bluuebunny/crossref_metadata_2025 huggingface dataset:
Orthotic Design through 3D Reconstruction: A Passive‐Assistance Ankle–Foot Orthotic
Authors: Darling A. L. , Sun W.
Published: July 2006

Current methods of designing and manufacturing custom orthotics include manual techniques such as casting a limb in plaster, making a plaster duplicate of the limb to be treated and forming a polymer orthotic directly onto the plaster model. Such techniques are usually accompanied with numerous postmanufacture alterations to adapt the orthotic for patient comfort. External modeling techniques rely heavily on the skill of the clinician, as the axes of rotation of any joint are partially specified by the skeletal structure and are not completely inferable from the skin, especially in cases where edema is present. Clinicians could benefit from a simultaneous view of external and skeletal patient‐specific geometry. In addition to providing more information to clinicians, quantification of patient‐specific data would allow rapid production of advanced orthotics, requiring machining rather than casting. This paper presents a supplemental method of orthotic design and fitting, through 3D reconstruction of medical imaging data to parameterise an orthotic design based on a major axis of rotation, shape of rigid components and placement of skin contact surfaces. An example of this design approach is shown in the design of an ankle–foot orthotic designed around the computed tomography data from the Visible Human Project.
Evaluation of Morphological and Functional Nerve Recovery of Rat Sciatic Nerve with a Hyaff11‐Based Nerve Guide
Authors: Jansen K. , Ludwig Y. , van Luyn M. J. A. , Gramsbergen A. A. , Meek M. F.
Published: July 2006

Application of a Hyaff11‐based nerve guide was studied in rats. Functional tests were performed to study motor nerve recovery. A withdrawal reflex test was performed to test sensory recovery. Morphology was studied by means of histology on explanted tissue samples. Motor nerve recovery was established within 7 weeks. Hereafter, some behavioral parameters like alternating steps showed an increase in occurence, while others remained stable. Sensory function was observed within the 7 weeks time frame. Nerve tissue had bridged the 10‐mm gap within 7 weeks. The average nerve fiber surface area increased significantly in time. In situ degradation of the nerve conduit was fully going on at week 7 and tubes had collapsed by then. At weeks 15 and 21, the knitted tube wall structure was completely surrounded by macrophages and giant cells, and matrix was penetrating the tube wall. We conclude that a Hyaff11‐based nerve guide can be used to bridge short peripheral nerve defects in rat. However, adaptations need to be made.
A Novel System for Measuring Optical Properties in Arterial Blood of Man
Authors: Castañeda-Miranda A. , Vizcaya L. D. L.
Published: July 2006

The necessity of man–machine communication has been increasing day by day because of the great number of approaches that help to make human life agile or comfortable. Health is one of the aspects that has generated more interest in recent years. The optical technologies are new technical tools that are being implemented for medical diagnosis and for describing various processes occurring within human blood. These techniques have the virtue of being nondestructive; in addition they have the advantage of remote direction by using an in situ technique, with sensitivity capable of studying the properties of the blood through electromagnetic excitation. A device to obtain the electromagnetic spectrum in the blood has being designed and is presented in this work. This device uses a quartz lamp, emitting electromagnetic radiation between 200 nm and 2200 nm. A model for measuring the light attenuation through the blood is used. By applying a control in the frequency domain, a circuit device is designed. This device uses a database in time domain for its subsequent analysis by Fast Fourier Transformation in order to obtain absorption spectra. The acquisition time is of the order of microseconds, and the system is controlled automatically through accessible software from a personal computer.
Electromyographic Pattern Analysis and Classification for a Robotic Prosthetic Arm
Authors: Erazo Macias M. José H. , Vega S. Alejandro
Published: July 2006

This paper deals with the statistical analysis and pattern classification of electromyographic signals from the biceps of a person with amputation below the humerus. Such signals collected from an amputation simulator are synergistically generated to produce discrete elbow movements. The purpose of this study is to utilise these signals to control an electrically driven prosthetic or orthotic elbow with minimum extra mental effort on the part of the subject. The results show very good separability of classes of movements when a learning pattern classification scheme is used, and a superposition of any composite motion to the three basic primitive motions—humeral rotation in and out, flexion and extension, and pronation and supination. Since no synergy was detected for the wrist movement, different inputs have to be provided for a grip. In addition, the method described is not limited by the location of the electrodes. For amputees with shorter stumps, synergistic signals could be obtained from the shoulder muscles. However, the presentation in this paper is limited to biceps signal classification only.
A Computational Mechatronics Approach for the Analysis, Synthesis and Design of a Simple Active Biped Robot: Theory and Experiments
Authors: Lugo-Villeda L.-I. , Parra-Vega V.
Published: July 2006

Biped walking is a quite complex process that has been mastered only by human beings. Transferring this skill to a robot requires implementing advanced techniques in every aspect. To this end, a computational mechatronics platform was integrated to run the scheme for the analysis, synthesis and design to achieve planar biped walking. The result is an advanced computational tool that integrates advanced modeling and control as well as path planning techniques along with hardware‐in‐the‐loop for perhaps the simplest biped robot. An experimental underactuated three‐degree‐of‐freedom (two active and one passive) active biped robot yields encouraging results; that is, achieving biped walking with this simple device requires adding a telescopic support leg. Considering a more complete dynamic model to take into account frictional and contact forces.
Development of a Multi‐DOF Electromyography Prosthetic System Using the Adaptive Joint Mechanism
Authors: Hernandez Arieta A. , Katoh R. , Yokoi H. , Wenwei Y.
Published: July 2006

