bluuebunny/crossref_metadata_2025 huggingface dataset:
Control ofCruciferaeWeeds in Canola (Brassica napus) with DPX A7881
Authors: Blackshaw Robert E.
Published: May 2019

Postemergence control of broadleaf weeds in canola with DPX A7881 was studied under controlled-environment and field conditions. DPX A7881 controlled weeds of theCruciferaefamily such as wild mustard, field pennycress, and flixweed, which are not controlled with existing herbicides used for weed control in canola. Weed control was better when DPX A7881 was applied at the two-leaf than at the six-leaf stage of the weeds. At the two-leaf stage, control of flixweed was achieved with 15 g ai/ha of DPX A7881; 20 to 30 g ai/ha was required for control of wild mustard and field pennycress. Control of redroot pigweed required 30 g ai/ha. Common lambsquarters was not controlled in this study with DPX A7881 up to 60 g ai/ha. Control of weeds with DPX A7881 increased canola yields in this study without altering the important quality components: oil content, 1000-kernel weight, and green seed content. DPX A7881 provides a postemergence alternative to existing herbicides for broadleaf weed control in canola.
Adsorption of Imazaquin and Imazethapyr on Soils, Sediments, and Selected Adsorbents
Authors: Loux Mark M. , Liebl Rex A. , Slife Fred W.
Published: May 2019

Adsorption of imazaquin and imazethapyr on soils, sediments, clays, and ion exchange resins was studied. Multivariate regression analysis of Freundlich K values and soil and sediment properties yielded a model for imazaquin adsorption which included soil pH, organic carbon, and clay as significant independent variables. Clay content and pH were significant independent variables for the imazethapyr adsorption model. Adsorption of imazaquin and imazethapyr was greater at pH below 6 than at a higher pH. Adsorption of both herbicides on Ca- and H/Al-kaolinite and Ca-montmorillonite was low, but increased on H/Al-montmorillonite. The results of adsorption studies with ion exchange resins indicated that binding of protonated herbicide at low pH could be due to physical forces, hydrogen bonding, or cationic binding. At soil pH levels above the pKa's of imazaquin and imazethapyr, ionic bonding of herbicide anions with positively charged soil components could also occur.
Microencapsulated Alachlor and Its Behavior on Wheat (Triticum aestivum) Straw
Authors: Petersen Brent B. , Shea Patrick J.
Published: May 2019

Scanning electron microscopy (SEM) was used to study alachlor microcapsule morphology and the effects of straw age and moisture on herbicide release. Microcapsule diameter in the formulation ranged from 2 to 15 μm. The polyurea encapsulating material was stable in water over time. Diffusion was suggested as the primary mode of alachlor release, with diffusion rate controlled by herbicide and salt concentration gradients between the microcapsule and the surrounding aqueous solution. Alachlor release was promoted by drying the microcapsules before addition to water. Microcapsule morphology was unchanged 48 h after application to dry straw, and microcapsules did not appear to adhere to the straw surface. Microcapsules applied to overwintered wet straw were shriveled at 48 h after treatment, indicating herbicide loss. Capsule walls were broken and appeared brittle after application to fresh wet straw. Organic constituents of the fresh straw cuticle may affect capsule wall integrity.
Modeling Distributions of Crop and Weed Seed Germination Time
Authors: Bridges David C. , Wu Hsin-I , Sharpe Peter J. H. , Chandler James M.
Published: May 2019

Research was conducted to determine the utility of a single, temperature-independent Weibull function for describing cumulative seed germination under several temperature regimes with 14 sets of weed and crop seed germination data. A modified cumulative Weibull function was derived to distribute germination times for individuals within the population and distributed the occurrence of germination given ample sample size and appropriate sample interval. The descriptive and predictive attributes of the stochastic model component are well suited for incorporation into seed germination models and are likely applicable to models to predict distribution of times for other developmental processes of plants.
Acifluorfen Action on Growth and Phenolic Metabolism in Soybean (Glycine max) Seedlings
Authors: Hoagland Robert E.
Published: May 2019

Three-day-old soybean seedlings were treated with acifluorfen via liquid culture [50 μM in dark, 1 μM in light (200 μE·m–2·s–1)]. Root elongation in the dark was inhibited only slightly (6%) after 96 h. In the light, acifluorfen inhibited root elongation after 48 h; after 96 h, inhibition was 32%. Hypocotyl length was not affected in either the light or dark. Soluble hydroxyphenolic content per axis was unaffected in the dark but was reduced by about 13 to 25% at 24 to 96 h in the light. Extractable phenylalanine ammonia-lyase (PAL, EC 4.3.1.5) activity per axis was unaltered by herbicide in the dark. A brief transient increase in PAL activity (4 to 24 h) in axes of light-grown seedlings in the presence of acifluorfen was followed by reduced enzyme levels compared to light-grown controls at 72 and 96 h. Although light is required for maximal herbicide action, there was no effect on anthocyanin or chlorophyll accumulation or on the chlorophyll a/b ratio in hypocotyls or light-grown seedlings.
Effects of Late-Season Herbicide Applications on Sicklepod (Cassia obtusifolia) Seed Production and Viability
Authors: Isaacs Mark A. , Murdock Edward C. , Toler Joe E. , Wallace Susan U.
Published: May 2019

