bluuebunny/crossref_metadata_2025 huggingface dataset:
Woolly Cupgrass (Eriochloa villosa) Control in Corn (Zea mays) with Pendimethalin/Triazine Combinations and Cultivation
Authors: Schuh Joseph F. , Harvey R. Gordon
Published: May 2019

In 1985, 1986, and 1987, pendimethalin at 1.7 kg ai/ha plus 2.2 kg ai/ha cyanazine, 2.2 kg ai/ha atrazine, or 1.1 kg/ha atrazine plus 1.1 kg/ha cyanazine was applied delayed preemergence, early postemergence, and postemergence with and without cultivation to evaluate woolly cupgrass control and corn injury. Results varied from year to year. Dry conditions in 1985 resulted in poorer woolly cupgrass control while cold and wet environments in 1987 resulted in corn injury and reduced yields from postemergence treatments containing cyanazine. Good early-season suppression of woolly cupgrass deteriorated to less than 75% control by the late-season evaluation in all experiments. The best woolly cupgrass control and highest corn yields were usually achieved when herbicide applications were followed by row cultivation. Corn yield increases averaged 28, 17, and 11% in 1985, 1986, and 1987, respectively, when a herbicide treatment was followed by row cultivation. Pendimethalin/triazine treatments followed with a row cultivation adequately suppressed woolly cupgrass in field corn, but adverse environmental conditions often reduced herbicide effectiveness or increased corn injury.
Soil Residual Properties of DPX-A7881 Under Laboratory Conditions
Authors: Beckie Hugh J. , McKercher Robert B.
Published: May 2019

Growth chamber studies were conducted to examine the soil residual properties of DPX-A7881, a new sulfonylurea herbicide. The phytotoxic residue levels in the soil were determined by a lentil radicle bioassay. The duration of activity was prolonged in soil adjusted to pH 7.6 and 8.1 relative to more acidic levels. The rate of breakdown in the soil was enhanced with increased temperature and soil moisture content; a significant temperature by moisture interaction was noted over the duration of the incubation period. The dissipation of DPX-A7881 in soil obeyed first-order kinetics in both studies. An accelerated rate of breakdown in unsterilized versus sterilized soil (pH 7.6) indicated that microbial degradation was an important factor affecting the persistence in alkaline soils. Herbicide residues in the soil caused a reduction in taproot length and number of primary lateral roots of canola seedlings 15 days after planting but there were no other morphological effects observed on the root. The secondary laterals, however, had generally recovered by this time.
Phytotoxicity, Adsorption, and Mobility of Metribuzin and Its Ethylthio Analog as Infuenced by Soil Properties
Authors: Peek Daniel C. , Appleby Arnold P.
Published: May 2019

The phytotoxicity, adsorption, and mobility of metribuzin and ethyl-metribuzin3were studied in five soils to determine if differential soil behavior could explain: a) the greater activity of both chemicals in western Oregon than in eastern Oregon, and b) the greater activity of metribuzin than ethyl-metribuzin under similar conditions. Metribuzin had higher activity on oats than ethyl-metribuzin in all soils and in quartz sand. Metribuzin was adsorbed less and moved more than ethyl-metribuzin in all soils. Activity of both herbicides decreased as sand content increased, and activity in quartz sand was lower than in soil. Activity of both herbicides increased in a bioassay in which leaching was prevented, indicating that leaching may be important in the loss of activity of metribuzin and ethyl-metribuzin. Lowest herbicide adsorption and greatest movement were observed in coarser textured soils.
Bacterial Stimulation by Carbamothioate Herbicides
Authors: Mueller James G. , Skipper Horace D. , Lawrence Ernest G. , Kline Ellis L.
Published: May 2019

Laboratory studies enumerated butylate-, EPTC-, vernolate-, pebulate-, and cycloate-utilizing bacteria and actinomycetes in a Dothan loamy sand following repeated use of butylate, EPTC, or vernolate. Herbicide utilizers were isolated on a defined medium composed of minimal salts plus 200 mg/L herbicide as the primary carbon source plus 25 mg/L TTC as an indicator of organisms capable of metabolizing the herbicide substrates. Media inoculated with a butylate-history soil developed more TTC-red actinomycetes on the butylate-indicator agar than did media inoculated with a non-herbicide-history soil. Similarly, media inoculated with a vernolate-history soil developed more TTC-red bacteria on the vernolate-indicator agar. Cross-adaptation from vernolate to butylate and cycloate was evident, with inoculant from the vernolate-history soil exhibiting an increase in bacterial counts when butylate or cycloate was present as the primary carbon source. Likewise, previous butylate exposure corresponded with an increase in the number of vernolate- and pebulate-utilizing actinomycetes. Previous exposure to EPTC resulted in an increased population of butylate- and pebulate-utilizing actinomycetes.
Sorption and Mobility of Chlorimuron in Alabama Soils
Authors: Goetz Andrew J. , Walker Robert H. , Wehtje Glenn , Hajek Ben F.
Published: May 2019

Soil thin-layer chromatography and a soil solution technique were used to evaluate chlorimuron adsorption and mobility in five Alabama soils. The order of adsorption was atrazine > metribuzin > chlorimuron; mobility was chlorimuron > metribuzin > atrazine. The order of adsorption of chlorimuron in the five soils was Sumter clay > Eutaw clay > Lucedale fine sandy loam > Decatur silt loam > Dothan sandy loam, and Rfvalues were 0.63, 0.73, 0.69, 0.76, and 0.80, respectively. Chlorimuron mobility and adsorption were not highly correlated to any one soil type. Adsorption of all herbicides was inversely related to soil pH. Maximum chlorimuron adsorption in the Hiwassee loam was attributed to the high hematite and gibbsite content of the soil.
Fate of14C-EPTC in a Soil Exhibiting Accelerated Degradation of Carbamothioate Herbicides and Its Control
Authors: Tal Abraham , Rubin Baruch , Katan Jaacov , Aharonson Nadav
Published: May 2019

