bluuebunny/crossref_metadata_2025 huggingface dataset:
Factors affecting eastern black nightshade (Solanum ptycanthum) seed germination
Authors: Zhou Jingkai , Deckard Edward L. , Messersmith Calvin G.
Published: July 2006

Effects of environmental factors, especially light, on eastern black nightshade seed germination were studied under growth chamber conditions. Germination occurred only when temperatures were 20 C or higher for 12 to 24 h d−1. Optimum germination occurred within the constant temperature range of 28 to 33 C or with alternating temperatures of 30/25 and 35/30 C. In the dark, eastern black nightshade germination was poor except at high alternating temperatures of 30/25 and 35/30 C. Seed germination was enhanced by light when temperatures were suboptimal. Imbibition was a prerequisite for response of eastern black nightshade seed to light. The light requirement for eastern black nightshade germination was partially overcome by cold stratification, gibberellic acid (GA3), and high or alternating temperatures. Germination of eastern black nightshade seed was promoted by short exposure to sunlight but was inhibited by prolonged exposure, especially when irradiance was high.
Inheritance of glyphosate resistance in rigid ryegrass (Lolium rigidum) from California
Authors: Simarmata Marulak , Bughrara Suleiman , Penner Donald
Published: July 2006

Glyphosate resistance was found in a rigid ryegrass population in northern California. A sample of the resistant plants were collected and grown under greenhouse conditions. The objective of this study was to evaluate glyphosate resistance in the progeny of the collected plants by recurrent selection, obtain the homozygous resistant and sensitive lines to establish dose-response curves, and to determine the inheritance of glyphosate resistance in rigid ryegrass. Diverse levels of resistance were observed in the first generation with survival of 89, 59, 45, and 9% from glyphosate at 1x, 2x, 4x, and 8x respectively, where x = 1.12 kg ha−1isopropylamine salt of glyphosate. Clones of plants that died from 1x were allowed to produce seed and were further subjected to recurrent selection to generate the most sensitive plants (S lines), which died from 0.125x glyphosate. The most resistant plants (R lines) were generated from the survivors receiving 8x glyphosate. The ratio between I50rates for the glyphosate resistant and the glyphosate sensitive plants was > 100-fold. The R and S lines were crossed reciprocally and F1progeny of both (R × S) and (S × R) showed intermediate resistance. These survived up to 2x glyphosate. The F2progeny were generated by intercrossing of F1plants. The ratio of sensitive, intermediate, and resistant plants in the F2population before the treatment of glyphosate at 0.125x followed by 8x was 1 : 16, 14 : 16, and 1 : 16 respectively, which corresponded to the Mendelian segregation ratio of two genes. The results indicated that the inheritance of glyphosate resistance in rigid ryegrass from California appeared to be nuclear, incompletely dominant, multigenic, and pollen-transmitted with no indication of maternal inheritance.
A model for predicting invasive weed and grass dynamics. II. Accuracy evaluation
Authors: Rinella Matthew J. , Sheley Roger L.
Published: July 2006

The impact of invasive weed management on plant community composition is highly dependent on location-specific factors. Therefore, treatment means from experiments conducted at a given set of locations will not reliably predict community response to weed management elsewhere. We developed a model that rescales treatment means to better match local conditions. The goal of this paper was to determine if this rescaling improves predictions. We used our model to predict leafy spurge stem length density and grass biomass data from field experiments. The experiments consisted of herbicide-treated plots, untreated controls, and, in some cases, grass seeding treatments. When herbicides suppressed leafy spurge, the model explained 21 to 48% more variation in grass response than did mean grass response to the same or similar herbicide treatments applied at other sites. When herbicides killed grass, the model explained 53% more variation in leafy spurge response than did mean leafy spurge response to the same herbicide treatment applied at other sites. We regressed model predictions against observed data and tested the null hypothesis that resulting slope terms were equal to 1.0. Because the null hypothesis was rejected in two of four tests, the model may systematically over- or underpredict in some situations. However, measurement error in the observed data, unintended herbicide injury, or an inaccurate allometric relationship may account for a major proportion of the systematic deviations, and these factors would not cause prediction error in some management applications. Because the model tends to be better than the means from experiments at predicting plant community composition, we conclude that the model could advance managers' ability to predict plant community responses to invasive weed management.
Association of the W574L ALS substitution with resistance to cloransulam and imazamox in common ragweed (Ambrosia artemisiifolia)
Authors: Zheng Danman , Patzoldt William L. , Tranel Patrick J.
Published: July 2006

Previous research revealed that resistance to cloransulam in at least one population of common ragweed was conferred by an altered herbicide target site, specifically, by a tryptophan-to-leucine amino acid substitution at position 574 (W574L) of acetolactate synthase (ALS). In this study, 22 common ragweed populations, several of which were suspected cloransulam resistant, were assayed to determine if the W574L ALS substitution was correlated with resistance to ALS inhibitors. From each population, 16 greenhouse-grown plants were treated with cloransulam, and another 16 were treated with imazamox. Plant dry weights were recorded 20 d after treatment and individual plants were considered resistant if their dry weight exceeded 50% of that of nonherbicide-treated controls. For each herbicide-treated plant, allele-specific primers were used in polymerase chain reactions to determine whether the ALS alleles contained leucine or tryptophan codons at position 574. Of the 352 plants treated with cloransulam, 70 were determined to be resistant, and all but two contained one or more Leu574alleles. The frequency of imazamox resistance was much higher than that of cloransulam in the populations, with 149 of 352 plants identified as imazamox resistant. However, only about half (80) of the imazamox-resistant plants contained one or more Leu574alleles. Correlation of imazamox resistance and Leu574alleles was population dependent. ALS activity assays confirmed that imazamox resistance in plants from at least one population was due to an altered target site, even though plants from that population did not have a W574L substitution. These results lead to the conclusion that a Leu574allele is the predominant basis for cloransulam resistance in common ragweed; however, other mechanisms of resistance to ALS inhibitors exist in some populations.
Effect of environmental factors on shoot emergence and vegetative growth of alligatorweed (Alternanthera philoxcroides)
Authors: Shen Jianying , Shen Mingquan , Wang Xiuhong , Lu Yitong
Published: July 2006