Application of chlorimuron and imazaquin at 0.28 kg ai/ha to field-grown sicklepod at early bloom and early fruit stages in 1984 and 1985 almost eliminated seed production. In addition, none of the seed produced following these treatments were capable of emergence during a 4-week period following acid scarification. Glyphosate applied at 0.28 kg ai/ha at early bloom decreased seed production 84% but did not affect seedling emergence in 1984, and precluded production of seed capable of emergence in 1985. Glyphosate applications at the early fruit stage reduced the number of seed that emerged 93 and 90% in 1984 and 1985, respectively. Application of 2,4-DB at 0.28 kg ai/ha and 2,4-D at 0.56 kg ai/ha at early bloom did not affect seed production or emergence in 1984 but almost eliminated production of seed capable of emergence in 1985. Applications of 2,4-DB and 2,4-D at the early fruit stage decreased the number of seed that emerged 99 and 52% in 1984 and 46 and 57% in 1985, respectively. Herbicide applications at the late fruit stage were generally less effective than earlier applications in reducing seed production and emergence.
An Alternative Approach for Evaluating the Efficacy of Potential Biocontrol Agents of Weeds. 1. Inverse Linear Model
Authors: Pantone Dan J. , Williams William A. , Maggenti Armand R.
Published: May 2019

Methods for evaluating the efficacy of potential classical biocontrol agents were outlined for a model biocontrol agent-weed-crop system. A proposed biocontrol agent (the fiddleneck flower gall nematode), its weed host (coast fiddleneck), and wheat were used as representative organisms. An additive experimental design (inverse linear model) was used. Regression of the reciprocal of the average plant biomass of each species onto the density of itself and the other plant species yielded competitive indices that measure the competitive ability of the plants. The results of 2 yr of field experiments revealed a dramatic change in the competitive interaction between fiddleneck and wheat due to the nematode. During the 1986–87 season in the absence of the nematode, fiddleneck intraspecific competition was 33 times stronger than interspecific competition with wheat. In the presence of the nematode, intra- and interspecific competition of fiddleneck were nearly equal. Only the coefficients that measure interspecific competition changed significantly in the presence of the nematode while the coefficients for intraspecific competition did not.
An Alternative Approach for Evaluating the Efficacy of Potential Biocontrol Agents of Weeds. 2. Path Analysis
Authors: Pantone Dan J. , Williams William A. , Maggenti Armand R.
Published: May 2019

Path analysis was used to assess the efficacy of the fiddleneck flower gall nematode as a weed biocontrol agent of coast fiddleneck in competition with wheat during 2 yr of field experiments. The path analysis revealed that the number of inflorescences/plant for fiddleneck and the number of heads/plant for wheat were the most important yield components that determine fecundity and seed yield. The density of fiddleneck had a much greater impact on the yield components of fiddleneck than did the density of wheat or the nematode rate of inoculation. The nematode had its greatest negative impact on the number of seeds/flower of fiddleneck and its greatest positive impact on the number of heads/plant of wheat. Path analysis predicts that a biocontrol agent that has a large negative direct effect on the number of inflorescences/plant for fiddleneck would be more efficacious in decreasing fecundity and seed yield than an agent that only impacts the number of flowers/inflorescence, seeds/flower, or biomass/seed.
Recovery of Spring Wheat (Triticum aestivum) Injured by Trifluralin
Authors: Morrison Ian N. , Nawolsky Ken M. , Marshall George M. , Smith Allan E.
Published: May 2019

The relationship between trifluralin dosages detected in the soil at seeding, initial crop injury, and subsequent recovery of spring wheat during the growing season was investigated in field experiments in 1986 and 1987. As the amount of trifluralin in the soil increased, both crop density and dry matter production decreased such that at 1 kg/ha the two were reduced by 37 and 50%, respectively, early in the season. As the season progressed, crop growth rates (CGRs) of wheat in trifluralin-treated plots exceeded those of wheat in the untreated plots. Maximum CGRs occurred between Zadok's growth stages 30 and 45 where trifluralin levels in the soil were 0.3 to 0.5 kg ai/ha at seeding. Recovery from trifluralin injury was characterized by enhanced net assimilation rates of surviving plants, increased tillering and greater dry matter production per plant. Wheat seed yield was only weakly correlated with trifluralin levels in the soil at seeding. From a linear regression model it was determined that a 35% reduction in plant dry weight from the trifluralin injury at the beginning of tillering would result in no more than a 10% reduction in seed yield at final harvest.
Fluazifop Toxicity to Quackgrass (Agropyron repens) as Influenced by Some Application Factors and Site of Application
Authors: Chandrasena Nimal R. , Sagar Geoff R.
Published: May 2019

The phytotoxicity of the butyl ester of fluazifop to quackgrass was enhanced by the addition of a nonionic surfactant and an oil additive either alone or in mixture to the spray solution. The enhancement caused by the surfactant was consistently greater than that caused by the oil additive. A higher level of quackgrass control was achieved at the carrier volumes of 100, 200, or 400 L/ha, than at 800 L/ha. Quackgrass growth inhibition was greater following application of small herbicide droplets which averaged 0.25 μl compared to larger herbicide droplets at each herbicide application rate. When droplet concentration was varied and different doses of the herbicides applied to plants, no significant differences were noted at the highest dose. However, at intermediate dose treatments, the least concentrated droplets (2.5 μg/μl) were most phytotoxic. Herbicide droplets placed at basal areas of leaves were more phytotoxic than when placed at lamina apices and middle areas. This effect was most pronounced on adaxial rather than abaxial surfaces. In general, application of droplets to younger leaves resulted in greater phytotoxicity than treatment of older leaves.
Biodegradation Characteristics of Imazaquin and Imazethapyr
Authors: Cantwell John R. , Liebl Rex A. , Slife Fred W.
Published: May 2019