Laboratory experiments were conducted to determine the fate of14C-EPTC in a soil that had a history of vernolate application and exhibited accelerated degradation of carbamothioate herbicides compared to nonhistory soil. A very rapid mineralization of the herbicide to14CO2was evident in history soil, compared to nonhistory soil. The two soils did not differ in the amounts of the EPTC lost through volatilization or in the nonextractable radioactive fractions. Except for small quantities of EPTC-sulfoxide and sulfone, no other metabolites were detected. Degradation of14C-EPTC, as determined by evolution of14CO2in history soil, was drastically inhibited following soil sterilization by means of autoclaving or gamma irradiation. Soil disinfestation by solarization, methyl bromide, or metham had a pronounced inhibitory effect during the first 6 days, but was less effective than sterilization. Treatment of a history soil with the fungicide 2-methoxyethylmercury chloride and dietholate strongly inhibited EPTC degradation, while thiram and fentin acetate had only short lasting effects. Cycloheximide, an antifungal antibiotic, had little effect on the degradation of EPTC while chloramphenicol, an antibacterial antibiotic, inhibited the herbicide degradation. These results indicate that accelerated degradation of EPTC is linked to the activity of soil microorganisms, e.g. bacteria, and can be controlled by sterilization and chemical treatments.
Adsorption of Clomazone on Soils, Sediments, and Clays
Authors: Loux Mark M. , Liebl Rex A. , Slife Fred W.
Published: May 2019

Regression analysis of clomazone adsorption on 19 soils and sediments yielded a positive correlation and linear relationship between distribution adsorption constants (Kd) and soil organic carbon content. The agreement of the experimental mean Kocwith Kocvalues predicted from the octanol-water partition coefficient and water solubility of clomazone indicated hydrophobic bonding was one mechanism responsible for adsorption. Kaolinite and montmorillonite had a strong affinity for clomazone, and adsorption increased with the charge of the cation on the clay exchange sites. Adsorption was not correlated with the clay content of soils and sediments, indicating that organic coatings on clay in soils may block adsorption sites on clay surfaces. The adsorption of clomazone on some soils and sediments with high clay contents was greater than predicted based on organic carbon content alone, however, indicating clay contributed to adsorption on these samples.
Effects of Chlorsulfuron onRhizobiumGrown in Pure Culture and in Symbiosis with Alfalfa (Medicago sativa) and Red Clover (Trifolium pratense)
Authors: Mårtensson Anna M. , Nilsson Åsa K.
Published: May 2019

The effect of chlorsulfuron on growth, infective ability, and symbiotic performance of legume bacteria was investigated. Bacterial growth in pure culture was unaffected by the addition of 0.55 and 5.5 μM chlorsulfuron. Early root hair infections of alfalfa by bacteria were inhibited by chlorsulfuron at 0.28 pM but not at 0.0028 pM in the root media. Inhibition of infection resulted from herbicidal effects on the root hair development. When inoculated red clover and alfalfa plants were grown in aseptic cultures in the presence of 0, 5.5, or 55 μM of chlorsulfuron, only 55 μM of herbicide inhibited the development and nodulation of plants. Early emergence and growth of alfalfa plants in soil supplemented with 2 × 10-6, 2 × 10-3, 2, 4, and 8 g/ha of chlorsulfuron were unaffected. However, 5 to 8 days after emergence plants grown in soil supplemented with 4 or 8 g/ha of chlorsulfuron were severely damaged, with no nodules developed. Nodulation occurred in plants grown in soil containing 2 × 10-3, 3 × 10-6, and 2 g/ha chlorsulfuron, but the nitrogenase activity of the nodules of these plants was less than for control plants. Plants grown in soil containing 2 g/ha of chlorsulfuron developed normally only after an initial growth inhibition of 5 to 6 weeks. The inhibition of nodulation and nitrogenase activity of nodules grown in the presence of chlorsulfuron is probably due to adverse effects of the herbicide on plant growth and development rather than on the rhizobia.
Predicted Evolutionary Response to Selection for Tolerance of Soybean (Glycine max) and Intraspecific Competition in a Nonweed Population of Poorjoe (Diodia teres)
Authors: Jordan Nicholas
Published: May 2019

Genetic variation within a nonweed (coastal) population of poorjoe was measured in an experimental population subjected to soybean and intraspecific competition for space and light. A sib analysis was used to estimate phenotypic and genetic variance/covariance components of aboveground biomass production and five independent measurements of growth defined by a path-coefficient model. A multivariate analysis of response to selection was applied to predict evolutionary change in the growth measurements in response to selection for performance under soybean and intraspecific space/light competition; sufficient genetic variation was present in the experimental population to allow a rapid response to this selection. Selection under competitive conditions was predicted to cause the nonweed population to emerge earlier, grow faster early in development, change in growth form, and grow faster under a soybean canopy. Most of these changes would increase the resemblance of the selected population to a weed population of poorjoe. However, the growth rate of the selected population under a soybean canopy was predicted to become greater than that actually observed in the present-day weed population. Multivariate analysis of response to selection may be generally useful in predicting evolutionary response of plant pest populations to control practices.
A Population Level Temperature-Dependent Model of Seedling Johnsongrass (Sorghum halepense) Flowering
Authors: Bridges David C. , Chandler James M.
Published: May 2019