Laboratory and greenhouse studies were conducted to determine the effect of temperature, soil moisture, light, planting depth, and rhizome water content on shoot emergence and vegetative growth of alligatorweed. Optimum shoot emergence and growth occurred at constant 30 C, and no shoot emergence was found below constant 5 C. A maximum shoot emergence of 93% occurred at constant soil moisture of 30% with temperatures of 10 to 35 C. Shoot emergence and growth decreased as rhizome water content decreased, and shoot emergence did not occur below a rhizome water content of 20%. Shoot emergence and growth decreased with burial depth; shoot emergence was above 90% when rhizomes were buried 0.5 to 1.0 cm deep compared to 16% when they were buried 18 cm deep. Alligatorweed shoot emergence and vegetative growth were not significantly affected by light. In the fields, shoot emergence began in late March and culminated in May and June. These data help explain why this species is most commonly found in crop fields, orchards, roadsides, rivers, lakes, ponds, and irrigation canals. This information may aid in the development of more effective management measures, such as bringing alligatorweed rhizomes to the surface or below 20 cm deep to restrain its emergence and growth at winter or summer plowing.
Weed resistance to acetyl coenzyme A carboxylase inhibitors: an update
Authors: Délye Christophe
Published: July 2006

Herbicides targeting grass plastidic acetyl coenzyme A carboxylase (ACC) are effective selective graminicides. Their intensive use worldwide has selected for resistance genes in a number of grass weed species. Biochemistry and molecular biology have been the means of determining the herbicidal activity and selectivity toward crop plants of ACC-inhibiting herbicides. In recent years, elucidation of the tridimensional structure of ACC and identification of five amino acid residues within the ACC carboxyl transferase domain that are critical determinants for herbicide sensitivity shed light on the basis of ACC-based resistance to herbicides. However, metabolism-based resistance to ACC-inhibiting herbicides is much less well known, although this type of resistance seems to be widespread. A number of genes thus endow resistance to ACC-inhibiting herbicides, with the possibility for various resistance genes that confer dominant resistance at the herbicide field rate to accumulate within a single weed population or plant. This, together with a poor knowledge of the genetic parameters driving resistance, renders the evolution of resistance to ACC-inhibiting herbicides unpredictable. Future research should consider developing tactics to slow the spread of resistance. For this purpose, it is crucial that our understanding of metabolism-based resistance improves rapidly because this mechanism is complex and can confer resistance to herbicides with different target sites.
Fitness of double vs. single herbicide–resistant canola
Authors: Simard Marie-Josée , Légère Anne , Séguin-Swartz Ginette , Nair Harikumar , Warwick Suzanne
Published: July 2006

Since 1995, canola cultivars with herbicide resistance (HR) have been readily adopted by Canadian producers. Gene flow between these cultivars with different HR traits has led to the occurrence of double herbicide–resistant (2HR) volunteers. To evaluate the fitness of canola volunteers with double HR, we compared three 2HR combinations to each of their parent single-HR plants (1HR: glufosinate-R, imidazolinone-R, glyphosate-R) commercial canola lines in separate greenhouse experiments. The replacement series design included five ratios of 2HR vs. 1HR plants at a single density of 129 plants m−2and three stress treatments: herbicide application with either glufosinate, imazethapyr, or glyphosate; competition with a wheat crop; and a control without herbicide or wheat competition. Fitness indicators included aboveground biomass at 5 and 12 to 16 wk, seed production, and reproductive allocation. The 2HR plants showed delayed reproductive growth but were generally as competitive as 1HR commercial lines. Plant biomass of 2HR canola was comparable to or greater than 1HR canola, whereas seed biomass of 2HR canola was less than that of 1HR canola in half of the cases, likely because of delayed reproductive growth and early harvesting. Glufosinate–glyphosate 2HR was the fittest combination. Herbicide application had little effect on 2HR biomass at harvest, except for imazethapyr, which reduced the biomass and seed production of 2HR plants with imidazolinone-glyphosate resistance by 30%. The latter effect could have been from the unsuspected presence of 2HR plants with only one of the two acetolactate synthase mutations conferring resistance to imidazolinones. Wheat competition reduced fitness values of both 2HR and 1HR canola similarly, but seed production was still 64% that of the controls. Overall, there was little indication of reduced fitness in 2HR canola compared with commercial 1HR varieties.
Herbicidal activity of eight isothiocyanates on Texas panicum (Panicum texanum), large crabgrass (Digitaria sanguinalis), and sicklepod (Senna obtusifolia)
Authors: Norsworthy Jason K. , Meehan John T.
Published: July 2006