The extent of14C-imazaquin and14C-imazethapyr abiotic vs. biotic degradation in soil was investigated. Degradation was measured in an in vitro system which allowed 90% recovery of applied herbicide. Triallate biodegradation is well documented and therefore used as a standard. Herbicide degradation was compared in two soils, a Cisne silt loam and a Drummer silty clay loam. Herbicide degradation in gamma-irradiated soil was compared to fresh soil. Biomass quantities were measured for the duration of the experiments.14CO2evolution, extractable parent, metabolites, and unextractable residue were measured. After 12 weeks of incubation, 95% of the radioactivity could be extracted as parent from sterilized soil. In unsterilized soil, imazaquin and imazethapyr degraded at a similar rate which was dependent upon soil type. All herbicides degraded slower in the Drummer soil and triallate degraded two to three times faster than the imidazolinones in either soil.14C-imazaquin degradation products included14CO2and unextractable residues. The major product from14C-imazethapyr degradation was14CO2. Evolution of14CO2from an imazethapyr-treated Cisne soil, containing a serial dilution of activated charcoal, demonstrated that adsorption of herbicide was negatively correlated with degradation. Therefore imidazolinone microbial degradation is regulated by the amount of herbicide in soil solution as determined by soil characteristics.
Effects of Imazaquin Residues on Cotton (Gossypium hirsutum)
Authors: Barnes Clyde J. , Goetz Andrew J. , Lavy Terry L.
Published: May 2019

Field and laboratory studies were conducted in 1987 and 1988 on several Arkansas soils to determine the effects of residual levels of imazaquin on cotton. Imazaquin concentrations ranging from 0.007 to 0.024 μg/g and 0.00 to 0.015 μg/g were found in soil samples taken 12 and 24 months, respectively, following preplant-incorporated applications at rates of 140 g/ha. Cotton yields were reduced from 7 to 42% in 1987 as the soil concentration of imazaquin increased from 0.007 to 0.024 μg/g. Imazaquin persistence was greater in clay soils than loams or sandy loams. Imazaquin was weakly adsorbed to a clay, loam, and sandy loam soil in laboratory studies; the adsorption isotherms did not differ significantly by soil texture. A bioassay utilizing cotton as the indicator species was developed to determine imazaquin concentrations in soils ranging from 0 to 0.06 μg/g. Imazaquin concentrations determined by the bioassay method were found to be 75, 77, and 80% of those determined by chemical extractions for a clay, loam, and sandy loam soil, respectively.
Phytotoxicity of 2,4-D and 2,4-Dichlorophenol to Red Clover (Trifolium pratense)
Authors: Taylor S. G. , Shilling D. G. , Quesenberry K. H. , Chaudhry G. R.
Published: May 2019

Whole plant and tissue culture experiments were conducted to determine the difference in phytotoxicity of 2,4-D and its metabolite, 2,4-DCP, to red clover. At the whole plant level, the mean concentration of 2,4-DCP (10 mM) required to cause 50% growth inhibition (I50) of shoot dry weight was 24 times greater than for 2,4-D (0.42 mM). Using callus tissue, the I50value for 2,4-DCP (0.28 mM) was 22 times greater than for 2,4-D (0.013 mM) based on dry weights. The callus tissue was 36 and 32 times more sensitive to 2,4-DCP and 2,4-D than shoot tissue based on dry weights, respectively. These data indicate that 2,4-DCP was less phytotoxic than 2,4-D to red clover both in vitro and in vivo.
Efficacy ofPhomopsis convolvulusfor Control of Field Bindweed (Convolvulus arvensis)
Authors: Morin Louise , Watson Alan K. , Reeleder Richard D.
Published: May 2019

Phomopsis convolvulusOrmeno, a fungus, reduced growth and regeneration of field bindweed under greenhouse environments. Field bindweed seedlings at the cotyledon stage were severely injured and killed (95% mortality) with 108conidia/m2. Three- to five-leaf seedlings (2 weeks old) were controlled when inoculated with 109conidia/m2(70% mortality; 98 and 89% reduction in dry weight of aboveground biomass and roots, respectively). This inoculum density reduced aboveground and root biomass, and adversely affected regeneration of 4-week-old seedlings and established plants, but few plants were killed. In controlled-environment studies, two inoculations were superior (P = 0.02) to one inoculation in reducing foliage aboveground of well-established seedlings (4 weeks old). However, new shoots produced between the first and second inoculation treatments were less diseased than expected.
A New Method for Estimating Seed Numbers in the Soil
Authors: Gross Katherine L. , Renner Karen A.
Published: May 2019

An elutriation system was developed to estimate weed seed densities in soil. The system provided reliable estimates of seed densities for weed species with a broad range of seed weights (0.06 to 9.80 mg) and had no effect on seed viability of three weed species tested. Elutriation of soil samples (up to 60 g) taken from a cultivated field took approximately 15 min. Separating, classifying, and counting seeds is time consuming (20 to 30 min per sample) but provides an accurate estimate of seed densities for weeds with a diameter of 0.5 mm or more.
Physiological Competence of Atrazine-Resistant Strains of the Photosynthetic BacteriumRhodobacter sphaeroides(Rhodospirillaceae)
Authors: Brown Alfred E. , Truelove Bryan , Highfill Claudia T. , Smith Scott G.
Published: May 2019

Two parameters of physiological competence, rate of CO2fixation and intraspecific competitiveness, were determined for one or more atrazine-resistant isolates of the photosynthetic bacteriumRhodobacter sphaeroides. Measured over a 2-h period under optimal conditions, two of the resistant isolates fixed CO2at a greater rate than the atrazine-susceptible, wild-type organism. In a mixed culture study, an atrazine-resistant strain was able to grow and compete successfully with the susceptible, wild-type strain for at least 14 days.
Strigol Analogs as Germination Regulators in Weed and Crop Seeds
Authors: Pepperman Armand B. , Bradow Judith M.
Published: May 2019

