurious to Mexican sunflower seedlings that emerged from 5- to 10-cm depths than to those that emerged from 0 and 2.5 cm. Burying seeds 7.5 cm deep or more is a potential control measure for Mexican sunflower, and the deeper the emergence depth, the more susceptible the seedling is to imazethapyr plus pendimethalin.

Research was conducted in 1995 and 1996 to determine the potential for commonly used volunteer corn herbicides to control volunteer sethoxydim-resistant (SR) corn in soybean. Greenhouse studies showed that the SR corn hybrid tolerated 181 times more sethoxydim than the susceptible sister hybrid. SR corn also tolerated other acetyl CoA carboxylase (ACCase) inhibitors including fluazifop-P, quizalofop-P, and clethodim with 30 X, 27 X, and 7 × magnitudes of tolerance, respectively, compared with the susceptible hybrid. SR corn exhibited the least tolerance to clethodim, with a control rating of 50% (CR50) predicted at 28 g ai/ha. Field studies at Dekalb and Urbana, IL, showed that quizalofop-P, fluazifop-P, and fluazifop-P plus fenoxaprop at 62, 140, and 140 + 47 g ai/ha, respectively, controlled 22% or less of volunteer F2 SR corn at 30 days after treatment (DAT). Clethodim at 105, 140, and 210 g/ha consistently suppressed 23 to 70% of the volunteer SR corn. Dry weight reductions at 60 DAT showed the same general trend as the visual estimates of control. The field results confirmed the greenhouse data, which suggested SR corn had the least amount of cross-resistance to clethodim compared to other ACCase-inhibiting herbicides. In 1996, only AC 299,263 and imazethapyr plus imazaquin suppressed volunteer SR corn and prevented soybean yield loss at both locations. However, no system completely controlled volunteer SR corn.

Greenhouse and field experiments were conducted to evaluate herbicidal efficacy on tropical soda apple and bahiagrass. Acifluorfen, clopyralid, dicamba, fluroxypyr, picloram, and triclopyr were the most effective postemergence herbicides, providing > 90% control of tropical soda apple plants with no injury to bahiagrass 145 days after treatment (DAT). Glyphosate and imazapyr resulted in effective (> 90%) control of both seedling and mature tropical soda apple plants. However, these herbicides caused severe (> 90%) damage to bahiagrass. Control of tropical soda apple with 2,4-D, AC-263,222, diuron, fomesafen, lactofen, MSMA, sulfometuron, and triasulfuron was unacceptable (> 90%).

In an attempt to refine calibration procedures for greenhouse spray chambers, the effects of an herbicide adjuvant, operating pressure, and travel speed on the static and dynamic spray patterns of single flat-fan hydraulic nozzle tips were studied. The volume output in the central 15 cm of the spray pattern (where target plants would ordinarily be positioned) was used as an indicator of the relative dosages received from both a tapered flat-fan tip (8001 VS) and an even-spray tip (8001 EVS). All tested variables significantly altered the spray pattern. Specifically, dynamic spray patterns differed from static patterns, and speed of travel affected the dynamic pattern for both tapered and even flat-fan sprays. Increasing the travel speed from 0.375 to 0.75 m/s reduced spray deposit in the central 15 cm of the spray pattern by up to 19% for water, and by up to 34% for water containing 0.1% v/v nonionic surfactant. Increasing surfactant concentration to 1% decreased the magnitude of the speed effect. Higher pressure sprays tended to reduce the effect of increased travel speeds. These results show that changes in physicochemical properties of the spray solution as well as air turbulence introduced by nozzle movement can affect the pesticide dosage to which a target plant is exposed in a spray chamber. For proper treatment comparison, delivery systems for greenhouse spray experiments should be calibrated with end-use spray liquids, operating pressures, and nozzle travel speeds.

Systems consisting of flumetsulam, metribuzin plus chlorimuron, or imazaquin applied PPI with trifluralin or PRE with metolachlor were compared with and without chlorimuron POST for control of sicklepod and entireleaf morningglory in narrow-row soybean at four locations. Control of sicklepod and entireleaf morningglory by soil-applied herbicides was generally inadequate. Control of sicklepod by flumetsulam exceeded control by metribuzin plus chlorimuron or imazaquin at one location. Entireleaf morningglory control by flumetsulam was similar to or less than control by metribuzin plus chlorimuron or imazaquin. Chlorimuron POST was a more important component of management systems for these weeds than was flumetsulam, metribuzin plus chlorimuron, or imazaquin PPI or PRE. Pooled over soil-applied herbicides, chlorimuron POST increased late-season control of sicklepod and entireleaf morningglory 25 to 61% and 22 to 54%, respectively; increased soybean yield 20 to 55%; decreased foreign matter contamination 5 to 13%; and increased net returns $34 to $185/ha. When used in conjunction with chlorimuron POST, flumetsulam, metribuzin plus chlorimuron, and imazaquin applied PPI with trifluralin or PRE with metolachlor increased late-season control of sicklepod and entireleaf morningglory only when control by trifluralin or metolachlor followed by chlorimuron POST was less than 66 and 77%, respectively.