A greenhouse experiment was conducted to evaluate the herbicidal activity of five aliphatic (ethyl, propyl, butyl, allyl, and 3-methylthiopropyl) and three aromatic (phenyl, benzyl, 2-phenylethyl) isothiocyanates on Texas panicum, large crabgrass, and sicklepod. All isothiocyanates were applied to soil at 0, 10, 100, 1,000, and 10,000 nmol g−1of soil and incorporated. Weed emergence was generally stimulated at the lower isothiocyanate concentrations, but all isothiocyanates provided 37% or more suppression of each species at the highest concentration. Propyl and allyl isothiocyanate were most effective in suppressing Texas panicum, with 50% effective dose (ED50) values of 345 and 409 nmol g−1of soil. All aliphatic isothiocyanates reduced Texas panicum density by at least 98%. Allyl and 3-methylthiopropyl isothiocyanate were the most effective aliphatics on large crabgrass, with density reductions of 98 and 100%, respectively. All aromatic isothiocyanates reduced large crabgrass density by 86 to 96%. Sicklepod was generally the most tolerant of the three species evaluated, with ED50values for ethyl, propyl, and butyl isothiocyanate being greater than the evaluated concentrations. Maximum reduction in sicklepod density was 72, 68, 65, and 62%, which was achieved with allyl, benzyl, 3-methylthiopropyl, and phenyl isothiocyanate, respectively. This research shows that soil-applied and incorporated isothiocyanates are effective in suppressing some important weeds of the southeastern United States, but effectiveness of each isothiocyanate varies among species. Application techniques that minimize loss of volatile isothiocyanates may further improve their potential as an effective means of controlling these and other troublesome weeds.
Combining agronomic practices and herbicides improves weed management in wheat–canola rotations within zero-tillage production systems
Authors: Blackshaw Robert E. , Beckie Hugh J. , Molnar Louis J. , Entz Toby , Moyer James R.
Published: July 2006

Development of more comprehensive and cost-effective integrated weed management systems is required to facilitate greater integrated weed management adoption by farmers. A field experiment was conducted at two locations to determine the combined effects of seed date (April or May), seed rate (recommended or 150% of recommended), fertilizer timing (applied in fall or spring), and in-crop herbicide dose (50% or 100% of recommended) on weed growth and crop yield. This factorial set of treatments was applied in four consecutive years within a spring wheat–spring canola–spring wheat–spring canola rotation in a zero-till production system. Both wheat and canola phases of the rotation were grown each year. Weed biomass was often lower with May than with April seeding because more weeds were controlled with preplant glyphosate. However, despite fewer weeds being present with May seeding, wheat yield was only greater in 1 of 7 site-years, and canola yield was never greater with May compared with April seeding. Higher crop seed rates had a consistently positive effect on reducing weed growth and the weed seedbank. Crop yield was sometimes greater, and never lower, with higher seed rates. Fertilizer timing did not have a large effect on crop yield, but applying N in the spring compared with fall was less favorable for weeds as indicated by lower weed biomass and a 20% decrease in the weed seedbank. In-crop herbicides applied at 50% compared with 100% doses often resulted in similar weed biomass and crop yield, especially when higher crop seed rates were used. Indeed, the weed seedbank at the conclusion of the 4-yr experiment was not greater with the 50% compared with 100% herbicide dose at one of two locations. This study demonstrates the combined merits of early seeding (April), higher crop seed rates, and spring-applied fertilizer in conjunction with timely but limited herbicide use to manage weeds and maintain high crop yields in rotations containing wheat and canola.
Synergism between cover crop residue and herbicide activity on emergence and early growth of weeds
Authors: Teasdale John R. , Pillai Parthan , Collins Ronald T.
Published: July 2006

Cover crop residues and other biologically based approaches often provide incomplete and inconsistent weed control. This research was conducted to evaluate interactions between hairy vetch residue on the surface of soil and the herbicide metolachlor. Herbicide was applied and incorporated with simulated rainfall before residue placement, residue was applied to the soil surface at precise rates, and potentially confounding variables such as nitrogen and soil moisture were controlled in a greenhouse experiment. Emphasis was placed on the use of suboptimal rates of both residue and metolachlor to explore the potential synergistic interactions between these factors. Deviation from a multiplicative model that included a quadratic response to hairy vetch residue and a log-logistic response to metolachlor was used to demonstrate the presence or absence of synergism. This model effectively showed that emergence of smooth pigweed, common lambsquarters, giant foxtail, and velvetleaf and early growth of smooth pigweed and common lambsquarters were reduced synergistically by the combination of hairy vetch residue and metolachlor. For example, smooth pigweed emergence was reduced 13% by 500 g m−2of hairy vetch residue alone and was reduced 16% by 10 g ha−1of metolachlor alone, but together, they reduced smooth pigweed emergence by 86%. This model could be used to determine synergistic interactions between any combination of a phytotoxin and a biologically based weed management approach that could be expressed in quantitative units.
Nitrogen supply affects root:shoot ratio in corn and velvetleaf (Abutilon theophrasti)
Authors: Bonifas Kimberly D. , Walters Daniel T. , Cassman Kenneth G. , Lindquist John L.
Published: July 2006