This paper describes an electrically powered prosthetic system controlled by electromyography (EMG) signal detected from the skin surface of the human body. The research of electrically powered prosthetic systems is divided into two main subjects. One is the design of the joint mechanism. We propose the use of an adaptive joint mechanism based on the tendon‐driven architecture. This mechanism includes mechanical torque–velocity converters and a mechanism to assist the proximal joint torque by distal actuators. The other subject is the recognition of the EMG signal. For the discrimination of many patterns and nonlinear properties of the EMG signal, we propose a controller based on a simple pattern recognition information process. The system also drives 12 servomotors to move the adaptive joint mechanism. In this paper, we show the proposed system and describe the mechanical design of the prosthetic hand. The experimental results show that the electrically powered devices can be controlled using the proposed method.
Feeding Ecology of Juvenile Lake Sturgeon in the St. Lawrence River System
Authors: Nilo Pedro , Tremblay Serge , Bolon Aline , Dodson Julian , Dumont Pierre , Fortin Réjean
Published: July 2006

We examined the diet of juvenile lake sturgeonAcipenser fulvescensat five sites in the St. Lawrence River, including two sites in major tributaries (Des Prairies and L'Assomption rivers), two main‐stem sites located upstream (Verchères and Sorel‐Berthier islands), and one site located downstream in the estuarine transition zone (ETZ). The benthic fauna was sampled at all sites except in the ETZ. The diets of juvenile lake sturgeon were highly diverse. Of the 74 invertebrate prey taxa identified, approximately 50 occurred in more than 5% of the stomach contents. Most of these prey taxa were of small size. In the three sites where the same sampling strategy and techniques were used, diet varied significantly with sampling site and month. In addition, diet varied significantly with fish length but independently of site and month. Lake sturgeon from the Verchères Islands exhibited the highest diet diversity, and fish situated in the ETZ exhibited the lowest. Except for one of the five sites (L'Assomption River), diet was dominated by amphipods. Chironomids predominated at L'Assomption River and were the second most numerous at the Verchères Islands, Sorel‐Berthier Islands, and Montmagny sites. Other important prey were oligochaetes, ephemeropteran nymphs, trichopteran larvae, mollusks, and fish eggs. The benthos composition differed among sites. Positive values for Ivlev's electivity index were found for malacostracans and ephemeropteran nymphs at all four upstream sites and for dipteran larvae at one upstream site; mollusks were generally negatively selected at one upstream site. At the three sites where the same sampling strategy was used, food preference differed as a function of site and month. Within some site × month combinations, preference also varied with fish length. Our results (1) confirm that juvenile lake sturgeon are generalists and opportunistic benthic feeders, (2) reveal that diet composition is only partly determined by benthos availability, and (3) suggest that there is positive selection for drifting prey. Within the study area, lake sturgeon aggregate locally, but the presence of juveniles in these specific areas cannot be fully explained by their food habits.
Impact of common ragweed (Ambrosia artemisiifolia) aggregation on economic thresholds in soybean
Authors: Cowbrough Michael J. , Brown Ralph B. , Tardif François J.
Published: July 2006

One approach to site-specific weed control is to map weeds within a field and then divide the field area into smaller grid units. The decision to apply a herbicide to individual grid units, or decision units, is made by using yield loss models to establish an economic threshold level. However, decision units often contain weed populations with aggregated distributions. Many yield loss models have not considered this because experiments dealing with weed–crop competition typically assume uniform weed distributions. Therefore, these models may overestimate yield losses. Field experiments conducted in 1999 and 2000 compared the effects of common ragweed having a uniform distribution vs. an aggregated distribution on soybean seed yield, moisture content, and dockage. Field experiment data were used to calculate and compare economic thresholds for both distributions. Economic thresholds that considered drying costs and dockage also were compared. There was no significant difference inIparameters (yield loss as density approaches zero) between the two ragweed distributions in either year. Seed moisture content and dockage increased with increasing common ragweed densities, but increases were not significant at the break-even yield loss level. Economic threshold values were similar for both distributions with differences between aggregated and uniform of 0.14 and 0.01 plants m−2in 1999 and 2000, respectively. The economic threshold values were reduced by 0.01 to 0.06 plants m−2when drying costs and dockage were considered.
Kudzu (Pueraria montana) community responses to herbicides, burning, and high-density loblolly pine
Authors: Harrington Timothy B. , Rader-Dixon Laura T. , Taylor John W.
Published: July 2006