A population level, two-compartment, temperaturedependent model that predicts date of seedling johnsongrass flowering was formulated. The model consisted of a fourparameter poikilotherm rate equation to describe development rate as a function of temperature and a temperature-independent Weibull function to distribute flowering times for the population. Experiments were conducted to determine the effect of temperature, nitrogen availability, and water availability on development of seedling johnsongrass. Development was most sensitive to temperature while the effect of nitrogen concentration and water availability was minimum and inconsistent. The model was tested against three independent field data sets and provided accurate prediction of flowering dates for each data set.
Thidiazuron andColletotrichum coccodesEffects on Ethylene Production by Velvetleaf (Abutilon theophrasti) and Prickly Sida (Sida spinosa)
Authors: Hodgson Richard H. , Snyder Robert H.
Published: May 2019

The effects of the plant growth regulator thidiazuron and the plant pathogenColletotrichum coccodeson ethylene synthesis by velvetleaf and prickly sida were investigated. Untreated velvetleaf seedlings produced 1.5 and 2.3 pmol ethylene/mg fresh weight 24 and 48 h after treatment. Treatment with thidiazuron at 200 g ai/ha orC. coccodesat 1 × 109spores/m2increased ethylene production by 4.9 and 3.5 pmol/mg, respectively, in 24 h; and by 10.6 and 15.8 pmol/mg, respectively, in 48 h. Combination treatments caused synergistic increases in ethylene production by velvetleaf seedlings of 17.7 and 49.6 pmol/mg in 24 and 48 h, respectively. Thidiazuron at 10 μM, combined with an extract ofC. coccodesmycelia, increased ethylene synthesis by more than 4-fold in vacuum-infiltrated excised velvetleaf petioles within 48 h. Thidiazuron at 50 g/ha, combined with an extract ofC. coccodesmycelium, increased ethylene synthesis 16-fold in prickly sida seedlings in 24 h. Aminocyclopropane carboxylic acid (ACC), a precursor of ethylene, stimulated ethylene production by velvetleaf petioles more than 8-fold when supplied at 0.75 mM; thidiazuron and the pathogen effects were not discernible in its presence. Aminoethoxyvinyl-glycine (AVG), an inhibitor of ACC synthase, inhibited overall ethylene production by velvetleaf seedlings more than 40% when supplied at 0.58 to 0.67 mM, without obscuring the stimulatory effects of thidiazuron and the pathogen. These results indicate that the growth regulator and the plant pathogen or an extract of the pathogen act in concert to increase ethylene synthesis in velvetleaf. Stimulation probably occurs before the synthesis of ACC in the ethylene biosynthetic pathway.
Biochemical Interactions of Atrazine and Glyphosate in Soybean (Glycine max) Seedlings
Authors: Hoagland Robert E
Published: May 2019

Laboratory studies were conducted to evaluate possible interactions of atrazine and glyphosate on soybeans at the molecular level. Because these compounds alter the extractable activities of nitrate reductase (NR)3and phenylalanine ammonia-lyase (PAL), these enzymes were chosen as biochemical markers. Levels of anthocyanin, hydroxyphenolic compounds, and chlorophyll were also determined. Three-day-old dark-grown soybean seedlings, susceptible to both herbicides, were transferred to 2 mM CaSO4or CaSO4containing high-purity 10–4M atrazine, 10–4M glyphosate, or a combination of both herbicides at 10–4M each. Plants were placed in a growth chamber under continuous light (200 μE·m–2·s–1) at 25 C and harvested at 24-h intervals over a 96-h time course. Interactions of atrazine and glyphosate on hypocotyl elongation were detected after 96 h when the compounds were supplied simultaneously. Intermediate PAL levels were found in the atrazine + glyphosate treatment compared to the levels for each herbicide alone. At 96 h, anthocyanin content in hypocotyls in the atrazine + glyphosate treatment was twice that of the atrazine treatment, and hydroxyphenolic content was increased by 25% (per axis). Interactions of these herbicides were also apparent on NR activity; i.e., on a per organ basis the combination treatment resulted in levels 20% higher than glyphosate alone in roots and 16 times greater than glyphosate alone in leaves after 96 h. Total chlorophyll content in hypocotyls (μg/organ) was decreased by atrazine but not significantly by glyphosate after 96 h. Atrazine + glyphosate resulted in chlorophyll content equal to that of atrazine alone. Mathematical analyses showed that interactions on NR, PAL, anthocyanin levels, and hypocotyl elongation were antagonistic at 96 h. These data demonstrate interaction between atrazine and glyphosate in plant tissues that is related to some biochemical parameters associated with the secondary molecular mode of action of these herbicides.
Absorption, Translocation, and Metabolism of Picloram and 2,4-D in Leafy Spurge (Euphorbia esula)
Authors: Lym Rodney G. , Moxness Kevin D.
Published: May 2019

The absorption, translocation, and metabolism of14C-picloram and14C-2,4-D applied alone and together to leafy spurge was evaluated. Leafy spurge absorbed 34 and 24% of the14C-2,4-D applied alone and with picloram, respectively, and 14 and 10% of the14C-picloram applied alone and with 2,4-D, respectively. More14C-2,4-D was translocated in leafy spurge than14C-picloram, and adding picloram to14C-2,4-D decreased14C translocation to the roots. Adding 2,4-D to14C-picloram increased the percentage of absorbed14C that translocated in leafy spurge from 28 to 48%. Generally,14C-picloram and14C-2,4-D remained as the parent acid in leafy spurge whether applied alone or together. Of14C-picloram recovered from the roots, 83% was unmetabolized picloram when applied alone compared to 95% when applied with 2,4-D, which probably is the reason for increased leafy spurge control when these herbicides are applied together.
Mechanism of Synergism Between Metribuzin and MZH 2091 on Ivyleaf Morningglory (Ipomoea hederacea)
Authors: Klamroth Eva E. , Fedtke Carl , Kühbauch Walter C.
Published: May 2019