Competitive outcome between crops and weeds is affected by partitioning of new biomass to above- and belowground plant organs in response to nutrient supply. This study determined the fraction of biomass partitioned to roots vs. shoots in corn and velvetleaf in response to nitrogen (N) supply. Pots measuring 28 cm in diam and 60 cm deep were embedded in the ground and each contained one plant of either corn or velvetleaf. Each plant received one of three N treatments: 0, 1, or 3 g N applied as ammonium nitrate in 2001, and 0, 2, or 6 g N in 2002. Measurements of total above- and belowground biomass were made at 10 sampling dates during each growing season. The root:shoot ratio decreased over time for both corn and velvetleaf as a result of normal plant growth and as N supply increased. Root:shoot ratio was greater for corn than for velvetleaf at comparable stages of development and at all levels of N supply. Both corn and velvetleaf display true plasticity in biomass partitioning patterns in response to N supply. Velvetleaf root:shoot ratio increased by 46 to 82% when N was limiting in 2001 and 2002, respectively, whereas corn root:shoot ratio increased by only 29 to 45%. The greater increase in biomass partitioned to roots by velvetleaf might negatively impact its ability to compete with corn for light when N supply is limited.
Assessment of two nondestructive assays for detecting glyphosate resistance in horseweed (Conyza canadensis)
Authors: Koger Clifford H. , Shaner Dale L. , Henry W. Brien , Nadler-Hassar Talia , Thomas Walter E. , Wilcut John W.
Published: July 2006

Two rapid, nondestructive assays were developed and tested for their potential in differentiating glyphosate-resistant from glyphosate-susceptible biotypes of horseweed. In one assay, leaves of glyphosate-resistant and -susceptible corn, cotton, and soybean plants, as well as glyphosate-resistant and -susceptible horseweed plants, were dipped in solutions of 0, 300, 600, and 1,200 mg ae L−1glyphosate for 3 d, and subsequent injury was evaluated. In the second assay, plant sensitivity to glyphosate was evaluated in vivo by incubating excised leaf disc tissue from the same plants used in the first assay in 0.7, 1.3, 2.6, 5.3, 10.6, 21.1, 42.3, and 84.5 mg ae L−1glyphosate solutions for 16 h and measuring shikimate levels with a spectrophotometer. The leaf dip assay differentiated between glyphosate-resistant and -susceptible crops and horseweed biotypes. The 600 mg L−1rate of glyphosate was more consistent in differentiating resistant and susceptible plants compared with the 300 and 1,200 mg L−1rates. The in vivo assay detected significant differences between susceptible and glyphosate-resistant plants of all species. Shikimate accumulated in a glyphosate dose–dependent manner in leaf discs from susceptible crops, but shikimate did not accumulate in leaf discs from resistant crops, and levels were similar to nontreated leaf discs. Shikimate accumulated at high (≥ 21.1 mg ae L−1) concentrations of glyphosate in leaf discs from all horseweed biotypes. Shikimate accumulated at low glyphosate concentrations (≤ 10.6 mg L−1) in leaf discs from susceptible horseweed biotypes but not in resistant biotypes. Both assays were able to differentiate resistant from susceptible biotypes of horseweed and could have utility for screening other weed populations for resistance to glyphosate.
Assessment of two nondestructive assays for detecting glyphosate resistance in horseweed (Conyza canadensis)
Authors: Koger Clifford H. , Shaner Dale L. , Henry W. Brien , Nadler-Hassar Talia , Thomas Walter E. , Wilcut John W.
Published: July 2006

Two rapid, nondestructive assays were developed and tested for their potential in differentiating glyphosate-resistant from glyphosate-susceptible biotypes of horseweed. In one assay, leaves of glyphosate-resistant and -susceptible corn, cotton, and soybean plants as well as glyphosate-resistant and -susceptible horseweed plants were dipped in solutions of 0, 300, 600, and 1200 mg ae L−1glyphosate for 3 d and subsequent injury was evaluated. In the second assay, plant sensitivity to glyphosate was evaluated in vivo by incubating excised leaf disc tissue from the same plants used in the first assay in 0.7, 1.3, 2.6, 5.3, 10.6, 21.1, 42.3, and 84.5 mg ae L−1glyphosate solutions for 16 h and measuring shikimate levels with a spectrophotometer. The leaf-dip assay differentiated between glyphosate-resistant and -susceptible crops and horseweed biotypes. The 600 mg L−1rate of glyphosate was more consistent in differentiating resistant and susceptible plants compared with the 300 and 1,200 mg L−1rates. The in vivo assay detected significant differences between susceptible and glyphosate-resistant plants of all species. Shikimate accumulated in a glyphosate dose-dependent manner in leaf discs from susceptible crops, but shikimate did not accumulate in leaf discs from resistant crops and levels were similar to nontreated leaf discs. Shikimate accumulated at high (≥ 21.1 mg ae L−1) concentrations of glyphosate in leaf discs from all horseweed biotypes. Shikimate accumulated at low glyphosate concentrations (≤ 10.6 mg L−1) in leaf discs from susceptible horseweed biotypes but not in resistant biotypes. Both assays were able to differentiate resistant from susceptible biotypes of horseweed and might have utility for screening other weed populations for resistance to glyphosate.
Temperature effects on jointed goatgrass (Aegilops cylindrica) seed germination
Authors: Fandrich Lynn , Mallory-Smith Carol
Published: July 2006