Kudzu is an aggressive, nonnative vine that currently dominates an estimated 810,000 ha of mesic forest communities in the eastern United States. To test an integrated method of weed control, abundances of kudzu and other plant species were compared during 4 yr after six herbicide treatments (clopyralid, triclopyr, metsulfuron, picloram + 2,4-D, tebuthiuron, and a nonsprayed check), in which loblolly pines were planted at three densities (0, 1, and 4 seedlings m−2) to induce competition and potentially delay kudzu recovery. This split-plot design was replicated on each of the four kudzu-dominated sites near Aiken, SC. Relative light intensity (RLI) and soil water content (SWC) were measured periodically to identify mechanisms of interference among plant species. Two years after treatment (1999), crown coverage of kudzu averaged < 2% in herbicide plots compared with 93% in the nonsprayed check, and these differences were maintained through 2001, except in clopyralid plots where kudzu cover increased to 15%. In 2001, pine interference was associated with 33, 56, and 67% reductions in biomass of kudzu, blackberry, and herbaceous vegetation, respectively. RLI in kudzu-dominated plots (4 to 15% of full sun) generally was less than half that of herbicide-treated plots. SWC was greatest in tebuthiuron plots, where total vegetation cover averaged 26% compared with 77 to 111% in other plots. None of the treatments eradicated kudzu, but combinations of herbicides and induced pine competition delayed its recovery.
Corn leaf architecture as a tool for weed management in two corn production systems
Authors: Sankula Sujatha , VanGessel Mark J. , Mulford Ronald R.
Published: July 2006

Research in irrigated and nonirrigated corn production systems was conducted to evaluate the effect of leaf architecture of corn hybrids on weed management. The corn hybrids used in each study were ‘Pioneer 3394’ (upright leaf) and ‘Pioneer 3260’ (horizontal leaf). In the irrigated study, residual weed control treatments included two rates of prepackaged mixtures of metolachlor plus atrazine, encapsulated acetochlor plus atrazine, nonencapsulated acetochlor plus atrazine, or a tank mixture of simazine and metolachlor plus atrazine. In the irrigated experiments, horizontal leaf architecture reduced weed density (all three sites in 1 of 2 yr), weed biomass (five of six sites), solar radiation reaching the ground (all six sites), and weed seed production (one site each year) compared with upright leaf architecture. Weed density and weed biomass did not differ between herbicide rates or acetochlor formulation at any site. Corn hybrid was significant for yield at only one site. Reduced weed biomass did not translate into yield differences. The nonirrigated study evaluated two factors at four sites over 2 yr: leaf architecture (upright or horizontal leaf) and weed management program (preemergence residual and postemergence no residual) at two application rates. Neither weed density nor weed biomass was reduced because of corn leaf architecture or herbicide rates in the nonirrigated study. No interaction was detected in either irrigated or nonirrigated studies between leaf architecture and herbicide treatments, indicating that these factors are independent of one another. On the basis of these studies, it appears that horizontal leaf architecture of corn hybrids can assist in integrated weed management in irrigated corn production but may not be beneficial when corn is grown under drought-prone conditions.
Weed management with CGA-362622 in transgenic and nontransgenic cotton
Authors: Porterfield Dunk , Wilcut John W. , Wells Jerry W. , Clewis Scott B.
Published: July 2006

Field studies conducted at three locations in North Carolina in 1998 and 1999 evaluated crop tolerance, weed control, and yield with CGA-362622 alone and in combination with various weed management systems in transgenic and nontransgenic cotton systems. The herbicide systems used bromoxynil, CGA-362622, glyphosate, and pyrithiobac applied alone early postemergence (EPOST) or mixtures of CGA-362622 plus bromoxynil, glyphosate, or pyrithiobac applied EPOST. Trifluralin preplant incorporated followed by (fb) fluometuron preemergence (PRE) alone or fb a late POST–directed (LAYBY) treatment of prometryn plus MSMA controlled all the weed species present less than 90%. Herbicide systems that included soil-applied and LAYBY herbicides plus glyphosate EPOST or mixtures of CGA-362622 EPOST plus bromoxynil, glyphosate, or pyrithiobac controlled broadleaf signalgrass, entireleaf morningglory, large crabgrass, Palmer amaranth, prickly sida, sicklepod, and smooth pigweed at least 90%. Only cotton treated with these herbicide systems yielded equivalent to the weed-free check for each cultivar. Bromoxynil systems did not control Palmer amaranth and sicklepod, pyrithiobac systems did not control sicklepod, and CGA-362622 systems did not control prickly sida.
Integration of cover crops with postemergence herbicides in no-till corn and soybean
Authors: Gallagher Robert S. , Cardina John , Loux Mark
Published: July 2006

The integration of cover crops with selected postemergence herbicides was evaluated on the basis of weed control and grain yields in no-till soybean and corn. Soybean was planted into wheat residue, whereas corn was planted into hairy vetch residue. Full, half, and quarter rates and sequential herbicide applications were made. The wheat cover crop did not increase weed suppression but increased soybean grain yields. Half rates of thifensulfuron plus quizalofop-P as single or split applications were as effective as full rates in reducing weed weight in soybean. Soybean grain yields were similar in the half- and full-rate treatments in 1994, but yield was highest in the full-rate treatment in 1995. The hairy vetch cover crop did not increase weed suppression but lowered corn stands and grain yields in 1995 and enhanced corn grain yields in 1996. Full, half, and quarter rates (1996 only) of nicosulfuron plus primisulfuron were equally effective in reducing weed weight. Corn grain yields were similar at all herbicide rates in 1995 but were inversely related to herbicide rate in 1996. Split herbicide applications did not improve weed suppression over single applications of the same herbicide rate in either crop. Results indicate that cover crops can improve crop productivity and reduced rates of environmentally benign herbicides can minimize the herbicide requirements in no-till corn and soybean.
Predicting the potential invasive distributions of four alien plant species in North America
Authors: Peterson A. Townsend , Papes Monica , Kluza Daniel A.
Published: July 2006