Experiments were conducted in order to establish the mechanism by which the synergist MZH 2091 increases metribuzin activity on ivyleaf morningglory. Herbicide absorption and metabolism were compared for plants treated either with14C-metribuzin alone or with14C-metribuzin plus nonlabeled MZH 2091. The compounds were applied via the roots for 3 h and the absorption was determined. After the pulse treatment, the plants were grown for additional 0, 3, 6, 9, 12, 21, 45, or 69 h in water, and the metribuzin metabolism was studied in the cotyledons. The synergist did not interfere with herbicide uptake but did strongly inhibit metribuzin metabolism. The pathway of metribuzin metabolism in ivyleaf morningglory is discussed as well as the way it is affected by the synergist MZH 2091.
Developmental Rates of Wild Oats (Avena fatua) and Wheat (Triticum aestivum)
Authors: Cudney David W. , Jordan Lowell S. , Corbett Chris J. , Bendixen Warren E.
Published: May 2019

Prediction of the developmental stages of wheat and wild oats would be useful in order to: 1) correctly time the application of herbicides, and 2) accurately schedule research and cultural operations. The Haun developmental scale which numbers leaf development and describes floral development on the main stem of grasses was found to be suitable for describing the development of semidwarf wheat and wild oats in California. Haun developmental rates of wheat and wild oats were similar. Interference by wheat or wild oats in mixed cultures did not change the developmental rate of either species when grown with added nutrients and water. Degree days gave better correlations with development than calendar days when different planting dates, years, and locations were compared. A degree day model with a 5 C base temperature and a second-order polynomial expression gave accurate predictions of developmental stage, which correlated well with field data.
Influence of Moisture Deficits on the Reproductive Ability of Downy Brome (Bromus tectorum)
Authors: Richardson Jesse M. , Gealy David R. , Morrow Larry A.
Published: May 2019

Downy brome seed production was measured in the field following the establishment of different moisture levels using a line source sprinkler irrigation system. Results indicated that seed production was strongly affected by different moisture levels, with a curvilinear decrease in seed number from higher to lower moisture. In a hydroponic study with water deficits induced by PEG-8000, no seeds were produced when plants were severely stressed (-1.1 MPa) for a 7-day period during culm elongation or anthesis. Number of seeds/panicle was reduced under severe water stress during seed fill, under moderate stress (-0.5 MPa) during anthesis or seed fill, and under mild stress (-0.1 MPa) during anthesis. Water stress also reduced apparent photosynthesis and increased diffusive resistance of flag leaves, particularly under severe stress. In general, water deficits did not affect seed weights or germination percentages in either study.
Competitive Interactions of Wheat (Triticum aestivum) and Wild Oats (Avena fatua) Grown at Different Densities
Authors: Cudney David W. , Jordan Lowell S. , Holt Jodie S. , Reints John S.
Published: May 2019

Competitive interactions of wheat and wild oats in relation to variations in plant density of both species were investigated in field studies under irrigation and added fertilizer. Competition studies included comparisons by both additive and replacement series. The additive series was used to study plant responses to competition under fixed density of wheat and increasing density of wild oats. The replacement series was used to study plant responses to competition under constant total plant density with differing proportions of wheat and wild oats. On a per plant basis, shoot dry weight and leaf area index of wild oats were less than those of wheat at anthesis. However, the replacement series experiment indicated that wheat and wild oats were equivalent in competitiveness. Relative density of wild oats gave a better regression fit for wheat yield than did absolute wild oats density (r2values of 0.83 and 0.61, respectively). Yield of wheat grain was linearly proportional to relative density of wild oats.
The Influence of Water Stress on the Physiology and Competition of Soybean (Glycine max) and Florida Beggarweed (Desmodium tortuosum)
Authors: Griffin Blair S. , Shilling Donn G. , Bennett Jerry M. , Currey Wayne L.
Published: May 2019

Replacement studies were conducted under greenhouse conditions to determine if available soil water influences the competitive interaction between soybean and Florida beggarweed. Stomatal conductance and leaf water potential were determined for both species under different levels of available soil water to identify possible mechanisms involved in changes in the relative competitiveness induced by the water deficits. Soybean leaf area and aboveground biomass were greater than for Florida beggarweed under optimum water, but equal to or less than Florida beggarweed with water stress. Soybean was more competitive than Florida beggarweed when there was adequate soil water but less competitive than Florida beggarweed under water stress. Stomatal conductance was higher for soybean with optimum soil water (at high leaf water potentials) but equal to Florida beggarweed as soil water became limiting (low leaf water potentials). These data indicated that water stress differentially affected soybean and Florida beggarweed.
Differential Responses to Photoperiods in Monoecious and DioeciousHydrilla verticillata
Authors: Van Thai K.
Published: May 2019

Growth and morphology of two U.S. hydrilla biotypes grown under 10- and 16-h photoperiods in outdoor aquaria were investigated. The dioecious hydrilla biotype elongated extensively under both photoperiods and reached the water surface within 2 to 3 weeks after planting. In contrast, the monoecious biotype grew more densely near the sediment, primarily by producing a high number of horizontal stems, root crowns, and higher shoot densities. Monoecious hydrilla grown from tubers produced new tubers after 4 weeks of exposure to the 10-h photoperiod, and the number of tubers produced was five- to sevenfold higher in the monoecious than in the dioecious biotype. Furthermore, monoecious hydrilla produced tubers under both 10- and 16-h photoperiods, with tuber production much higher under the shorter photoperiod. Dioecious hydrilla grown from tubers under similar conditions produced new tubers after 8 weeks only under the 10-h photoperiod. No tubers were produced by the dioecious biotype throughout a 10-week exposure to the 16-h photoperiod.
Influence of Planting Date on Growth of Barnyardgrass (Echinochloa crus-galli)
Authors: Keeley Paul E. , Thullen Robert J.
Published: May 2019