A better understanding of the persistence of jointed goatgrass seed in soil and its dormancy will lead to the development of more effective weed-management strategies. Three populations of jointed goatgrass were collected from winter wheat fields in Oregon, and grown together with the winter wheat variety ‘Madsen’ in nurseries at Moro and Pendleton, OR. Germination responses of jointed goatgrass and wheat seed were recorded over 14 d at 5/5, 15/10, 15/15, 25/15, 25/25, and 30/20 C day/night temperatures and a 12-h photoperiod. Because jointed goatgrass spikelets often contain two seed, primary and secondary seed germination values were recorded. Secondary seed germination was defined as 3-mm radicle protrusion, and primary seed germination was defined as 5-mm emergence of the second coleoptile. Jointed goatgrass secondary seed germinated when exposed to all temperature regimes. Jointed goatgrass secondary seed germination occurred 3 d earlier in temperature regimes involving 15 C compared to germination at 5/5, 25/25, and 30/20 C. Final germination values for jointed goatgrass secondary seed were greatest when seed were incubated at 25/15 C. Wheat seed germinated at all temperature regimes, although the onset of germination occurred 1 to 1.5 d later at 5/5 C compared to other temperature regimes. Jointed goatgrass primary seed germinated only at 15/10, 15/15, and 25/15 C, and maximum germination occurred at 25/15 C. Dormancy in jointed goatgrass might prevent germination of seed within freshly shattered spikelets until autumn when temperatures are low and moisture is available. Because final germination percentages in jointed goatgrass primary and secondary seed were less than 100%, additional research on factors regulating dormancy is needed.
Impact of a terminated wheat cover crop in irrigated corn on atrazine rates and water use efficiency
Authors: Currie Randall S. , Klocke Norman L.
Published: July 2006

A study was conducted near Garden City, KS with irrigated corn to determine how the integration of a terminated winter wheat cover crop with various atrazine rates would affect Palmer amaranth control and corn water use efficiency (WUE). Without atrazine, the presence of a winter wheat cover crop, killed in the boot stage, resulted in a threefold weed biomass reduction in irrigated corn. The highest rate of atrazine completely masked the weed control effect of the cover crop, producing a greater than 15-fold reduction regardless of the presence or absence of the cover crop. A terminated winter wheat cover crop without atrazine elevated corn yield in only two of nine location-yr, and in one instance, depressed yield. However, a terminated wheat cover crop elevated corn yield in six of nine location-yr combinations when used in conjunction with 1.6 kg ha−1atrazine. Although increases in WUE associated with reductions in soil water evaporation produced by the cover crop seemed to be responsible for some of the increase in corn grain yield and stored soil water at the end of the summer growing season, end of season Palmer amaranth biomass had a more profound impact.
White Clover (Trifolium repens) Control and Flower Head Suppression in Apple Orchards
Authors: MacRae Andrew W. , Mitchem Wayne E. , Monks David W. , Parker Michael L.
Published: July 2006

White clover is a weed in apple orchards that competes with the crop; also, flowers of this weed are unwanted attractants of honey bees at times when insecticides, which are harmful to these pollinators, are being applied. In 1997 and 1998, white clover flower head and plant control by clopyralid alone and with 2,4-D and apple tolerance to these herbicides were determined. Treatments consisted of clopyralid at 0.10 and 0.21 kg ae/ha, 2,4-D at 1.1 kg ae/ha, and 2,4-D at 1.1 kg ae/ha plus 0.03 or 0.05 kg ae/ha clopyralid, which were applied 2 wk before full apple bloom and 2 wk after full apple bloom, and a nontreated check. No crop injury occurred with any treatment. All herbicide treatments provided some white clover control and flower head suppression. No differences in white clover bloom reduction were observed through May among treatments containing clopyralid. As summer progressed, the effect of clopyralid rate became more apparent. Clopyralid at 0.21, regardless of application time, provided 99% vegetative control and 100% flower head reduction through July. Clopyralid plus 2,4-D controlled white clover better than 2,4-D alone. However, vegetative control and flower head reduction with clopyralid at reduced rates (0.03 or 0.05 kg ae/ha) plus 2,4-D were not acceptable (76% or less and 78% or less, respectively). Thus, clopyralid at 0.10 and 0.21 kg ae/ha will be necessary for acceptable white clover vegetation control and flower head reduction.
Tropical Signalgrass (Urochloa subquadripara) Control with Preemergence- and Postemergence-Applied Herbicides
Authors: Teuton Travis C. , Unruh J. Bryan , Brecke Barry J. , Macdonald Greg E. , Miller Grady L. , Ducar Joyce Tredaway
Published: July 2006

Tropical signalgrass is one of the most serious weed problems in the St. Augustinegrass sod production in Florida, and its presence increases production costs and lowers turfgrass quality. The objectives of our research were to: (1) evaluate herbicides preemergence and postemergence for control of tropical signalgrass and (2) compare control of tropical signalgrass and other problem weeds (torpedograss, blanket crabgrass, and India crabgrass) with postemergence herbicides. In preemergence herbicide field trials, only benefin + oryzalin, imazapic, imazapic + 2,4-D, and oryzalin provided ≥75% tropical signalgrass control 8 wk after application (WAA). By 11 WAA, only benefin + oryzalin and imazapic + 2,4-D provided ≥75% tropical signalgrass control. In greenhouse experiments, eight herbicide treatments were applied postemergence to tropical signalgrass seedlings at the two-, four-, six-, and eight-leaf stages. Asulam and CGA 362622 provided ≥89% tropical signalgrass control at all application timings. Imazaquin controlled tropical signalgrass ≥98% when applied before the eight-leaf stage. However, in field trials with mature tropical signalgrass (>20 cm stolons), none of the 20 herbicide treatments applied postemergence provided acceptable control.
Evaluating the Potential for Site-Specific Herbicide Application in Soybean
Authors: Wilkerson Gail G. , Price Andrew J. , Bennett Andrew C. , Krueger David W. , Roberson Gary T. , Robinson Bridget L.
Published: July 2006

