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.

Nicosulfuron is used with surfactant or oil adjuvant to enhance postemergence efficacy. Yellow foxtail fresh weight reduction from nicosulfuron varied from 10 to 92% depending upon surfactant in greenhouse experiments. Oil adjuvants differed in enhancement of nicosulfuron phytotoxicity to yellow foxtail or large crabgrass with methylated canola oil being most effective, followed by vegetable oils, and petroleum mineral oil as least effective. Percentage and type of surfactant used as an emulsifier in an oil adjuvant was important to nicosulfuron phytotoxicity especially when applied with the less effective oils, but was of minimal importance when applied with methylated canola oil. Adjuvant effectiveness was directly related to nicosulfuron absorption. These data indicated that recommendations for adjuvants to maximize nicosulfuron phytotoxicity should be limited to specific products.

In field experiments conducted near Marianna, Trenton, and Archer, FL in 1990 and 1991, nicosulfuron applied 55 weeks after planting (WAP) at 18, 27, 36, or 54 g ai/ha injured peanut initially. When applied 7 WAP, only the two higher nicosulfuron rates injured peanut more than 10%. By 6 wk after application, crop injury was less than 8% for all treatments, except the highest (54 g/ha) rate. Nicosulfuron applied 5 or 7 WAP at 54 g/ha reduced peanut yield and sound mature kernels.

Jointed goatgrass, downy brome, and horseweed are increasingly troublesome winter annual weeds during fallow periods in conservation-tillage systems in the southern Great Plains. These experiments determined the optimum weed size, vigor, and minimum herbicide rate required for 95% or better control of these weeds on fallow land. Jointed goatgrass and downy brome were controlled best when plants were 10 cm or less tall and growing vigorously at time of treatment. Horseweed was controlled best when plants were 30 cm tall and growing vigorously. Based on local retail and application costs and assuming optimum conditions for control, the two most economical herbicide treatments that controlled each weed 95% or better were: jointed goatgrass, clethodim at 250 g ai/ha and glyphosate + 2,4-D at 249 + 479 g ae/ha; downy brome, quizalofop at 18 g ai/ha and glyphosate + 2,4-D at 582 + 950 g ae/ha; and horseweed, 2,4-D at 560 g ae/ha and metsulfuron at 5 g ai/ha.

Field research was conducted to determine the effectiveness of DPX-79406 (a 1:1 mixture of nicosulfuron and rimsulfuron) for green foxtail control in field corn. Green foxtail control was similar when DPX-79406 was applied postemergence compared to preplant incorporated EPTC/dichlormid or metolachlor. DPX-79406 gave similar green foxtail control to that of cyanazine and better control than inter-row cultivation following soil-applied herbicides. Green foxtail control was greatest when DPX-79406 was applied at the one- to two-tiller stage compared to the one- to two-leaf stage, suggesting that green foxtail is more susceptible to DPX-79406 at later growth stages. DPX-79406 injured ‘Pioneer 3995’ corn in all trials but injured ‘Pride K020’ corn in only one treatment. DPX-79406 between 15 and 25 g ai/ha gave 85% control of green foxtail with minimal corn injury. Adjuvants tended to increase both corn injury and green foxtail control with Scoil and Merge increasing DPX-79406 activity the most. DPX-79406 provides an effective postemergence alternative for green foxtail control in field corn, for either preplant incorporated herbicides or postemergence cyanazine.

Greenhouse studies were conducted to determine the response of six corn hybrids and two soybean varieties to acetolactate synthase (ALS) inhibitor herbicides applied with terbufos and/or piperonyl butoxide (PBO), a mixed function oxidase (MFO) inhibitor. Field experiments also were conducted to determine the response of six corn hybrids to the combination treatments, terbufos plus ALS inhibitor herbicides and/or PBO and/or antidote. PBO at 0.33 kg/ha tank-mixed with nicosulfuron and primisulfuron injured the Northrup King 9283 corn hybrid. Great Lakes 584 corn was less sensitive than Northrup King 9283 to these combination treatments. Pioneer 3377 IR corn hybrid was resistant to the combination of nicosulfuron or primisulfuron plus PBO at 2 kg/ha and also to the combination treatments of imazethapyr herbicide plus PBO even though terbufos was previously applied. ICI 8532 IT, ICI 8532, and Pioneer 3377 hybrids were injured by the combination of nicosulfuron or primisulfuron and/or terbufos and/or PBO at 2 kg/ha. ICI 8532 IT corn hybrid was not injured by the combination treatment of imazethapyr or thifensulfuron and terbufos. In the field studies, Pioneer 3377 IR and Ciba 4393 RSC hybrids were resistant to sulfonylurea and imidazolinone herbicides even when applied with PBO regardless of the presence of terbufos. All treatments of chlorimuron plus terbufos caused considerable injury to ICI 8532 IT, ICI 8532, Pioneer 3377, and Ciba 4393, but not Pioneer 3377 IR and Ciba 4393 RSC. The combination of thifensulfuron with PBO injured Elgin ‘87 soybean, but the W20 soybean was tolerant to this combination treatment. Combination of imazethapyr with PBO did not affect the growth of Elgin ‘87 soybean.