Barnyardgrass seeded in field plots at monthly intervals from March through October at Shatter, CA, began to emerge in March when soil temperatures reached 17 C at a depth of 5 cm. For all plantings, most of the seeds germinated and produced seedlings within 2 weeks. Increasing day lengths favored vegetative growth, with April, May, and June plantings producing the tallest plants, the most dry matter, and the largest number of tillers. July and August plantings, the first to flower, began flowering and producing seeds within 5 to 6 weeks after planting, but the greatest number of seeds (15 000 to 25 000/plant) was produced by the larger plants of the April, May, and June plantings. September plantings produced few seeds/plant (37), when compared to March (5900), July (9800), and August (9700) plantings. The earliest that seed production would be expected from seedlings emerging in March and April would be early June, and seedlings emerging in September could produce seeds before killing frosts.
Response of Soybeans (Glycine max) and Four Broadleaf Weeds to Reduced Irradiance
Authors: Stoller Edward W. , Myers Randy A.
Published: May 2019

Experiments were conducted to determine adaptation characteristics to reduced irradiance of velvetleaf, common lambsquarters, eastern black nightshade, tumble pigweed, and soybean. Plants were grown to the 5- to 8-leaf stage in the greenhouse at ambient radiation (850 μE·m–2·s–1), and 26 and 13% of ambient radiation. Tumble pigweed, a C4plant, had the highest light-saturated photosynthetic rates at all growth irradiances, while common lambsquarters had the highest rates of the four C3species. All species adjusted to reduced irradiance by decreasing light-saturated photosynthesis, leaf respiration rates, root:shoot ratios, and leaf densities, while increasing leaf area ratios (LAR)3. As growth irradiance was reduced, support tissues (roots, stems, and petioles):leaf ratios did not change for common lambsquarters or velvetleaf, increased for soybean, and decreased for eastern black nightshade and tumble pigweed, indicating superior adaptation of the latter two species for efficient light harvesting at reduced growth irradiances. Of these five species, eastern black nightshade had the lowest respiration rate, the highest LAR, and the lowest support:leaf ratio for optimum adaptation to shaded environments.
Morphological and Histological Effects of Three Grass Selective Herbicides on Developing Wild Oat (Avena fatua) Stems
Authors: Jain Rakesh , Vanden Born William H.
Published: May 2019

Three grass selective herbicides, sethoxydim, fluazifop, and haloxyfop, applied to wild oat plants at the five-leaf stage inhibited growth and induced chlorosis in leaves. Young and actively growing tissues were affected first. Stem elongation in wild oat was inhibited within 2 days of treatment with sethoxydim and within 5 days of treatment with fluazifop or haloxyfop. At these same observation times, internodes that were elongating rapidly at the time of treatment were constricted at the base. These symptoms were followed by necrosis of the internode tissue. Histological examination of the affected internodes indicated that the herbicides inhibited cell division in very young internodes and inhibited both cell division and cell elongation in slightly older internodes. Initial injury occurred in the epidermal, cortical, and procambium cells of the peripheral regions of the stems located at the base of the affected internodes. Necrosis then progressed to the center of the stem tissue and all cells in the internodes were killed within 14 days of treatment. All three herbicides caused similar morphological and histological effects on developing wild oat stems.
Application of Fluazifop-P, Haloxyfop, and Quizalofop by Sprinkler Irrigation
Authors: Guy Charles B. , Talbert Ronald E. , Ferguson James A. , Johnson David H. , McClelland Marilyn R.
Published: May 2019

In field studies, sprinkler irrigation application of the butyl ester of fluazifop-P, the methyl ester of haloxyfop, and the ethyl ester of quizalofop controlled large crabgrass as well as conventional spray applications. In greenhouse investigations, root uptake of the herbicides from sprinkler irrigation applications injured large crabgrass more than root uptake from conventional applications, but large crabgrass injury from shoot uptake was equal with sprinkler irrigation and conventional applications. Droplets with dilute concentrations of herbicide and crop oil, simulating sprinkler irrigation, were more active when applied to the whorl or second leaf than to the first leaf of large crabgrass. An increase in concentration of nonemulsified oil in the treatment solution increased herbicide deposition and retention.
Characterization of Triazine-Resistant Giant Foxtail (Setaria faberi) and its Control in No-tillage Corn (Zea mays)
Authors: Ritter Ronald L. , Kaufman Lisa M. , Monaco Thomas J. , Novitzky William P. , Moreland Donald E.
Published: May 2019

Triazine-resistant giant foxtail was identified in 1984 near Delta, PA. In field studies conducted from 1985 to 1987, preemergence applications of atrazine with cyanazine or simazine provided poor (≤60%) season-long control of this annual grass in no-tillage corn. Best season-long preemergence control was obtained with metolachlor or microencapsulated formulations of alachlor or EPTC. Postemergence applications of cyanazine or tridiphane + atrazine + crop oil provided poor giant foxtail control. Postdirected applications of paraquat resulted in fair (≥70%) control of giant foxtail through midseason. In greenhouse studies, triazineresistant (R) giant foxtail tolerated preemergence applications of atrazine or simazine at dosages to 9.0 kg ai/ha. Triazine-sensitive (S) giant foxtail was injured by 2.2 kg/ha and higher rates of atrazine and simazine. In laboratory studies, the I50for inhibition by atrazine of photoinduced electron transport in thylakoids isolated from S and R biotypes was determined to be 0.24 and 205 μM, respectively. The differential sensitivity was paralleled by simazine. However, the limited solubility of simazine prevented determination of an I50value with thylakoids from the R biotype.
Incorporation Depths of Imazaquin, Metribuzin, and Chlorimuron for Common Cocklebur (Xanthium strumarium) Control in Soybeans (Glycine max)
Authors: Wesley Richard A. , Shaw David R. , Barrentine William L.
Published: May 2019