Ecological niche modeling, a new methodology for predicting the geographic course of species' invasions, was tested based on four invasive plant species (garlic mustard, sericea lespedeza, Russian olive, and hydrilla) in North America. Models of ecological niches and geographic distributions on native distributional areas (Europe and Asia) were highly statistically significant. Projections for each species to North America—effectively predictions of invasive potential—were highly coincident with areas of known invasions. Hence, in each case, the geographic invasive potential was well summarized in a predictive sense; this methodology holds promise for development of control and eradication strategies and for risk assessment for species' invasions.
Annual bluegrass (Poa annua) populations exhibit variation in germination response to temperature, photoperiod, and fenarimol
Authors: McElroy J. Scott , Walker Robert H. , Wehtje Glenn R. , van Santen Edzard
Published: July 2006

Laboratory studies were conducted to evaluate variation in germination response of eight annual bluegrass ecotypes (‘Augusta 4’, ‘Augusta 8’, ‘Augusta 14’, ‘Augusta 17’, ‘Auburn’, ‘Birmingham’, ‘Columbia’, and ‘Purchased’) to photoperiod, temperature, and fenarimol, a fungicide–herbicide used for preemergence annual bluegrass. Seed collected from greenhouse-grown plants and stored for > 2 mo were evaluated under 18 environments (three day and night temperatures by six day and night durations). There was a significant ecotype by environment interaction affecting annual bluegrass germination. High temperature markedly restricted germination, with only the Birmingham ecotype exceeding 20% germination at day and night temperatures of 39 and 29 C, respectively. Maximum germination of all ecotypes was observed at a day and night temperature of 19 and 10 C, respectively. Maximum germination for a specific photoperiod was not consistent across ecotypes; however, all ecotypes germinated to some degree in complete darkness, which indicates that maintaining a dense turf canopy to eliminate annual bluegrass germination may not be completely effective. Ecotypes did not differ with respect to root length response to fenarimol but did vary with respect to shoot length response. Purchased and Columbia shoot growth were the most tolerant to increasing fenarimol concentrations. This information will be used to develop improved management strategies for annual bluegrass.
Calibration and validation of a common lambsquarters (Chenopodium album) seedling emergence model
Authors: Leblanc Maryse L. , Cloutier Daniel C. , Stewart Katrine A. , Hamel Chantal
Published: July 2006

Studies were conducted to calibrate and validate a mathematical model previously developed to predict common lambsquarters seedling emergence at different corn seedbed preparation times. The model was calibrated for different types of soil by adjusting the base temperature of common lambsquarters seedling emergence to the soil texture. A relationship was established with the sand mineral fraction of the soil and was integrated into the model. The calibrated model provided a good fit of the field data and was accurate in predicting cumulative weed emergence in different soil types. The validation was done using data collected independently at a site located 80 km from the original experimental area. There were no differences between observed and predicted values. The accuracy of the model is very satisfactory because the emergence of common lambsquarters populations was accurately predicted at the 95% probability level. This model is one of the first to take into consideration seedbed preparation time and soil texture. This common lambsquarters emergence model could be adapted to model other weed species whose emergence is limited by low spring temperature.
Postdispersal predation of giant ragweed (Ambrosia trifida) seed in no-tillage corn
Authors: Harrison S. Kent , Regnier Emilie E. , Schmoll Jerron T.
Published: July 2006

Giant ragweed seeds have high nutritional value, consisting of 47% crude protein and 38% crude fat, and may be an important food source for rodent and invertebrate populations in agricultural and early successional ecosystems. We investigated temporal patterns of postdispersal giant ragweed seed predation on the soil surface of a no-tillage cornfield as affected by involucre (seed dispersal unit) size and presence or absence of crop residue. Cage exclusion experiments indicated that rodents and invertebrates were the principal predators of giant ragweed seed, and total predation of involucres over a 12-mo period beginning in November was 88%. Rodents were the greatest predators of giant ragweed involucres during fall and winter, and cumulative predation by February 1 in treatments with rodent access ranged from 39 to 43%. In contrast, giant ragweed involucre predation by invertebrates occurred mainly from May 1 to November 1. When rodent access to involucres was prevented, total involucre predation by invertebrates over a 12-mo period ranged from 57 to 78%. Rodents showed an initial preference for large involucres (> 4.8-mm diameter), and invertebrates preferred small involucres (< 4.8-mm diameter). Involucres covered with corn plant residue underwent less predation by rodents from November to February than uncovered involucres, but residue cover had no effect on seed predation by invertebrates. In a laboratory feeding trial, the carabidHarpalus pensylvanicuspreferred seed of smooth pigweed and yellow foxtail to giant ragweed seed, suggesting that giant ragweed seed is an incidental rather than a preferred food source for some carabids. Because giant ragweed exhibits relatively low fecundity and short seed bank persistence, results of this study suggest that postdispersal predation may directly reduce giant ragweed recruitment the next year by reducing new seed bank inputs. However, seed losses from predation alone may be insufficient to maintain giant ragweed populations below economic threshold levels in no-tillage cornfields.
Root-knot nematodes affect annual and perennial weed interactions with chile pepper
Authors: Schroeder Jill , Thomas Stephen H. , Murray Leigh W.
Published: July 2006