Field experiments were conducted on two North Carolina research stations in 1999, 2000, and 2001; on-farm in Lenoir, Wayne, and Wilson counties, NC, in 2002; and on-farm in Port Royal, VA, in 2000, 2001, and 2002 to evaluate possible gains from site-specific herbicide applications at these locations. Fields were scouted for weed populations using custom software on a handheld computer linked to a Global Positioning System. Scouts generated field-specific sampling grids and recorded weed density information for each grid cell. The decision aid HADSS™ (Herbicide Application Decision Support System) was used to estimate expected net return and yield loss remaining after treatment in each sample grid of every field under differing assumptions of weed size and soil moisture conditions, assuming the field was planted with either conventional or glyphosate-resistant (GR) soybean. The optimal whole-field treatment (that treatment with the highest expected net return summed across all grid cells within a field) resulted in average theoretical net returns of $79/ha (U.S. dollars) and $139/ha for conventional and GR soybean, respectively. When the most economical treatment for each grid cell was used in site-specific weed management, theoretical net returns increased by $13/ha (conventional) and $4.50/ha (GR), and expected yield loss after treatment was reduced by 10.5 and 4%, respectively, compared with the whole-field optimal treatment. When the most effective treatment for each grid cell was used in site-specific weed management, theoretical net returns decreased by $18/ha (conventional) and $4/ha (GR), and expected yield loss after treatment was reduced by 27 and 19%, respectively, compared with the whole-field optimal treatment. Site-specific herbicide applications could have reduced the volume of herbicides sprayed by as much as 70% in some situations but increased herbicide amounts in others. On average, the whole-field treatment was optimal in terms of net return for only 35% (conventional) and 57% (GR) of grid cells.
Evaluation of Three Winter Cereals for Weed Control in Conservation-Tillage Nontransgenic Cotton
Authors: Reeves D. Wayne , Price Andrew J. , Patterson Michael G.
Published: July 2006

The increased use of conservation tillage in cotton production requires that information be developed on the role of cover crops in weed control. Field experiments were conducted from fall 1994 through fall 1997 in Alabama to evaluate three winter cereal cover crops in a high-residue, conservation-tillage, nontransgenic cotton production system. Black oat, rye, and wheat were evaluated for their weed-suppressive characteristics compared to a winter fallow system. Three herbicide systems were used: no herbicide, preemergence (PRE) herbicides alone, and PRE plus postemergence (POST) herbicides. The PRE system consisted of pendimethalin at 1.12 kg ai/ha plus fluometuron at 1.7 kg ai/ha. The PRE plus POST system contained an additional application of fluometuron at 1.12 kg/ha plus DSMA at 1.7 kg ai/ha early POST directed (PDS) and lactofen at 0.2 kg ai/ha plus cyanazine at 0.84 kg ai/ha late PDS. No cover crop was effective in controlling weeds without a herbicide. However, when black oat or rye was used with PRE herbicides, weed control was similar to the PRE plus POST system. Rye and black oat provided more effective weed control than wheat in conservation-tillage cotton. The winter fallow, PRE plus POST input system yielded significantly less cotton in 2 of 3 yr compared to systems that included a winter cover crop. Use of black oat or rye cover crops has the potential to increase cotton productivity and reduce herbicide inputs for nontransgenic cotton grown in the Southeast.
Coastal Bermudagrass (Cynodon dactylon) Yield Response to Various Herbicides
Authors: Butler Twain J. , Muir James P.
Published: July 2006

Several new herbicides have been registered for pasture weed control, but their effect on ‘Coastal’ bermudagrass dry matter (DM) yield has not been documented. The objective of this study was to determine the effect of clopyralid, fluroxypyr, imazapic, picloram, picloram + fluroxypyr, picloram + 2,4-D amine, triasulfuron + dicamba, triclopyr amine + clopyralid, triclopyr ester, triclopyr ester + fluroxypyr, trifloxysulfuron, 2,4-D amine + dicamba, and 2,4-D ester on Coastal bermudagrass yield. Total DM yields of Coastal bermudagrass were not reduced by 0.84 kg/ha clopyralid, 0.031 kg ai/ha triasulfuron + 0.44 kg ai/ha dicamba, 1.205 kg ai/kg 2,4-D amine + 0.42 kg/ha dicamba, and 2.31 kg/ha 2,4-D ester. Although 0.227 kg ai/ha picloram + 0.84 kg/ha 2,4-D amine, 0.945 kg ai/ha triclopyr amine + 0.315 kg ai/ha clopyralid, and 1.68 kg ai/ha triclopyr ester reduced Coastal bermudagrass DM yields in harvest 1, there was no cumulative loss in total production in either 2001 or 2002 with these herbicides compared with that of the nontreated control. Coastal bermudagrass total DM yields were reduced by 52% with 0.158 kg ai/ha imazapic when applied to dormant bermudagrass in 2001, and by 26% with 0.021 kg ai/ha trifloxysulfuron when applied to actively growing bermudagrass in 2001; however, neither herbicide reduced total cumulative yield in 2002. In 2001 and 2002, total DM yield was reduced by an average of 25% with 0.42 kg/ha fluroxypyr, by 45% with 0.105 kg/ha imazapic, by 57% with 0.158 kg/ha imazapic, by 65% with 0.21 kg/ha imazapic, by 25% with 0.56 kg/ha picloram, by 20% with 0.188 kg/ha picloram + 0.188 kg/ha fluroxypyr, and by 18% with 0.63 kg/ha triclopyr ester + 0.21 kg/ha fluroxypyr, when applied to actively growing Coastal bermudagrass.
Efficacy and Tolerance of Flumioxazin on Sweetpotato (Ipomoea batatas)
Authors: Kelly Steven T. , Shankle Mark W. , Miller Donnie K.
Published: July 2006