Field experiments were conducted in 1986 and 1987 to evaluate the effect of herbicide incorporation to various depths on common cocklebur control with imazaquin, a tank mix of imazaquin and metribuzin, and a preformulated mixture of chlorimuron and metribuzin in soybeans. Herbicide rates included were two-thirds and the full registered rate. All treatments, except chlorimuron plus metribuzin (50 plus 320 g ai/ha, respectively), controlled more common cocklebur when incorporated to depths of 2.5 to 7.6 cm than when left unincorporated. Also, imazaquin at 90 g ai/ha and the tank mix of imazaquin plus metribuzin at 90 plus 280 g ai/ha, when incorporated, controlled more common cocklebur than higher rates of the same combination when not incorporated. Common cocklebur control was similar with 2.5-, 5.0-, and 7.6-cm soil incorporation depths.
The Effect of Sethoxydim on Corn (Zea mays) and Giant Foxtail (Setaria faberi)
Authors: Chernicky Jon P. , Gast Roger , Slife Fred W.
Published: May 2019

Corn and giant foxtail response to foliar-applied sethoxydim at 67, 134, and 200 g ai/ha was evaluated in field studies. Sethoxydim applied over the top of corn (60 cm tall) caused greater whorl damage and reduced corn grain yield more than postdirected sethoxydim. Sethoxydim controlled giant foxtail best when used in conjunction with a preemergence application of metolachlor (2.2 kg/ha) and atrazine (1.7 kg/ha).
Mathematical Description of Trifluralin Degradation in Soil
Authors: Reyes Carlos C. , Zimdahl Robert L.
Published: May 2019

Degradation of trifluralin in four soils, each represented at four sites, under field conditions was determined quantitatively and described mathematically. A biexponential equation that resulted from integration of first-order and second-order differential rate equations described degradation data better than the first-order kinetic model for 15 of 25 soil-site combinations. Biexponential model regression coefficients indicated extent of degradation and that degradation is rapid at initially high trifluralin concentrations but slows as concentration decreases. The first-order kinetic model initially underestimated but ultimately overestimated degradation of trifluralin, thereby inferring that a first-order half-life is inadequate for predicting trifluralin persistence.
Dicamba, Chlorsulfuron, and Clopyralid as Sprayer Contaminants on Sunflower (Helianthus annuus), Mustard (Brassica juncea), and Lentil (Lens culinaris), Respectively
Authors: Derksen Douglas A.
Published: May 2019

Simulated sprayer tank residues of the broadleaf weed herbicides dicamba, chlorsulfuron, and clopyralid applied alone and with the grass weed herbicides sethoxydim and diclofop on sunflower, tame mustard, and lentil, respectively, caused visible crop injury and reduced dry weight and yield. Dry weight production in the greenhouse and crop tolerance ratings in the field indicated that the grass weed herbicides enhanced crop injury from dicamba, chlorsulfuron, and clopyralid. Yield reductions in field experiments were also greater when dicamba and clopyralid were mixed with grass weed herbicides and applied on sunflower and lentil, respectively. This did not occur with chlorsulfuron applied to mustard. When mixed with simulated broadleaf weed herbicide residues, diclofop enhanced dry weight reductions and crop injury and reduced yield to a greater extent than sethoxydim. Crop tolerance ratings differentiated treatments and rates but were not a good estimate of the extent of yield loss. When broadleaf weed herbicides were applied at rates simulating sprayer tank residues alone or combined with grass weed herbicides, yield losses ranged up to 40% in sunflower, 70% in mustard, and 95% in lentil, compared to the untreated check.
Uptake and Action of Metribuzin in Soybeans (Glycine max) and Two Weed Species as Monitored by Chlorophyll Fluorescence
Authors: Ahrens William H.
Published: May 2019

Terminal fluorescence (FT) was monitored following root or foliar uptake of metribuzin in soybean, velvetleaf, and smooth pigweed seedlings grown in solution culture. These species are known to be tolerant, moderately susceptible, and susceptible, respectively, to metribuzin under field conditions. The indirect monitoring of herbicide metabolism by fluorescence is complicated by several factors (particularly photoinhibition) and is difficult to interpret when plants are kept in the light. Rapid declines in FTat metribuzin concentrations causing high photosystem II reaction center inhibition were interpreted, in conjunction with fresh weight and injury data, as resulting from photoinhibition in velvetleaf and smooth pigweed, and from a combination of photoinhibition and herbicide metabolism in soybeans. At lower concentrations, FTdeclines were apparently not affected by photoinhibition but were probably representative of herbicide metabolism. These results suggested a significant rate of metribuzin metabolism in soybeans, a minor degree of metabolism in smooth pigweed beginning after 12 h, and no detectable metabolism in velvetleaf. FTmonitored over a 24-h dark period following foliar absorption showed declines in soybeans indicating a modest degree of metribuzin metabolism (at intermediate herbicide doses) but no FTdeclines attributable to herbicide metabolism in velvetleaf or smooth pigweed. Results indicate that the inhibition of a high percentage of photosystem II reaction centers is required before photoinhibition and photooxidative leaf damage can result from photosystem II inhibitor herbicides such as metribuzin.
Effect of Bentazon, Imazaquin, and Chlorimuron on the Absorption and Translocation of the Methyl Ester of Haloxyfop
Authors: Croon Kent A. , Ketchersid Mary L. , Merkle Morris G.
Published: May 2019