A field microplot experiment was conducted in 1996 and 1997 to determine the influence of root-knot nematodes on intra- and interspecific interactions between chile pepper (chile) and spurred anoda and between chile and yellow or purple nutsedge (or both) using a substitution design. An additional objective was to determine the influence of London rocket, a winter annual and host plant for root-knot nematodes, on the inter- and intraspecific interactions between chile and spurred anoda. Twelve plant combinations were planted into paired 76-cm-diam microplots at a density of 24 plants per microplot each year. Each pair of microplots had one root-knot nematode–infested and one uninfested plot. One randomly selected plant pair or triplet from each plot was destructively sampled in June, July, August, and September each year. Data included leaf area, plant dry weights (leaf, stem, root or root plus rhizome, chile fruit, and nutsedge tuber), and nematode egg production from the belowground biomass of the different plant species within a 2,355-cm3sampled soil volume. Chile hosted the highest population of root-knot nematodes, followed by spurred anoda, purple nutsedge, and yellow nutsedge. Few root-knot nematode eggs were recovered from London rocket before incorporation into the microplots each spring. Root-knot nematode populations were higher in 1997 and, as a result, more interactions between nematodes and plant combinations were observed for chile. Spurred anoda and root-knot nematodes reduced chile shoot and root weights to levels not significantly different from zero in 1997. Yellow and purple nutsedge shoots, except for those from the original tuber, were removed throughout the season, and these species interfered less with chile. Spurred anoda was not affected by interspecific interference. Few interactions were observed between the spurred anoda plant combinations and root-knot nematodes. In June 1996, low populations of root-knot nematodes (< 4,000 eggs per gram of root) stimulated spurred anoda growth, but higher populations in June 1997 (> 30,000 eggs per gram of root) reduced spurred anoda growth. Prior presence of London rocket had little consistent influence on spurred anoda or chile. Yellow and purple nutsedge growth variables were affected by interference from chile and the other nutsedge species. Tuber number and tuber weight were higher when plants were infected with root-knot nematodes, particularly early in the season. The enhanced tuber production may increase early-season interference from nutsedge species under production conditions. The results suggest that the presence of root-knot nematodes influences plant interference, but the effect is species specific. Annual plants are affected differently compared with perennial nutsedges, possibly because of the continuous association between the perennials and the parasite.
Conventional- and conservation-tillage systems influence emergence periodicity of annual weed species in canola
Authors: Bullied W. John , Marginet Anastasia M. , Van Acker Rene C.
Published: July 2006

Variation in spring emergence periodicity (both before and after crop seeding) of summer annual weeds is a potentially exploitable attribute that may be applied to weed management in canola. Tillage intensity, which is decreasing in the Great Plains of North America, may influence emergence periodicity of summer annual weeds. Emergence periodicity of common lambsquarters, field pennycress, green foxtail, redroot pigweed, wild buckwheat, wild mustard, and wild oat were monitored during the spring of 2000 in 17 producers' canola fields across southern Manitoba, Canada. The fields represented a region of approximately 2 million ha and included a broad range of soil types, agronomic practices, environmental conditions, and seedbank distributions. Fields were grouped into one of two broad tillage classifications (conventional or conservation). For most species, except redroot pigweed and wild mustard, conservation tillage promoted earlier emergence than conventional tillage in terms of both thermal and chronological time. The differences were significant even though there was only a limited range of tillage intensity for the two tillage classes within this region. Onset of canola crop emergence preceded that of all but one weed species in the conservation-tillage fields and five weed species in the conventional-tillage fields. This suggests that canola seeded in conservation- vs. conventional-tillage systems may have a competitive advantage by way of an earlier relative time of crop emergence. The influence of tillage system on weed emergence periodicity is likely due to the influence of tillage on the vertical origin of weed seedling recruitment because measurements of soil temperature and soil moisture did not help to fully explain the differences in emergence periodicity between tillage systems. The results from this study will facilitate weed control timing decisions in canola and provide validation data for weed emergence models.
Temperature effects on germination and growth of redroot pigweed (Amaranthus retroflexus), Palmer amaranth (A. palmeri), and common waterhemp (A. rudis)
Authors: Guo Peiguo , Al-Khatib Kassim
Published: July 2006