Growth, seed production, and dormancy of velvetleaf in response to shading were evaluated in the field. Velvetleaf plant height, leaf number, number of branches, and plant dry weight decreased linearly with increasing shade. No differences were observed for plant height, number of leaves, or branches/plant when plants were shaded 30% or not shaded throughout the growing season. However, the 76% shade treatment reduced velvetleaf height (1984 only), leaf number, stem branches, and plant dry weight. These reductions were greater in 1984 than 1985 except for plant dry weight that decreased by 88% each year. The number of capsules and the number of seeds/plant decreased linearly with increasing shade levels, while the seed weight increased with increasing shade level. Shading also decreased seed dormancy. These results demonstrate that shade suppresses velvetleaf growth and seed production, and shortens the dormancy of seeds that are produced by these plants.

Glyphosate and package mixtures of glyphosate plus dicamba or 2,4-D were evaluated for the selective control of jointed goatgrass and downy brome in seeded perennial grasses. Glyphosate at 560, glyphosate plus dicamba at 550 + 220, and glyphosate plus 2,4-D at 420 + 350 and 570 + 470 g ai/ha controlled 90% or more jointed goatgrass in 1988 and 1991. Glyphosate plus 2,4-D at 150 + 120 and 280 + 240 g/ha were the only treatments that controlled less than 90% of jointed goatgrass in 1991. In 1988, glyphosate at 210 g/ha and glyphosate plus dicamba at 210 + 80 g/ha were the only treatments that controlled less than 90% of downy brome. Glyphosate at 210, 280, 420, and 560 g/ha, glyphosate plus dicamba at 210 + 80, 280 + 110, 420 + 170, and 550 + 220 g/ha, and glyphosate plus 2,4-D at 150 + 120, 280 + 240, 420 + 350, and 570 + 470 g/ha controlled 90% or more downy brome in 1990. Pubescent wheatgrass and crested wheatgrass were stunted or killed if they were growing when herbicides were applied.

Field experiments were conducted to evaluate postplant crop residue, green and yellow foxtail control, and wheat grain yield after fall application of trifluralin granules in undisturbed small grain stubble. Levels of postplant residue were at least 48% cover (line transect method) and 2750 kg/ha of aboveground dry matter where herbicide granules were left unincorporated or were incorporated with conservation-till methods, including an undercutter, rotary hoe, or undercutter followed by a rotary hoe. Trifluralin at 0.56 kg/ha applied as granules in mid October in untilled stubble and incorporated with conservation-till methods controlled foxtail 81 to 88%, with control appearing slightly lower when granules were not incorporated. The 81 to 88% foxtail control in conservation-till treatments was comparable to control achieved with trifluralin at 0.56 kg/ha applied in mid October on conventionally-tilled soil and incorporated by a field cultivator. Foxtail control improved somewhat as trifluralin rate was increased to 0.84 and 1.12 kg/ha in conservation-till treatments. Slight wheat stand reductions at 1.12 kg/ha of trifluralin did not appear to reduce wheat yield. Fall application of trifluralin granules in these high-residue conditions apparently minimizes herbicide losses by photodecomposition and volatility, thereby facilitating good trifluralin efficacy the following season.

Field experiments were conducted in Tifton, Midville, and Athens, GA to determine economic net returns from PRE-broadcast, PRE-banded, POST, and POST-directed herbicide treatments and inter-row cultivation in conventional-tillage soybean. Metribuzin applied PRE-broadcast was more effective for sicklepod and morningglory control than PRE-banded. Soybean net returns were not significantly reduced in two of three years in plots treated with metribuzin applied PRE-banded compared with broadcast application. The addition of POST or POST-directed herbicides increased treatment net returns over PRE-broadcast and PRE-banded metribuzin two of the three years of the study. No significant soybean injury was observed.