Absorption and translocation of the methyl ester of haloxyfop (haloxyfop-methyl) in sorghum were reduced by presence of bentazon in the treatment emulsion. After 6 h, 18% of applied haloxyfop-methyl was recovered from the leaf surface in the absence of bentazon, compared to 43% of that applied in combination with bentazon. An average of 18% of applied haloxyfop-methyl was recovered as haloxyfop + haloxyfop-methyl from leaf tissues outside the treated zone in the absence of bentazon, compared to 8% of that applied in combination with bentazon. Haloxyfop-methyl absorption was similar whether applied with or without formulations of imazaquin or chlorimuron. However, the addition of imazaquin or chlorimuron to treatment emulsions decreased the translocation of haloxyfop + haloxyfop-methyl as only 13 and 12%, respectively, of the total amount of haloxyfop-methyl applied was translocated out of the treated zone. Mixtures of all herbicides were chemically stable; formulations of bentazon, imazaquin, or chlorimuron did not alter the ester or free acid levels of haloxyfop in an aqueous mixture over an 8-h period.
Differential Tolerance of Corn Genotypes to DPX-M6316
Authors: Eberlein Charlotte V. , Rosow Kathleen M. , Geadelmann Jon L. , Openshaw Stephen J.
Published: May 2019

Ten corn inbred lines were field evaluated for their tolerance to DPX-M6316 at 32 and 64 g ai/ha. Inbreds ‘A619′, ‘A641′, and ‘ND246’ were highly susceptible to DPX-M6316; inbreds ‘A671′, ‘A632′, and ‘B73’ were highly tolerant; and inbreds ‘A654′, ‘CM105′, ‘W153R’, and ‘M017’ were intermediate in their response. The basis for differential tolerance was studied by comparing the susceptibility of acetolactate synthase (ALS) to inhibition by DPX-M6316 in tolerant A671 and susceptible A619, and by examining the absorption, translocation, and metabolism of DPX-M6316 in both genotypes. I50values for DPX-M6316 inhibition of ALS activity in extracts from etiolated shoots of A671 and A619 were similar, 15.6 and 17.4 nM, respectively. There was little difference in14C-DPX-M6316 absorption by the two inbreds, but twice as much of the absorbed14C was translocated out of the treated leaf of A619 (13%) compared to A671 (6%). Differences in translocation may have been due to much more rapid DPX-M6316 metabolism in A671 than in A619. Extracts from treated leaves of A671 had only 23% DPX-M6316 remaining 5.5 h after treatment (HAT) compared to 78% DPX-M6316 remaining in extracts from A619 leaves. Therefore, rate of metabolism was the major factor involved in the tolerance of A671 and the susceptibility of A619 to DPX-M6316.
Competition of Spurred Anoda (Anoda cristata) and Velvetleaf (Abutilon theophrasti) with Cotton (Gossypium hirsutum) During Simulated Drought and Recovery
Authors: Patterson David T. , Highsmith Maxine T.
Published: May 2019

Cotton was grown alone (one plant/pot), in intraspecific competition (two plants/pot), and in interspecific competition with spurred anoda and velvetleaf in controlled-environment chambers, subjected to water stress by withholding water, and allowed to recover before the final harvest. Minimum leaf water potential reached during the drought period ranged from −1.87 MPa in cotton grown alone to −2.63 MPa in velvetleaf grown in intraspecific competition. Water stress reduced plant height, total dry weight, and leaf area in all species, compared to well-watered controls. Reductions in cotton growth due to intra- or interspecific competition were evident by 11 days following the onset of competition. The competitive impact of both weeds tended to increase with time. Growth reductions in cotton due to competition were associated primarily with reductions in leaf area duration; during drought the net assimilation rate also was reduced. Relative yields of cotton confirmed that interspecific competition from the weeds was more severe than intraspecific competition. Imposed drought did not affect the relative competitive abilities of the three species or the impact of the weeds on cotton.
Intraspecific and Interspecific Sicklepod (Cassia obtusifolia) Interference
Authors: Bozsa Robert C. , Oliver Lawrence R. , Driver Tony L.
Published: May 2019

Intraspecific interference of sicklepod and interspecific interference between sicklepod and soybeans were investigated in field experiments in 1982 and 1983. Sicklepod growth and reproductive parameters were reduced as intraspecific spacing between plants decreased from 90 to 2.5 cm. Sicklepod plants growing intraspecifically were competing at spacings below 90 cm. Soybean plant heights were affected only slightly by sicklepod interference. Soybeans grew little in height from 35 to 84 days after emergence, while sicklepod plants continued to grow until they were 30 to 45 cm taller than the soybeans. Sicklepod plants spaced 10 and 30 cm apart in soybeans reduced soybean yield (25 to 35%) more than sicklepod spaced 90 cm apart. Sicklepod produced 900 to 2000 seeds per plant even when growth was restricted by interference from soybeans.
Allelopathic Potential of Legume Debris and Aqueous Extracts
Authors: White Randall H. , Worsham A. Douglas , Blum Udo
Published: May 2019