Experiments were conducted to determine the effects of temperature on seed germination and growth of redroot pigweed, Palmer amaranth, and common waterhemp. At 15/10 C day and night temperature, respectively, no seed germination was observed in any species. Seed germination increased gradually as temperature increased. Germination peaked at 25/20 C in common waterhemp and at 35/30 C in redroot pigweed and Palmer amaranth. Seed germination of all three species declined when temperatures increased above 35/30 C. All three species produced less biomass at 15/10 C than at 25/20 C and 35/25 C. Redroot pigweed and common waterhemp biomass were similar at 15/10 C and higher than that of Palmer amaranth. However, Palmer amaranth produced more biomass than redroot pigweed and common waterhemp at 25/20 and 35/30 C. At 45/40 C, redroot pigweed, common waterhemp, and Palmer amaranth plants died 8, 9, and 25 d after initiation of heat treatment, respectively. The largest root volume among the three species was in Palmer amaranth grown at 35/30 C, whereas the smallest root volume was produced by Palmer amaranth grown at 15/10 C. Potential quantum efficiency (Fv/Fmax) of Palmer amaranth was higher than that of redroot pigweed and common waterhemp at higher temperature. The greater growth of Palmer amaranth at higher temperatures may be attributed in part to its extensive root growth and greater thermostability of its photosynthetic apparatus.
Cropping system effects on giant foxtail (Setaria faberi) demography: I. Green manure and tillage timing
Authors: Davis Adam S. , Liebman Matt
Published: July 2006

Manipulation of cropping systems to improve weed management requires a better understanding of how crop- and soil-related factors affect weed life cycles. Our objective was to assess the impacts of timing of primary tillage and use of legume green manure on giant foxtail demography and soil properties. We measured giant foxtail seed survival and dormancy, seedling emergence and survival, and fecundity, in addition to soil phytotoxicity, chemical properties affecting soil fertility and soil water, in the transition between the wheat and corn phases of a wheat–corn–soybean crop sequence. Postdispersal predation of giant foxtail seeds was measured in all three phases of the crop sequence. Wheat was grown either as a sole crop (W) or underseeded with red clover (R), and residues from this phase were rototilled either in the fall (FT) or in spring (ST). There were strong interactions between Red clover and Tillage timing in their effects on giant foxtail recruitment and fecundity in corn. Giant foxtail seedling emergence was 30% lower, and time to 50% emergence was more than 1 wk later, in the ST/R treatment than in the ST/W, FT/W, and FT/R treatments, which did not differ. However, fecundity of giant foxtail was 200% greater in the ST/R treatment than in the other three treatments because of suppressed early corn growth. The net effect of the ST/R treatment on giant foxtail demography in corn was to greatly increase inputs to the seedbank compared with the ST/W, FT/W, and FT/R treatments. Giant foxtail demography in the wheat phase was also affected by Red clover. There was a 200% increase in daily rates of postdispersal seed predation in the wheat phase of the R treatment compared with the W treatment. High-seed predation in the wheat phase and low fecundity in the corn phase of the FT/R treatment suggest that population growth rate of giant foxtail will be lower in this treatment than in the other treatments. The degree of soil phytotoxicity from red clover residues, the changes in the amount of interference from the corn crop early in the growing season, and the differential suitability of crop residues in the different rotations as habitat for seed predators all contributed to changes in giant foxtail demography. Understanding the effects of cropping system characteristics on entire weed life cycles will facilitate the design of integrated suites of complementary weed management tactics.
Effects of shading on common waterhemp (Amaranthus rudis) growth and development
Authors: Steckel Lawrence E. , Sprague Christy L. , Hager Aaron G. , Simmons F. William , Bollero German A.
Published: July 2006

Common waterhemp is a significant weed problem in Midwestern cropping systems partly because of its potential for multiple emergence events during the growing season. The effects of shade and time of emergence on this weed have not been characterized. In the field, common waterhemp vegetative and reproductive growth were evaluated under different irradiance levels at two emergence times. In full sunlight a common waterhemp plant emerging in late May produced 720 g of biomass and over one million seeds, and a plant emerging in late June produced 350 g of biomass and over 730,000 seeds. Plant biomass and seed production were lower as irradiance levels were decreased to 40, 68, and 99% shade. Mortality was high for common waterhemp grown in 99% shade; however, surviving plants produced some viable seed. Common waterhemp plants grown under reduced irradiance had higher leaf area ratios and lower relative growth rates.
Understanding mechanisms of reduced annual weed emergence in alfalfa
Authors: Huarte H. R. , Arnold R. L Benech
Published: July 2006

Field experiments were carried out at the Facultad de Agronomía, Universidad de Buenos Aires, Argentina (34°25′S, 58°25′W), to evaluate the possibility of reducing weed seedling emergence through the use of alfalfa cultivars with low levels of winter dormancy and by increasing plant density from 200 to 400 plants m−2. It was hypothesized that these treatments would alter the temperature regime and the red (R)–far-red (FR) ratio of radiation to which seeds were exposed. Responses to management treatments were recorded for bull thistle, cotton thistle, plumeless thistle, tall rocket, mustard, curly dock, and pigweed. During the alfalfa establishment year, pigweed and curly dock emergence was reduced by the nondormant cultivar established at high density. This reduction disappeared when soil beneath the canopy was fitted with heaters that mimicked bare-soil temperatures. Crop canopy presence during the establishment year was not effective in reducing mustard, cotton thistle, bull thistle, plumeless thistle, and tall rocket emergence. During the second and third years after crop establishment, the canopy of the nondormant alfalfa cultivar was effective in reducing germination of weed seeds placed on the soil surface during fall and winter. In contrast, the winter-dormant cultivar allowed the establishment of weeds during the winter period. These reductions in weed emergence were associated with a modification in the R–FR ratio perceived by the seeds located at the soil surface and could largely be removed by using FR filters to increase the R–FR ratio. These results suggest that the selection of a nondormant cultivar combined with an increase in plant density could effectively reduce weed populations in alfalfa.
Duration of yellow nutsedge (Cyperus esculentus) competitiveness after herbicide treatment
Authors: Ferrell Jason A. , Earl Hugh J. , Vencill William K.
Published: July 2006