Experiments were conducted at three locations in Louisiana in 2002 and 2003 to evaluate flumioxazin (36, 72, or 109 g ai/ha) applied pretransplant (PRE) or post-transplant (POST) to sweetpotato. All treatments were applied immediately before or after sweetpotato transplanting to weed-free beds. PRE applications caused 4% or less injury with any rate of flumioxazin at 9 or 18 d after transplanting (DATr) compared with 18 to 20% injury at 9 DATr and 6 to 14% at 18 DATr with 72 or 109 g/ha POST, respectively. Injury from PRE applications of flumioxazin were not different from injury with clomazone (840 g ai/ha) applied POST. Injury at Chase, LA, in 2002 was 8% and less with flumioxazin PRE, but 35 to 83% with flumioxazin POST and appeared to be due to the use of greenhouse-grown cuttings instead of field-grown cuttings, which were used in the other two experiments. There was no interaction between experiments for sweetpotato yield. Plots treated with flumioxazin PRE or 36 g/ha POST yielded greater than sweetpotato treated with clomazone for U.S. No. 1 and 2 grade yield as well as total marketable yield. No differences were observed in yellow nutsedge control with any rate of flumioxazin. At 34 or 50 DATr, flumioxazin controlled yellow nutsedge 73 to 85% with 72 or 109 g/ha applied PRE or POST. Flumioxazin, regardless of application timing or rate, controlled carpetweed and spiny amaranth at least 86%. A similar experiment in Mississippi evaluated tank-mixes of flumioxazin (36, 72, or 109 g/ha) and clomazone (840 g/ha) applied PRE or POST. No sweetpotato injury was observed with flumioxazin PRE. However, injury from flumioxazin POST increased with increased rates (18 to 50% at 18 DATr and 16 to 93% at 25 DATr). Weed control was greater than 80% with all treatments.
Evaluation of Flumioxazin and Other Herbicides for Weed Control in Gladiolus
Authors: Richardson Robert J. , Zandstra Bernard H.
Published: July 2006

Two studies were conducted near Bronson, MI, to determine gladiolus tolerance and weed control with flumioxazin and other herbicide treatments. The first study was conducted in 2002, 2003, and 2004 to evaluate weed control and gladiolus injury with flumioxazin and 14 other preemergence treatments. Crop injury over the 3-yr period was less than 6% and was considered commercially acceptable with flumioxazin, linuron, oryzalin, pendimethalin, prometryn, S-metolachlor, and sulfentrazone. Gladiolus stand count, height, and flower count were similar to those of the nontreated control with these treatments. Clomazone, halosulfuron, imazamox, imazapic, mesotrione, oxyfluorfen, rimsulfuron, and trifloxysulfuron resulted in unacceptable crop injury. Of the acceptable treatments, only flumioxazin controlled common ragweed, yellow nutsedge, and foxtail species at least 68%. The second study was conducted in 2003 and 2004. Flumioxazin was evaluated at four rates, in mixtures with S-metolachlor and oryzalin, and in comparison with isoxaben plus oryzalin. Gladiolus injury did not exceed 6%. Common ragweed, annual grass, and yellow nutsedge control were at least 63% with all flumioxazin treatments.
Absolute and relative measures for evaluating the forecasting performance of time series models for daily streamflows
Authors: Astatkie T.
Published: July 2006

Root Mean Squared Error (RMSE) and Mean Absolute Error (MAE) are widely used measures for evaluating the forecasting performance of time series models. Although these absolute measures can be used to compare the performance of competing models, one needs a reference to judge the goodness of the forecasts. In this paper, two relative measures, coefficient of efficiency (E) and index of agreement (d), and their modified versions (EM, EMP, dM and dMP) with desired values of closer to one are presented. These measures are illustrated by comparing the modeling ability and validation forecasting performance of a Nonlinear Additive Autoregressive with Exogenous variables (NAARX), Nested Threshold Autoregressive (NeTAR), and Multiple Nonlinear Inputs Transfer Function (MNITF) models developed for the Jökulsá eystri daily streamflow data. The results suggest that NeTAR describes the system best, and gives better 1- and 2-day ahead validation forecasts. MNITF gives better forecasts for 3-day ahead, and NeTAR and NAARX give comparable performance for 4- and 5-day ahead forecasting. The values of E and d were larger than those of the modified versions, giving a false sense of model performance, and unlike the modified versions, they decreased as forecast lead times increased. Differences among the values of these six relative measures can reveal the sensitiveness of competing models to outliers, and their potential for long-term forecasting. Accordingly, NeTAR was the least sensitive to outliers and NAARX was the most sensitive, with MNITF in between; and NAARX showed the most potential for long-term streamflow forecasting.
A robust stage-discharge rating curve model based on critical flow from a reservoir
Authors: Petersen-Øverleir Asgeir
Published: July 2006