Greenhouse and field experiments were conducted from 1987 to 1990 at the Lacombe Research Station to determine the influence of ammonium sulfate (AS) on various grass control herbicides. In field studies, AS had slight or no effects on the phytotoxicity of aryloxyphenoxypropanoate (APP) herbicides (fenoxaprop, fluazifop, haloxyfop, and quizalofop). The largest AS-mediated increase in APP herbicide phytotoxicity was 19% (based on fresh weight reduction) for wild oat with haloxyfop at 50 g/ha. AS consistently mediated increases in cyclohexanedione (CHD) herbicide phytotoxicity. With added AS, barley fresh weight was reduced 75% (1988) with BAS 517 at 50 g/ha, and 100% (1990) with clethodim at 25 g/ha. Greenhouse studies confirmed field studies, but differences were less substantial and consistent. It is suggested that APP herbicides are either less susceptible to UV degradation than CHD herbicides, and/or that APP herbicides may penetrate plant cuticles quickly enough to nullify any protection from UV degradation that AS might provide via rapid absorption.

R230, an isolate of Rhizoctonia solani anastomosis group 5 from leafy spurge, caused root and crown rots on leafy spurge when inoculated via soil in greenhouse experiments. The fungus grew through soil over a wide range of matric potentials (–0.01 to −1 MPa). When applied to leafy spurge foliage, the fungus blighted young adventitious shoots, but not mature stems. Foliar infection required high relative humidity. Mycelial growth on plant surfaces stopped at below 92% relative humidity. Pathogenicity of R230 was not limited to leafy spurge. The fungus caused stem and foliar lesions on all crops tested (alfalfa, smooth bromegrass, corn, Kentucky bluegrass, soybean, tall fescue, and wheat) when plants were kept under high humidity. It reduced seedling emergence and survival in soybean, Kentucky bluegrass, and tall fescue. R230 also caused a foliar blight on spotted spurge. The potential for R230 to damage crops will limit application of the fungus to noncultivated areas and to sites where it is endemic.

In comparing laboratory techniques, absorption and translocation of 14C-haloxyfop was not affected by droplet size or treatment area. Treatment with haloxyfop prior to application of 14C-haloxyfop resulted in 27% less translocation of radiolabel from the treated leaf and 43% less acropetal translocation compared with plants receiving only the radiolabeled herbicide. Leaf washing with distilled water, distilled water plus haloxyfop, distilled water plus surfactant, distilled water plus haloxyfop plus surfactant, 100% ethanol, 100% methanol, or methanol:water (1:1 v/v) removed similar amounts of radiolabel, while chloroform removed more. Considering some of the differences found with these techniques, pretreatment with nonlabeled herbicide should be routine practice and water used as the standard solvent.

Two furrow irrigated field experiments were conducted for two years at the Research and Extension Center, Powell, WY to determine the influence of various mixed densities and durations of wild oat and wild mustard interference in sugarbeet. Sugarbeet root yields were reduced by competition from all examined densities of wild oat and wild mustard, alone and in combination. Root yield reduction was less than additive with mixed densities of wild oat and wild mustard. Root yields decreased as the duration of interference after sugarbeet emergence from a mixed density of wild oat and wild mustard increased. Sucrose content of sugarbeet was not altered by competition. Based on regression analysis, the minimum time that a mixed density of 0.8 wild mustard and 1 wild oat/m of row can interfere with sugarbeet before causing an economic root yield loss was approximately 1.6 weeks after sugarbeet emergence.

Field experiments were conducted at the Lacombe Research Station from 1989 to 1991 to determine if short-term, split applications of grass-specific herbicides would improve quackgrass control relative to single applications. Quackgrass infested plots were planted to canola the first year and barley the following year. Glyphosate applied at 880 g/ha controlled quackgrass to a greater extent and for a longer time period than any of the grass-specific herbicides. In contrast to glyphosate, none of the grass-specific herbicides controlled quackgrass 1 yr after treatment. Quackgrass control with sethoxydim or fluazifop-P was usually similar when applied as single or short-term, split applications. In contrast, quizalofop often provided better quackgrass control and higher crop yields when short-term, split applications were compared to a single application with the same total amount of quizalofop. However, the extent of increased quackgrass control is difficult to justify due to increased application costs and inconvenience.