Cotton and pitted morningglory emergence and dry weight decreased approximately 60 to 80% when these plants were grown under greenhouse conditions in the presence of increasing amounts (0.8 to 6.7 mg debris/g soil) of field-grown crimson clover or hairy vetch debris incorporated into the soil medium. Conversely, corn dry weight increased 20 to 75% when legume debris was placed on the soil surface; incorporated debris had very little effect on corn emergence or dry weight. Germination and seedling growth of corn, Italian ryegrass, cotton, pitted morningglory, and wild mustard decreased progressively, with species-dependent variation, when exposed to increasing concentrations (8.3 to 33.3 g debris/L) of aqueous crimson clover and hairy vetch extract. Mustard and ryegrass germination and growth were almost completely inhibited by full-strength extracts of both legumes. Bioassay species exhibited greater phytotoxic responses to hairy vetch than to crimson clover in the debris and extract studies. Emergence and growth of corn and cotton were not affected when planted into soil samples, containing root biomass and possible leaf and root exudates, collected from beneath field-grown hairy vetch and crimson clover plants. However, morningglory dry weight increased 35% in the presence of either legume root debris and accompanying soil.
Apical Dominance in Rhizomes of Quackgrass (Elytrigia repens): Inhibitory Effect of Scale Leaves
Authors: Robertson J. Mason , Taylor John S. , Harker K. Neil , Pocock Robert N. , Yeung Edward C.
Published: May 2019

Surgical experiments were conducted on cultured five-node apical rhizome segments of quackgrass. Removal of scale leaves promoted an initial burst of growth within the axillary buds but did not support the continued growth of buds as effectively as removal of the rhizome apex. Replacement of detached scale leaves over denuded buds temporarily repressed the promotive effect of scale leaf removal. Aqueous extracts of scale leaf material inhibited apical growth in rhizome segments but did not inhibit bud growth. Anatomical sections revealed that removal of scale leaves promoted development of buds: cells enlarged, vascular tissues differentiated, and new nodes began to form within 4 days of the removal of scale leaves. It is suggested that scale leaves contribute to apical dominance by inhibiting the initial development of axillary buds.
Interference of Hogpotato (Hoffmanseggia glauca) with Cotton (Gossypium hirsutum)
Authors: Castner Eric P. , Murray Don S. , Hackett Neil M. , Verhalen Laval M. , Weeks David L. , Stone John F.
Published: May 2019

The effects of hogpotato interference on cotton and of the crop on the weed were measured under field conditions in four environments. Full-season interference from 105 ± 21 hogpotato plants/m2reduced cotton plant height by 14 to 44%. Conversely, weed dry weight was reduced 54% through full-season interference from cotton. Lint yield reductions in cotton ranged from 31 to 98% following full-season weed interference. Interference during the first 7 weeks of crop growth reduced lint yield by approximately 40%; however, interference after 7 weeks of weed-free maintenance did not affect lint yield. Interference reduced boll size in 3 of 4 yr, lint percent in 2 of 4, and boll number in the only year it was measured. Cotton fiber length, uniformity index, and micronaire were reduced by full-season interference in 1 of 2 yr; however, fiber strength was not affected in either year. Significant use of soil water by hogpotato occurred at 120 cm and deeper in the soil while cotton used water primarily in the upper 75 cm.
Control of Horse Purslane (Trianthema portulacastrum) and Barnyardgrass (Echinochloa crus-galli) in Mung Bean (Vigna radiata)
Authors: Balyan Rajender S. , Malik Ram K.
Published: May 2019

Four postemergence herbicides were evaluated for control of horse purslane and barnyardgrass occurring alone and in combination in three separate field experiments at Haryana Agricultural University, Hisar (India). Haloxyfop, fluazifop, and sethoxydim controlled barnyardgrass. Fomesafen controlled horse purslane most effectively when applied at the two-branch stage of horse purslane in mung bean. Combinations of haloxyfop, fluazifop, or sethoxydim with fomesafen applied at the five-branch stage of horse purslane and two-leaf stage of barnyardgrass controlled both weeds. Mung bean treated with fomesafen at 250 g ae/ha plus haloxyfop at 190 or 250 g ae/ha, fluazifop at 750 or 1000 g ae/ha, or sethoxydim at 750 g or 1000 g ae/ha produced dry weights, pods/plant, and grain yield similar to weed-free mung bean.
Antagonism of Glyphosate Toxicity to Johnsongrass (Sorghum halepense) by 2,4-D and Dicamba
Authors: Flint Jerry L. , Barrett Michael
Published: May 2019

Greenhouse studies were conducted to determine the basis for reduced johnsongrass control when glyphosate was applied in mixtures with 2,4-D or dicamba. Glyphosate was applied to johnsongrass at 0.28, 0.56, 0.84, and 1.12 kg/ha alone and in combination with 2,4-D or dicamba at 0.14, 0.28, 0.14, or 0.56 kg/ha. Johnsongrass shoot and root fresh weights measured 4 weeks after treatment were higher when glyphosate was applied with 2,4-D (0.28 kg/ha glyphosate) or dicamba (0.28 kg/ha or 0.56 kg/ha glyphosate) compared to glyphosate applied alone at these rates. The antagonism of johnsongrass control was not observed with combinations of some of the higher glyphosate rates with 2,4-D (0.56 or 0.84 kg/ha glyphosate) or dicamba (0.84 or 1.12 kg/ha glyphosate). The reduction of glyphosate activity on johnsongrass occurred when any of four forms of 2,4-D or two forms of dicamba were added to the glyphosate spray mixture. Glyphosate uptake into johnsongrass leaves and subsequent translocation to the roots was reduced by the presence of 2,4-D or dicamba. The reduced glyphosate uptake and translocation could account for the decreased toxicity of glyphosate to johnsongrass when applied with 2,4-D or dicamba.