Twelve analogs of the strigol D-ring (butenolides) were evaluated at 0.1 mM as germination regulators of 26 weed and crop seeds. In general, the butenolides either inhibited or did not affect monocot germination, although the hydroxybutenolide stimulated germination of dormant cheat and nondormant perennial ryegrass and sorghum seeds. The response rate for dicots was greater but still primarily inhibitory. Dormant lettuce seeds (both light-sensitive and light-insensitive), Palmer amaranth, and redroot pigweed showed several significant responses, both inhibitory and stimulatory. Some of the butenolides that had not been previously assayed against witchweed were tested as 10-4to 10-11M dilution series. The allyloxybutenolide demonstrated activity comparable to strigol (30 to 60% germination at 10-6to 10-11M); the sec-butyloxybutenolide was somewhat less active (20 to 40% germination) but still effective at 10-9M. In general, the butenolide analogs of strigol were less effective in stimulating seed germination than the multiring analogs.
Taxonomic Evaluation of Leaf and Latex Variability of Leafy Spurge (Euphorbiaspp.) for Montana and European Accessions
Authors: Harvey Stephen J. , Nowierski Robert M. , Mahlberg Paul G. , Story Jim M.
Published: May 2019

Leafy spurge (Euphorbiaspp.), an aggressive noxious perennial weed of North America, is a complex group that has been designated as several different species, includingE. esulaL. (# EPHES) andE. virgataWald. & Kit. [E. waldsteinii(Sojak) Radcliffe-Smith]. Current classification keys are unsatisfactory in assigning plants in the field to specific taxa (or to a single taxon). These keys rely heavily upon morphological characteristics of leaves, but great variation in the leaves has been noted by us and previously reported by others. In this study we demonstrate qualitatively and quantitatively that the within-plant, within-clone, among-clone, and among-site variation in leaf morphology and triterpenoid content of the latex of leafy spurge is inherently high. Leaf characters were of little value in separating any of the accessions considered in our study. Latex triterpenoid profiles were useful in distinguishingE. lucidaW. & K. ×salicifoliaHost. andE. salicifoliafrom EuropeanE. esula, E. waldsteinii, andE. sequierianaNeck. ssp.seguieriana, and all Montana accessions previously described from morphological studies. We concluded that Montana leafy spurge and the EuropeanE. esula, E. waldsteinii, andE. sequierianabelong to a single taxon:Euphorbia esulaL.
Volunteer Barley (Hordeum vulgare) Interference in Canola (Brassica campestrisandB. napus)
Authors: O'Donovan John T. , Sharma Arvind K. , Kirkland Ken J. , De St. Remy E. Ann
Published: May 2019

The yield potential and the effect on yield loss of canola of different densities of volunteer barley were investigated at three locations in western Canada. Field studies were conducted from 1982 to 1986. Rectangular hyperbolic models based on data pooled over years, locations, and canola cultivars, and incorporating different densities of volunteer barley and canola accurately portrayed field responses in most instances. Results indicated that volunteer barley severely reduced canola yield. However, financial losses due to reduced canola yield were partly offset by the volunteer barley crop.
Soil Water Relations of Silverleaf Nightshade (Solanum elaeagnifolium) with Cotton (Gossypium hirsutum)
Authors: Green J. D. , Murray Don S. , Stone John F.
Published: May 2019

Dryland and irrigated field experiments were established to measure differences in soil water relations throughout the growing season between plots in which cotton was grown with and without silverleaf nightshade interference. Soil moisture readings were taken weekly at 15-cm increments to a maximum depth of 120 and 150 cm during 1984 and 1985, respectively. When cotton was grown with silverleaf nightshade, soil water loss was greater at the lower portion of the soil profile earlier in the growing season than when cotton was grown alone. In the irrigated environment in 1985 when precipitation was higher than normal and the soil moisture content remained above normal, soil water loss did not differ. Cotton lint yield, plant height, and boll size reflected the amount of soil moisture available for growth and development of the crop. A statistical technique for quantifying soil water relations between the crop growing alone and growing with interference from the weed is demonstrated.
Development of Common Milkweed (Asclepias syriaca) Root Buds Following Emergence from Lateral Roots
Authors: Stamm-Katovich Elizabeth J. , Wyse Donald L. , Biesboer David D.
Published: May 2019

In common milkweed, the development of subterranean root buds on excised root segments, following emergence from the parent root, is characterized by development of nodes and internodes followed by internode expansion. Transverse sections of root buds reveal that bicollateral vascular bundles as well as leaf traces and gaps are well developed in buds from 3-month-old plants. Strands of xylem and phloem connect the parent root and root bud in both inhibited and noninhibited root buds. Pitted primary tracheary elements, characteristic of developmentally advanced primary xylem, are present in these traces. The occurrence of a well-developed vascular system throughout the root bud and between the parent root and bud provides evidence that retardation of growth of inhibited root buds in common milkweed is not caused by anatomical constraints.
Interference of Four Annual Weeds in Corn (Zea mays)
Authors: Beckett Thomas H. , Stoller Edward W. , Wax Loyd M.
Published: May 2019

Season-long interference of shattercane, giant foxtail, common cocklebur, and common lambsquarters in corn was evaluated in the field at weed densities from 0.4 to 13.1 plants or clumps/m of corn row during 1985, 1986, and 1987. Corn seed yields decreased linearly with increases in the density of clumps of 2 to 3 shattercane plants and 5 to 8 giant foxtail plants, reaching 22% yield loss at 6.6 shattercane clumps/m of row and 18% yield loss at 13.1 giant foxtail clumps/m of row. Increases in common cocklebur density caused corn yields to decrease curvilinearly in 1985 with a maximum predicted yield loss of 27% occurring at a density of 4.7 common cocklebur plants/m of row. In 1986 and 1987, yields decreased linearly as common cocklebur density increased to 6.6 plants/m of row, where a 10% yield loss was observed. Common lambsquarters reduced corn yields only in 1985. In this year, yields decreased curvilinearly with increasing weed density, resulting in a maximum yield loss of 12% at 4.9 common lambsquarters plants/m of row. Corn yields averaged 11600 kg/ha when grown without weed interference in these experiments.
Effects of Barnyardgrass (Echinochloa crus-galli) on Growth, Yield, and Nutrient Status of Transplanted Tomato (Lycopersicon esculentum)
Authors: Bhowmik Prasanta C. , Reddy Krishna N.
Published: May 2019