Optimal time of application of the isopropylamine salt of glyphosate for long-term control of foxtail barley was studied near Delta Junction, AK in 1992 and 1993. Applications of either 0.6 or 1.1 kg/ha of glyphosate with 2.2 kg/ha of ammonium sulfate and 0.5% (v/v) nonionic surfactant were made to different foxtail barley plots at approximately 2-wk intervals from May to September. Control was rated in July of the year following application. The 0.6 kg/ha rate produced ≤ 60% control on all application dates. At 1.1 kg/ha, foxtail barley control was best from applications made between early August and mid-September. May and mid-June applications provided up to 80% control in 1993 but ≤ 50% control in 1992. For both rates, applications made from late June through July, during foxtail barley flowering and seed fill, consistently provided little control (< 50%).

Field studies were conducted in 1990 and 1991 to evaluate johnsongrass control and interference in corn using combinations of nicosulfuron, EPTC + dichlormid, and cultivation. Nicosulfuron applied to 30-cm-tall rhizome johnsongrass provided greater control and corn yield than a later application to 60-cm-tall johnsongrass. Johnsongrass control and corn yield within the later nicosulfuron treatment were improved by a preplant application of EPTC. EPTC and/or cultivation alone provided less johnsongrass control and lower corn yield than nicosulfuron or handweeding.

Four broadleaf herbicides and combinations were compared for two years with mefluidide, a growth regulator, for effects on ‘Ky 31’ and ‘Fawn’ tall fescue. Seedhead densities averaged 33% of the check with 8.4 g ai/ha of metsulfuron, 17% with 70 g ai/ha of imazethapyr, and 9% with 280 g ai/ha of mefluidide, while forage yields were reduced to about 40% of the check. Forage crude protein (CP) concentrations were increased by mefluidide, imazethapyr, and 8.4 g/ha of metsulfuron. Neutral-detergent fiber (NDF) of Ky 31 but not Fawn forage was reduced by mefluidide, imazethapyr, and metsulfuron at 6.3 and 8.4 g/ha, but Fawn NDF was increased by dicamba plus 2,4-D. In vitro dry matter digestibility was increased by metsulfuron at 6.3 and 8.4 g/ha, mefluidide, and imazethapyr in one of two years. Adding 2,4-D to metsulfuron reduced some effects of metsulfuron. Total CP/ha was no more adversely affected by imazethapyr and metsulfuron than mefluidide. Imazethapyr and metsulfuron can thus be used to control weeds without reducing fescue forage value.

A field experiment was conducted over a 2-yr period to determine the effects of reduced PRE herbicide rates on large crabgrass infestation in six tall fescue cultivars. With the exception of oryzalin and benefin plus oryzalin in 1993, there was no cultivar by herbicide interaction for large crabgrass infestation when final ratings were made in 1993 and 1994. This interaction was caused by moderate to severe turfgrass injury that thinned the turf. When cultivars were disregarded, prodiamine was the only herbicide applied at one-third recommended rate in 1993 that effectively suppressed large crabgrass for the full season. Prodiamine and dithiopyr were the only PRE herbicides applied at one-third recommended rates for two consecutive years that effectively suppressed large crabgrass in 1994. Two-thirds recommended rate was needed for two consecutive years for oxadiazon, pendimethalin, oryzalin, benefin plus oryzalin, and benefin plus trifluralin to maintain optimum large crabgrass suppression in 1994.

Greenhouse and field studies were conducted in 1992 and 1993 in Manitoba and Saskatchewan to determine the effect of simulated sprayer contamination with thifensulfuron and thifensulfuron:tribenuron (2:1) on canola. In greenhouse studies, canola was more sensitive to tribenuron and thifensulfuron:tribenuron (2:1) than thifensulfuron. Thifensulfuron was more phytotoxic to canola when applied with Merge (50% surfactant blend and 50% petroleum hydrocarbon solvents) than with Agral 90 (non-ionic spreader and activator) at recommended adjuvant concentrations {1% and 0.2% (v/v), respectively}. In the field, canola injury tended to be more severe when thifensulfuron was applied with Merge than with Agral 90, but yields did not differ significantly between adjuvants, Thifensulfuron and thifensulfuron:tribenuron (2:1) at rates as low as 0.1 g ai/ha severely injured canola, delayed flowering, and reduced yield and subsequent seed germination. Thifensulfuron at 0.1 to 0.15 g/ha in mixtures with sethoxydim plus Merge reduced yields up to 61%.