Hemp sesbania control by chlorimuron applied with crop oil concentrate at 1.0% v/v, BCH 815 at 1.0% v/v, methylated seed oil at 1.0% v/v, a blend of methylated seed oil and organosilicone surfactant at 0.5% v/v, organosilicone-based surfactant at 0.125% v/v, and nonionic surfactant at 0.25% v/v was evaluated in field studies in 1994 and 1995. Control by chlorimuron at 4.5 g ae/ha was greater when applied with BCH 815, organosilicone-based surfactant, and nonionic surfactant than with crop oil concentrate, methylated seed oil, and a blend of methylated seed oil and organosilicone surfactant. When chlorimuron was applied at 4.5 g/ha with BCH 815 or nonionic surfactant, hemp sesbania control was similar to that by chlorimuron at 9 g/ha applied with methylated seed oil, the blend of methylated seed oil and organosilicone surfactant, or organosilicone-based surfactant.

Redroot pigweed and common lambsquarters control was variable within and between seasons when postemergence linuron and metribuzin were applied one or two times at below-labeled rates to one-, three-, or five-leaf carrots. A single, low-rate application of either herbicide at the one-or three-leaf stage of carrots failed to provide adequate season-long broadleaf weed control. Two low-rate applications to either one- + three- or three- + five-leaf carrots significantly improved control. Linuron produced little or no injury to carrots regardless of application timing. Metribuzininduced injury was variable initially and decreased to 10% or less by 14 d after treatment. One application of either linuron or metribuzin resulted in reduced yields of carrots.

Control and regrowth of hemp dogbane, wild blackberry, and triazine-resistant common lambsquarters (TR-CHEAL) were studied in no-till corn from 1992 to 1994. Hemp dogbane, wild blackberry, and TR-CHEAL population increased 10, 123, and 177%, respectively, between 1992 and 1994 in plots treated with PRE applications of paraquat, atrazine, and metolachlor (weedy checks). POST applications of tank mixtures of 35 g ai/ha nicosulfuron or 20 g/ha primisulfuron with 280 g/ha 2,4-D or 140 g/ha dicamba, and 560 g/ha dicamba applied alone controlled hemp dogbane, wild blackberry, and TR-CHEAL 67 to 98%. These treatments reduced the population or prevented expansion of these weeds the year following treatment. In 1992, corn yield response to weed control was inconsistent. In 1993 and 1994, all plots treated with POST herbicides yielded higher than the weedy check. Corn yield of plots treated with combinations of nicosulfuron or primisulfuron with 2,4-D or dicamba and 560 g/ha dicamba applied alone were 102 to 149% and 124 to 153% higher than the weedy check in 1993 and 1994, respectively.

Overseeding established kikuyugrass swards with tall fescue or perennial ryegrass reduced kikuyugrass cover. Renovation prior to seeding did not aid in the establishment of these two species. Increasing the seeding rate from 79 to 157 kg/ha improved the establishment of perennial ryegrass but not tall fescue. When kikuyugrass plugs were introduced into established turf, tall fescue reduced the invasion of kikuyugrass stolons more than perennial ryegrass. Tall fescue reduced percent kikuyugrass cover, number and spread of stolons, and biomass (compared to perennial ryegrass). The newer turf-type tall fescue cultivars ‘Bonsai,’ ‘Falcon,’ and ‘Olympic’ were more effective than the older tall fescue cultivar ‘Fawn’ in reducing kikuyugrass invasion by reducing stolon number, stolon length, and biomass.

Glufosinate applied postemergence alone and in mixture with pendimethalin, thiobencarb, quinclorac, propanil, bensulfuron, bentazon, acifluorfen, or triclopyr was evaluated on bialaphosresistant (BAR) rice and red rice in field studies. Glufosinate at 2.2 kg ai/ha alone was less phytotoxic (6%) to BAR-transformed rice than when it was applied in combination with 0.4 kg ai/ha triclopyr (59%) or 0.6 kg ai/ha acifluorfen (22%). Rice yield with glufosinate alone was similar to the weed-free check the first year, but 13% less than the weed-free check the second year. For the glufosinate plus triclopyr mixture, rice yield was reduced by 39 and 76% compared with glufosinate alone in 1994 and 1995, respectively. Red rice control was 92% with either 3.4 kg ai/ha propanil or 0.6 kg/ha acifluorfen mixed with 0.6 kg/ha glufosinate, which was greater than for glufosinate alone and the other combinations. Propanil or acifluorfen mixed with glufosinate reduced red rice plant height, panicle maturity, and 100-seed weight 16, 31, and 24%, respectively, compared to glufosinate alone and 30, 48, and 43%, respectively, compared to the nontreated weedy check.