Field studies were conducted to determine the effects of various barnyardgrass populations on growth, yield, and nutrient concentration of transplanted “Jetstar’ tomato. Barnyardgrass densities at 16, 32, and 64 plants/m tomato row were tested in 1982 and 1983. Barnyardgrass shoot fresh weights/unit area increased as density increased. Fresh weight of barnyardgrass shoots ranged from 17 100 kg/ha at 16 plants/m of row to 35 500 kg/ha at 64 plants/m of row. At the vegetative stage, tomato shoot dry weight was unaffected by barnyardgrass. As crop growth progressed, tomato shoot dry weight decreased at all barnyardgrass densities. Season-long interference of barnyardgrass reduced marketable tomato fruit number and fruit weight at all densities compared to weed-free plots. Reductions in marketable fruit weight ranged from 26% to 16 plants/m row to 84% at 64 plants/m row. In 1982, concentrations of N, P, K, Ca, and Mg in tomato shoots were unaffected by season-long interference of barnyardgrass at all densities. However, in 1983, concentrations of N and K decreased and concentration of P increased in tomato leaves as the density of barnyardgrass increased. Concentrations of Ca and Mg in tomato leaves were unaltered by barnyardgrass density.
Effect of Light on Growth and Development of Field Bindweed (Convolvulus arvensis) and Russian Knapweed (Centaurea repens)
Authors: Dall'Armellina Armando A. , Zimdahl Robert L.
Published: May 2019

Field bindweed and Russian knapweed were grown from seed or rhizome segments under 520, 325, or 236 μmol·m–2· s–1photosynthetic photon flux density (PPFD) to determine vegetative and reproductive response. Flower production in both species declined with decreasing light level. Leaf area of field bindweed decreased as light level decreased, but Russian knapweed leaf area increased as light intensity decreased from 520 to 325 μmol·m–2·s–1PPFD or from 520 to 236 μmol·m–2·s–1. Dry matter of shoots, roots, and rhizomes of field bindweed grown from seed declined as light level decreased, but the only response of plants grown from rhizome segments was complete inhibition of rhizome production. Dry matter of Russian knapweed shoots and roots in plants grown from seed or rhizome segments decreased as light decreased. In both species the total PPFD was more important than whether low or high light level occurred first.
Release of Postsenescent Dormancy in Leafy Spurge (Euphorbia esula) by Chilling
Authors: Harvey Stephen J. , Nowierski Robert M.
Published: May 2019

The growth and development of leafy spurge (Euphorbia esulaL. #3EPHES) collected during postsenescent dormancy and grown in the greenhouse was increasingly stimulated by chilling treatments longer than 14 days duration at 0 to 6 C. Production of stems with flower buds, primary flowers, and secondary flowers was greater in plants chilled for 42 days or more. The effects of chilling on total number of stems, number of strictly vegetative stems, or number of stems with vegetative branching were not significant. The height of the tallest stem per pot was influenced by chilling longer than 42 days. Growth rate also increased as a function of chilling duration. Based on our findings, we believe that there is little possibility that any significant growth can occur in the postsenescent period because of the prevailing climatic conditions found in areas of leafy spurge distribution in North America.
Germination and Seed Production of Unicorn-Plant (Proboscidea louisianica)
Authors: Riffle Michael S. , Thilsted W. Eugene , Murray Don S. , Ahring Robert M. , Waller George R.
Published: May 2019

Field and laboratory experiments were conducted with unicorn-plant to determine conditions required for germination and to measure seed production. Field-grown plants produced an average of 122 pods/plant with an average of 71 seed/pod. The highest percent germination from seed harvested in 1980 occurred following a 2-week prechill treatment of 4 C. Germination increase was greater by removing the seed coat and the membrane enclosing the embryo than by removing the seed coat alone. Germination of seed from all pod compartments was similar. Aqueous extracts of unicorn-plant testa, leaf, stem, root, and exocarp were inhibitory in petri dish bioassays to cotton radicle growth. Extracts of stem, root, and exocarp were inhibitory to wheat radicle growth, and extracts of endocarp, leaf, and exocarp were inhibitory to unicorn-plant radicle growth. Seed buried in the field 10 cm deep for 1 to 8 months showed increased germination over time. Germination was lower when seed were stored at 4 C for 1 to 8 months in a soil having 25% (v/v) water.
Influence of Thiameturon and DPX-L5300 on Wild Oats (Avena fatua) Control with Barban, Diclofop, AC 222,293, and Difenzoquat
Authors: Eberlein Charlotte V. , Miller Timothy L. , Wiersma John V.
Published: May 2019