Experiments were initiated to determine the amount of time required for postemergence herbicides to render yellow nutsedge physiologically noncompetitive. The rate of net CO2assimilation (AN) was chosen as the response variable to describe competitiveness. Specifically, the time required after herbicide treatment forANto drop to 50% of that of the untreated control (AN50) was determined.AN50values for halosulfuron, imazapic, glyphosate, and MSMA were 1.6, 2.1, 3.2, and 3.3 d, respectively. AnAN50value was not calculated for bentazon becauseANrapidly decreased below 50% but recovered to > 50% by 9 d after treatment (DAT). Stomatal conductance to water vapor (gs) declined similarly withANover time for halosulfuron, imazapic, and glyphosate treatments. However,gsof MSMA-treated plants was near 95% of the untreated control, whereasANdeclined to 35% 11 DAT. At 11 DAT, all aboveground biomass was removed, and plants were returned to the greenhouse, and regrowth was determined after an additional 14 d. Yellow nutsedge regrowth for halosulfuron, imazapic, glyphosate, and MSMA was below 5% of the untreated control and was not statistically different. However, regrowth from bentazon was 44% of the control. Therefore, bentazon was the least effective herbicide tested, whereas halosulfuron and imazapic were most effective for yellow nutsedge control.
Nitrogen management will influence threshold values of green foxtail (Setaria viridis) in corn
Authors: Cathcart R. Jason , Swanton Clarence J.
Published: July 2006

Environmental legislation may impose limitations on the quantity of nitrogen (N) used in corn production on the basis of soil type and ground water flow. If N rates are reduced, this might influence the relative competitiveness of weed species. Therefore, the objectives of this research were to develop a surface response model to provide estimations of the effect of differing N rates on threshold values of green foxtail in corn and to use this model as a theoretical framework for hypothesis testing. Field experiments were conducted from 1999 to 2001 to examine the interaction of N rate and green foxtail density on corn grain yield. The experiment was designed as a two-factor factorial with N levels ranging from 0 to 200 kg N ha−1and targeted green foxtail densities ranging from 0 to 300 green foxtail plants m−2. The addition of up to 200 kg N ha−1increased corn grain yield in both weed-free and weedy treatments. Corn yield loss attributed to green foxtail ranged from 35 to 40% at 0 kg N ha−1to 12 to 17% at 200 kg N ha−1. Ridge analysis of the response surfaces indicated that optimal corn grain yield could be achieved at derived values of 131 to 138 kg N ha−1while maintaining a green foxtail density of 8 to 9 green foxtail plants m−2on a sandy soil with less than 2% organic matter. The analyses of simulation results led to the generation of hypotheses of practical relevance to N management. On the basis of the generated hypotheses, a legislated reduction in N or an increase in the cost of N fertilizer would result in a lower threshold value for green foxtail in corn. If legislation were to ban the use of all herbicides in corn production, higher N rates or an increase in mechanical weed control measures would be required to offset yield losses caused by green foxtail. The human health and environmental consequences of such legislation would be significant.
WeedSOFT®: a weed management decision support system
Authors: Neeser Christophe , Dille J. Anita , Krishnan Gopal , Mortensen David A. , Rawlinson Jeffery T. , Martin Alex R. , Bills Lynn B.
Published: July 2006

WeedSOFT® is a decision support system that was developed to help farmers and consultants in Nebraska with the selection of optimal weed management strategies. WeedSOFT® evolved from HERB, a bioeconomic model for soybean that was developed in North Carolina. The program is composed of four independent modules, namely, ADVISOR, EnviroFX, MapVIEW, and WeedVIEW. ADVISOR helps the user select a treatment based on maximum yield or maximum net gain. EnviroFX and MapVIEW provide environmentally relevant herbicide information and county soil maps that indicate vulnerability to groundwater contamination. WeedVIEW is a visual library of color images and line drawings of 46 common weed species. Over 500 farmers and consultants in Nebraska and adjacent states use WeedSOFT®. As a result of the current regionalization effort, the user base is expected to increase rapidly during the next 2 or 3 yr. This article explains the algorithms implemented in the current version of WeedSOFT®.
Cover crop, tillage, and herbicide effects on weeds, soil properties, microbial populations, and soybean yield
Authors: Reddy Krishna N. , Zablotowicz Robert M. , Locke Martin A. , Koger Clifford H.
Published: July 2006