Hydrometric gauging stations are often sited in reservoirs such as lakes and river pools since they possess favourable features for streamflow determination. By applying the equations which govern critical flow from a reservoir along with a spline representation of the known geometric characteristics of the reservoir outlet, a new method is developed for estimating the stage-discharge relationship in reservoir-like situations. The proposed rating curve model is amenable to least squares estimation using the available stage-discharge measurements. The proposed model is shown by theory to be general, and includes both normal uniform flow from a reservoir and the classical power-law rating curve model as special cases. Using geometric data and stage-discharge measurements from two Norwegian gauging stations, it is demonstrated that (a) the proposed model is more appropriate than the classical power-law rating curve model when performance is measured by the AIC statistic and the sizes of the jackknife standard deviations of the predicted discharges, and (b) the proposed model displays a superior performance over the power-law model in both upwards and downwards extrapolation.
Evapotranspiration estimation using feed-forward neural networks
Authors: Kişi Özgür
Published: July 2006

Two different feed-forward neural network algorithms, Levenberg–Marquardt (LM) and conjugate gradient (CG), are used for estimation of daily reference evapotranspiration (ET) from climatic data. The performances of the LM and CG algorithms in estimating ET are analyzed and discussed and various combinations of wind speed, solar radiation, relative humidity, air and soil temperature data as inputs to the artificial neural network (ANN) models are examined in the study so as to evaluate the degree of the effect of each of these variables on ET. The LM and CG training algorithms are compared with each other according to their convergence velocities in training and estimation performances of ET. The results of the ANN models are compared with those of multi-linear regression (MLR) and the empirical models of Penman and Hargreaves. Based on the comparisons, it was found that the neural computing technique could be employed successfully in modelling evapotranspiration process from the avaliable climatic data.
Transport of organic carbon from the Mogot Experimental Watershed in the southern mountainous taiga of eastern Siberia
Authors: Suzuki Kazuyoshi , Konohira Eiichi , Yamazaki Yusuke , Kubota Jumpei , Ohata Tetsuo , Vuglinsky Valery
Published: July 2006

More than 60% of river runoff from the Lena River basin originates in the southern mountainous region of eastern Siberia within the permafrost zone. We studied the transport of dissolved organic carbon (DOC) and particulate organic carbon (POC) within the Mogot Experimental Watershed, which is close to the drainage divide between the Lena and Amur River basins in the southern mountainous taiga region, from 1 August 2000 to 12 November 2001. DOC concentration was strongly related to thawing depth at the bottom of the main valley when thawing depth was less than 20 cm during snowmelt runoff. When thawing depth was equal to or greater than 20 cm, DOC concentration was more closely related to the rate of river discharge in summer runoff. On the basis of our observations, we extrapolated the annual transport of DOC and POC to be 4.75 g C m−2 yr−1 and 0.03 C kg C m−2 yr−1, respectively. Transport of organic carbon from the catchment was about 4.78 g C m−2 yr−1 during 2001. DOC is the main form of organic carbon flux in the study area.
Lévy-statistics for partially equilibrated systems
Authors: Petridis Athanasios
Published: July 2006

We examine deviations from Boltzmann-Gibbs statistics for a certain class of partially equilibrated systems of finite size. We find that such systems are characterized by the Lévy distribution whose non-extensivity parameter is related to the number of internally equilibrated subsystems and to correlations among them. This concept is applicable to relativistic heavy ion collisions.
A virtual instrumentation based protocol for the automated implementation of the inner field compensation method
Authors: Mereuta Loredana , Luchian Tudor
Published: July 2006

One influential parameter which mediates interactions between many types of molecules and biological membranes stems from the lumped contributions of the transmembrane potential, dipole potential and the difference in the surface potentials on both sides of a membrane. With relevance to cell physiology, such electrical features of a biomembrane are prone to undergoing changes as a result of interactions with the aqueous surrounding. Among the most useful tools devoted to exploring changes of electrical parameters of a lipid membrane induced by certain extracellular ions, lipid composition, and embedded membrane peptides and proteins, are spectroscopic imaging and the inner field compensation (IFC) method. In this work we layout the principles of a fully computerized version of the IFC method, which makes it more readily available to users. As a direct application, we deployed this improved version of the IFC method to time-resolve changes induced by alamethicin monomers upon membrane dipole potential, following their aggregation within an artificial lipid membrane. Intriguingly, even prior crossing the membrane core, the membrane-bound alamethicin monomers are shown to significantly increase the dipole potential of the monolayer they reside in. Such data further emphasize the yet less-explored interplay between membrane-based protein and peptides, and the membrane dipole potential.
Radial distribution of hydrogen atoms in H
2 plasma
Authors: Mijović Slavoljub , Vučeljić Mira
Published: July 2006

The radial intensities of the H
α and H
2 Fulcher α (d
3Πu − a
3Σg) system spectral lines were used to obtain the radial distribution of hydrogen atoms in H
2 plasma discharge. We have obtained new equations in order to describe the distribution of atoms in molecule discharges. Abel’s integral equation has been solved by Tikhonov’s regularization procedure. Model functions have been introduced to examine the limitations in the applicability of this method. An estimation of the degree of dissociation in the radial direction has been obtained.
Small damping approach in Fermi-liquid theory
Authors: Kolomietz Volodymyr , Lukyanov Sergiy , Shlomo Shalom
Published: July 2006

The validity of the small damping approximation (SDA) for the quasi-classical description of the averaged properties of nuclei at high temperatures is studied within the framework of collisional kinetic theory. The isoscalar collective quadrupole vibrations in hot nuclei are considered. We show that the extension of the SDA, by accounting for the damping of the distribution function δ f in the collision integral, reduces the rate of variation of distortion effects of the Fermi surface with temperature. The damping of the δ f in the collision integral increases the collisional width of the giant quadrupole resonance (GQR) significantly for small enough values of the relaxation time. The temperature dependence of the eigenenergy of the GQR becomes much weaker than in the corresponding SDA case.