In field studies, wild oat control with AC 222,293 and difenzoquat was not reduced when each herbicide was applied in combination with thiameturon or DPX-L5300. Mixtures of barban with thiameturon gave wild oats control similar to barban applied alone, but mixtures of barban with DPX-L5300 sometimes gave less wild oats control than barban applied alone. Control was reduced when diclofop was applied in combination with thiameturon in 1985 but not in 1986. When antagonism occurred, addition of crop oil concentrate (COC) at 1.2 L/ha to the diclofop-thiameturon spray mixture overcame the antagonism. When diclofop was applied in combination with DPX-L5300, control was reduced and antagonism could not be overcome by increasing the diclofop rate or by adding COC to the spray mixture. In greenhouse studies the inert ingredients in the thiameturon and DPX-L5300 formulations did not antagonize diclofop activity on wild oats. TLC analysis of14C-diclofop solutions with and without thiameturon or DPX-L5300 revealed neither degradation products of diclofop nor evidence of complexing between diclofop and thiameturon or diclofop and DPX-L5300. Diclofop antagonism by thiameturon or DPX-L5300 was not due to a chemical or physical interaction between the herbicides in the spray mixture.
Clopyralid Effects on Shoot Emergence, Root Biomass, and Secondary Shoot Regrowth Potential of Canada Thistle (Cirsium arvense)
Authors: Donald William W.
Published: May 2019

The root fresh weight of intact Canada thistle plants was greater than that of decapitated plants 2 months following soil surface treatment with clopyralid at 140 g ai/ha. Nevertheless, secondary shoot regrowth potential was reduced to the same extent for both intact and decapitated plants after clopyralid treatment. Soil-applied clopyralid did not reduce root biomass as much as it reduced secondary shoot regrowth potential from adventitious root buds. Increasing the clopyralid rate from 11 to 1120 g/ha progressively reduced the total number of emerged shoots more than root fresh weight 2 months after treatment of decapitated Canada thistle. Increasing the clopyralid rate also reduced the regrowth potential of secondary shoots from root buds proportionately more than it reduced root biomass. Secondary shoots emerging through a surface layer of soil treated with clopyralid at 140 g/ha absorbed phytotoxic amounts of clopyralid. Secondary shoot numbers were not reduced after emerging through an activated charcoal layer into herbicide-treated soil, but they were deformed and their dry weight was reduced as was later secondary shoot regrowth potential.
Conditions Influencing Turbinella Oak (Quercus turbinella) Mortality from Picloram or Picloram and 2,4-D
Authors: Johnsen Thomas N.
Published: May 2019

Turbinella oak was sprayed with picloram-containing herbicides on 90 dates throughout 81 months. A mixture of triisopropanolamine salts of picloram and 2,4-D was compared to the potassium salt of picloram on 44 dates, and to a mixture of isooctyl ester of picloram and propylene glycol butyl ether esters of 2,4-D on 42 dates. Low rates of herbicide treatments were used to increase the sensitivity to environmental factors and plant growth stages. Turbinella oak mortality was greater with the mixture of picloram and 2,4-D amines than with picloram alone or the mixture of picloram and 2,4-D esters. The mixture of picloram and 2,4-D esters did not kill any plants. The combination of available soil moisture at the 60-cm depth, no senescent or falling leaves, and full-sized leaves was the best indicator of when to apply picloram or the mixture of picloram and 2,4-D amines. No turbinella oak were killed when soil at the 60-cm depth was dry or leaves were falling at the time of treatment.
Biodegradation of Carbamothioates in Butylate-History Soils
Authors: McCusker Vicki W. , Skipper Horace D. , Zublena Joseph P. , Gooden Dewitt T.
Published: May 2019

Laboratory experiments were conducted to evaluate the biodegradation of14C-labeled butylate, cycloate, EPTC, pebulate, and vernolate in three butylate-history soils that had received three to eight applications of butylate under field conditions. After 20 days, biodegradation of butylate and EPTC was accelerated and had no lag phase in all three butylate-history soils. Butylate-adapted microorganisms were cross-adapted for EPTC and degraded EPTC as readily as butylate. Biodegradation of butylate and EPTC in Dothan soil without a butylate history exhibited a lag phase of 6 days after which14CO2was evolved at an exponential rate. This indicated that enhanced biodegradation was induced after one application of butylate or EPTC. Butylate-adapted microorganisms were cross-adapted for vernolate and pebulate in Dothan and pebulate in Wagram soils with a butylate history. Biodegradation of vernolate and pebulate was not enhanced in Varina butylate-history soil. After 20 days, there was no cross-adaptation for cycloate in any soil. These findings indicated that biodegradation of carbamothioates was influenced by soil type and previous carbamothioate use and that caution should be exercised in use of EPTC on fields of previous butylate use.
Comparison of Soybean (Glycine max) – Weed Interference from Large and Small Plots
Authors: Patterson Michael G. , Walker Robert H. , Colvin Daniel L. , Wehtje Glenn , McGuire John A.
Published: May 2019

Soybean field experiments were conducted to compare weed interference data obtained from small 2.7-m2plots to that obtained from large 11-m2plots. Soybean row spacings of 15, 30, 45, and 90 cm were used. Sicklepod, common cocklebur, and soybean biomass as dry matter were harvested from small plots 10 weeks after planting and were compared to weed biomass and soybean seed yield from the large plots. Sicklepod and common cocklebur biomass in small plots increased and soybean biomass decreased as soybean row spacing increased. Soybean biomass was not affected by row spacing when weeds were not present. Sicklepod and common cocklebur biomass in large plots increased and soybean seed yield decreased as soybean row spacing increased. Soybean seed yield was not affected by row spacing when weeds were not present. Comparison of regression coefficients for paired regression lines indicates that soybean biomass from small plots may be substituted for seed yield from large plots as a measure of sicklepod or common cocklebur interference if both size plots use the same soybean row spacing and are irrigated until harvest.
Systems Approach to Weed Management in Irrigated Crops
Authors: Schweizer Edward E. , Lybecker Donald W. , Zimdahl Robert L.
Published: May 2019