A field study was conducted during 1997 to 2001 on a Dundee silt loam soil at Stoneville, MS, to examine the effects of rye and crimson clover residues on weeds, soil properties, soil microbial populations, and soybean yield in conventional tillage (CT) and no-tillage (NT) systems with preemergence (PRE)-only, postemergence (POST)-only, and PRE plus POST herbicide programs. Rye and crimson clover were planted in October, desiccated in April, and tilled (CT plots only) before planting soybean. Both cover-crop residues reduced density of barnyardgrass, broadleaf signalgrass, browntop millet, entireleaf morningglory, and hyssop spurge but did not affect yellow nutsedge at 7 wk after soybean planting (WAP) in the absence of herbicides. Densities of these weed species were generally lower with PRE-only, POST-only, and PRE plus POST applications than with no-herbicide treatment. Total weed dry biomass was lower when comparing CT (1,570 kg ha−1) with NT (1,970 kg ha−1), rye (1,520 kg ha−1) with crimson clover (2,050 kg ha−1), and PRE plus POST (640 kg ha−1) with PRE-only (1,870 kg ha−1) or POST-only (1,130 kg ha−1) treatments at 7 WAP. Soils with crimson clover had higher organic matter, NO3–N, SO4–S, and Mn, and lower pH compared with rye and no–cover crop soils. Total fungi and bacterial populations and fluorescein diacetate hydrolytic activity were higher in soil with crimson clover, followed by rye and no cover crop. Soybean yields were similar between CT (1,830 kg ha−1) and NT (1,960 kg ha−1), no cover crop (2,010 kg ha−1) and rye (1,900 kg ha−1), and rye and crimson clover (1,790 kg ha−1), but they were higher in PRE plus POST (2,260 kg ha−1) than in PRE-only (1,890 kg ha−1) or POST-only (1,970 kg ha−1) treatments.
Secondary seed dormancy prolongs persistence of volunteer canola in western Canada
Authors: Gulden Robert H. , Shirtliffe Steven J. , Gordon Thomas A.
Published: July 2006

In western Canada, little is known about the seedbank ecology of volunteer canola. Therefore, integrated recommendations for the management of this weed are limited. In this study, we investigated the seedbank persistence and seedling recruitment of two spring canola genotype groups with different secondary seed dormancy potentials under contrasting tillage systems. The study was conducted at two locations with different soils in the Mixed Moist Grassland ecoregion of Saskatchewan. A single cohort seedbank was established in 1999 and was followed for 3 yr in successive wheat crops. In a separate laboratory study, the six canola genotypes examined were classified as those with high and those with medium potentials for the development of secondary seed dormancy (HD and MD, respectively). After one, two, and three winters, maximum persistence of 44, 1.4, and 0.2% of the original seedbank was observed among the treatments, respectively. In 2001, HD canola genotypes tended to exhibit 6- to 12-fold greater persistence than MD canola genotypes, indicating lower seedbank mortality in HD canola. Seedling recruitment of HD canola also was higher than MD canola when differences were observed between these genotype groups. Therefore, long-term seedbank persistence of canola can be reduced by growing genotypes with low inherent potential for the development of secondary seed dormancy. The proportion of persisting seeds tended to be higher under conventional tillage than under zero tillage because of lower seedbank mortality, but no clear distinction in seedbank persistence in terms of absolute time could be made between these two tillage systems. Volunteer canola seedling recruitment followed the pattern of a typical summer-annual weed, where seedling emergence was observed only during May and June.
Mechanisms of interference of smooth pigweed (Amaranthus hybridus) and common purslane (Portulaca oleracea) on lettuce as influenced by phosphorus fertility
Authors: Santos Bielinski M. , Dusky Joan A. , Stall William M. , Bewick Thomas A. , Shilling Donn G.
Published: July 2006

Greenhouse studies were conducted to assess the intensity of smooth pigweed and common purslane aboveground interference (AI) and belowground interference (BI) with lettuce and to determine primary mechanisms of interference of each species as affected by P fertility rates. Lettuce was transplanted in mixtures with either smooth pigweed or common purslane according to four partitioning regimes: no interference, full interference, BI, and AI. Soil used was low in P for optimum lettuce yields, therefore P was added at rates of 0, 0.4, and 0.8 grams of P per liter of soil. Shoot and root biomass and plant height were measured for each species, as well as P tissue content. The data obtained indicated that smooth pigweed interfered with lettuce primarily through light interception by its taller canopy. A secondary mechanism of interference was the absorption of P from the soil through luxury consumption, increasing the P tissue content without enhancing smooth pigweed biomass accumulation. In contrast, common purslane competed aggressively with lettuce for P. Because the weed grew taller than lettuce, light interception was a secondary interference factor.
Effect of temperature on the germination of common waterhemp (Amaranthus tuberculatus), giant foxtail (Setaria faberi), and velvetleaf (Abutilon theophrasti)
Authors: Leon Ramon G. , Knapp Allen D. , Owen Micheal D. K.
Published: July 2006

Common waterhemp, giant foxtail, and velvetleaf seed germination in response to temperature was studied with a two-way thermogradient plate. Seeds were maintained under dark and wet conditions at 4 C for 12 wk, and velvetleaf seeds were scarified before the experiments were conducted. The seeds were germinated at 25 different temperature treatments. Minimum and optimum temperatures for velvetleaf germination were approximately 8 and 24 C, respectively. Temperature alternation did not affect the germination of this species. The minimum germination temperature was 10 C for common waterhemp and 14 C for giant foxtail. The optimum germination of giant foxtail occurred at approximately 24 C, but common waterhemp optimum germination was variable depending on temperature alternation. Increased amplitude of the diurnal temperature alternation increased percent germination of these two species, and this was more evident at lower temperatures. In the case of common waterhemp, the temperature required to reach specific germination percentages was reduced by increasing the amplitude of the temperature alternation.