The impact of four weed management systems on weed seed reserves in soil, yearly weed problem, and production of barley, corn, pinto bean, and sugarbeet was assessed where these crops were grown in rotation for 4 consecutive years in four cropping sequences. Weeds were controlled in each crop with only conventional tillage or conventional tillage plus minimum, moderate (system 1), and intensive (system 2) levels of herbicides. Seed of annual weeds from 11 genera were identified, with barnyardgrass and redroot pigweed comprising 66 and 19%, respectively, of the initial 90 million weed seed/ha present in the upper 25 cm of the soil profile. After the fourth cropping year, overall decline in total number of weed seed in soil was 53% when averaged over four cropping sequences and four weed management systems. Over the 4-yr period, about 10 times more weeds escaped control in system 1 than in system 2; and within a crop, the fewest number of weeds escaped control annually in barley. System 2 had the highest herbicide use in each cropping sequence, the fewest weeds at harvest, and the smallest adjusted gross return over the 4-yr period in three of four cropping sequences.
Economic Analysis of Four Weed Management Systems
Authors: Lybecker Donald W. , Schweizer Edward E. , King Robert P.
Published: May 2019

An economic analysis of four weed management systems employed on four crop sequences in a barley-corn-pinto bean-sugarbeet rotation in eastern Colorado was computed. Weeds were controlled in each crop with only conventional tillage or conventional tillage plus minimum levels of herbicides (systems 3 and 4), moderate levels of herbicides (system 1), or intensive levels of herbicides (system 2). Adjusted gross returns were higher for systems 3 and 4 where herbicide use was less/year and decreased over 4 yr than for systems 1 and 2 where herbicide use was higher/year and constant. When the four crop sequences were aggregated using yield and sucrose indices, the least herbicide-intensive weed management system had $440/ha/4 yr higher indexed adjusted gross return than the most herbicide-intensive weed management system. An income risk analysis showed that the herbicide-intensive weed management system was not risk efficient and that producers would select one of the other three less herbicide-intensive weed management systems depending upon their risk preferences.
SCHUMPETER E IL DIBATTITO SULLA TEORIA «COMPETITIVA» DELLA DEMOCRAZIA
Authors: Ferrera Maurizio
Published: May 2019

Introduzione

Insieme a Michels, Mosca e Pareto, Schumpeter è comunemente annoverato tra i pensatori che più hanno contribuito, nel nostro secolo, ad approfondire ed articolare il concetto di «democrazia» e, più in particolare, il nesso che lega in un sistema democratico le élites governanti ai propri governati. La quarta parte diCapitalismo, Socialismo e Democraziaè una lettura obbligata per ogni studioso del regime democratico, non importa se mosso da intenti prescrittivi o descrittivi.
PARTITI E CAMBIAMENTO POLITICO NEGLI USA (1968-1988): UN CASO DI RIFORMA ISTITUZIONALE
Authors: Fabbrini Sergio
Published: May 2019

Introduzione

Lo scopo di questo saggio è quello di analizzare la riforma del sistema di selezione del candidato presidenziale attuata negli Stati Uniti tra il 1968 e il 1988. Data la rilevanza che ha avuto ed ha, per i partiti politici statunitensi, la scelta del candidato presidenziale, l'analisi della riforma del sistema di selezione può consentire di individuare i cambiamenti realizzatisi sia nell'organizzazione di quei partiti che nel ruolo da essi esercitato nel sistema politico.
LA NUOVA PARTECIPAZIONE NELLE SOCIETà POST-INDUSTRIALI
Authors: Inglehart Ronald
Published: May 2019

Introduzione

Lo sviluppo economico dovrebbe condurre a crescenti livelli di partecipazione politica di massa per almeno tre buoni motivi teorici: 1) i cittadini delle società industriali avanzate hanno visto migliorare le loro capacità di partecipare: durante l'ultimo mezzo secolo i loro livelli di istruzione si sono accresciuti in modo impressionante e la formazione politica si è fatta più facilmente accessibile; 2) le norme sociali si sono fatte più permissive verso la partecipazione politica della metà femminile della popolazione. Una o due generazioni fa le donne non avevano neanche il diritto di voto. Oggi, non solo lo hanno acquisito in tutte le democrazie occidentali, ma vi è anche una crescente accettazione informale del fatto che esse debbano giocare un ruolo politico uguale a quello degli uomini e si sono diffusi i modelli di ruolo politico femminile. Infine, 3) vi sono segnali che le priorità valoriali del pubblico occidentale siano venute gradualmente passando da valori materialisti a valori postmaterialisti. Questo trend dovrebbe contribuire ad una crescita del tasso di partecipazione politica: liberatisi dalla necessità di concentrare le loro energie in via prioritaria nella lotta per la sicurezza economica e fisica, i cittadini dovrebbero essere in grado di dedicare più attenzione a preoccupazioni postmaterialistiche come la politica.
LE COALIZIONI REGIONALI IN ITALIA
Authors: Motta Riccardo
Published: May 2019

Introduzione

Scopo di questo articolo è analizzare i processi politici che danno luogo alla formazione delle coalizioni nei sistemi politici locali. Tranne rare eccezioni, le teorie delle coalizioni hanno privilegiato come campo di indagine i governi nazionali, e su di essi ne è stata verificata la capacità predittiva. Le ricerche empiriche fino ad oggi effettuate consentono una valutazione di tali teorie e la individuazione dei punti deboli; restano però, per molti versi, sconosciuti i problemi che pongono i comportamenti coalizionali all'interno delle assemblee elettive locali. In particolare, la domanda che si pone è se esistano problemi specifici, al di là di quelli conosciuti, finora trascurati e, tuttavia, importanti. A questi interrogativi si darà una risposta nel corso di questo articolo applicando la teoria delle coalizioni sulle giunte delle prime tre legislature delle regioni a statuto ordinario.
RAPPRESENTANZA E PARLAMENTO EUROPEO
Authors: Bardi Luciano
Published: May 2019

Introduzione

Uno degli interrogativi principali posti dalle elezioni a suffragio universale del Parlamento Europeo riguarda la loro capacità di fornire, se non immediatamente almeno nel medio periodo, una legittimità autonoma alla Comunità Europea. Sul piano analitico, questo significa che per uno studio sull'evoluzione della Comunità occorre stabilire se il Parlamento direttamente eletto riuscirà a sostituirsi alle fonti attuali (essenzialmente i governi nazionali) nel fornire legittimità alle azioni di governo europeo.
DEMOCRAZIA E COMPETIZIONE
Authors: D'Alimonte Roberto
Published: May 2019

Introduzione

Secondo Schumpeter la democrazia politica o, meglio, il metodo democratico è «quello strumento istituzionale per arrivare a decisioni politiche nel quale alcune persone acquistano il potere di decidere mediante una lotta per il voto popolare» (Schumpeter 1973, 257). È su questa definizione che poggia la cosiddetta «teoria competitiva della democrazia». La sua novità; e rilevanza sta nel fatto che la democrazia viene identificata nelprodottodella competizione traélitespolitiche. In altre parole, la democrazia rappresentativaderivadal fatto che il potere di scegliere tra i partiti in competizione è nelle mani del popolo. Il popolo non decide quindi sulle cose, ma decide solo su chi debba decidere. La competizione tra i partiti è il meccanismo che assicura al popolo questo potere e perciò la sua sovranità.
IL CLIENTELISMO NEL TERZO MONDO
Authors: Caciagli Mario
Published: May 2019

Introduzione

Riscoperto dall'antropologia negli anni cinquanta, il clientelismo è stato ormai recepito come consolidata categoria analistica dalle altre scienze sociali, in particolare dalla scienza politica, dove si è venuto definitivamente affermando negli ultimi vent'anni. Serve a studiare rapporti informali di potere, basati sullo scambio di favori fra due persone (ma anche fra due gruppi) in posizione diseguale, ciascuna interessata ad un alleato più forte o più debole. È stato definito come un «rapporto diadico» (Scott 1972; Landé 1973), in virtù del quale una persona di status più elevato(patrono) usa la sua influenza e le sue risorse per procurare protezione e benefici ad una persona di status inferiore (cliente), che ricambia offrendo sostegno o servizi.
SCIENZA POLITICA E TEORIA DELL'ORGANIZZAZIONE. LE POSSIBILI CONVERGENZE
Authors: Olsen Johan P.
Published: May 2019

Introduzione

Che cosa possono sperare di imparare gli studiosi della politica dando maggiore attenzione alla teoria dell'organizzazione? In questo dopoguerra questa domanda ha ricevuto il più delle volte una risposta pessimistica. Gli scienziati politici non hanno mostrato una tendenza a considerare la teoria dell'organizzazione particolarmente rilevante, interessante o importante. Nonostante ci sia stato qualche significativo esempio di fertilizzazione incrociata, la maggior parte degli osservatori concluse che teoria dell'organizzazione e scienza politica si sono trovate per anni in uno stato di reciproco disinteresse.
RIVOLUZIONI E BUROCRAZIE. QUATTRO CASI A CONFRONTO
Authors: di Cortona Pietro Grilli
Published: May 2019

Introduzione

Uno degli argomenti critici più noti nei confronti delle rivoluzioni è che queste conducono ad un maggior dominio burocratico, reso inevitabile da una nuova centralizzazione del sistema e dall'estensione del controllo statale sull'economia. La tesi della degenerazione burocratica delle rivoluzioni, come formazione di nuove stasi e inflessibilità strutturali capaci di frenarne la spinta propulsiva originaria, è dominante, per esempio, anche nella polemica condotta da molti critici marxisti del sistema sovietico che, da Trockij in poi, sottolineano come questo abbia «tradito» gli ideali della rivoluzione bolscevica.
LA SICUREZZA EUROPEA DOPO IL TRATTATO SUGLI EUROMISSILI: LA PROSPETTIVA AMERICANA
Authors: Terzuolo Eric R.
Published: May 2019

Introduzione

È abbastanza naturale che il Trattato INF sugli Euromissili firmato a Washington l'8 dicembre 1987 abbia aperto un ampio dibattito sui problemi del futuro della difesa europea. Infatti, il Trattato è ricco di nuovi elementi che rappresentano una rottura rispetto ai paradigmi consolidati nel campo del controllo degli armamenti. Anche osservatori normalmente critici verso l'amministrazione Reagan hanno ammesso che il Trattato INF creerà condizioni e prospettive nuove «eliminando una intera categoria di armi in cui entrambe le parti avevano effettuato investimenti economici e politici di grande rilievo, imponendo riduzioni asimmetriche al fine di raggiungere un risultato finale equo, stabilendo clausole di verifica precise e a carattere «intrusivo» e dimostrando che la strategia di «armarsi per discutere» può avere successo».
LA DEMOCRAZIA RIVISITATA DA SARTORI: UNA NOTA
Authors: Sola Giorgio
Published: May 2019

Introduzione

L'uscita diThe Theory of Democracy Revisited(Chatham, N.J., Chatham House, 1987, 2 voll.) è un avvenimento di grande rilievo, non solo per la comunità politologica internazionale, ma anche per un pubblico colto ed informato. La ragione principale consiste nel fatto che questa opera di oltre cinquecento pagine rappresenta il punto di arrivo e la sintesi di trent'anni di studi e di ricerche condotte da Giovanni Sartori nel campo della politica, con particolare riguardo ai problemi del metodo, allo studio dei partiti e dei sistemi di partito, all'edificazione di una teoria della democrazia in cui trovino coerente collocazione sia gli aspetti descrittivi che quelli prescrittivi, sia le aspirazioni che le valutazioni che accompagnano questo termine fin dal suo apparire nel IV secolo a.C.