bluuebunny/crossref_metadata_2025 huggingface dataset:
Simulation of Competition for Photosynthetically Active Radiation Between Common Ragweed (Ambrosia artemisiifolia) and Dry Bean (Phaseolus vulgaris)
Authors: Chikoye David , Hunt Leslie A. , Swanton Clarence J.
Published: May 2019

The influence of weeds on crop yield is not only dependent on weed-related factors such as density and time of emergence, but also on environmental and management factors that affect both the weed and crop through time. This study was undertaken to develop the first physiologically based dry bean model that would account for the influence of weed competition. The specific objective was to develop a model that would account for the influence of weed competition on crop yield, and to use this model to test the hypothesis that crop yield losses resulted from competition for photosynthetically active radiation (PAR). To this end, a model that simulated the growth and development of dry bean was developed. The model performed daily calculations and simulated the phenology, leaf area expansion, dry matter production and distribution, and grain yield of dry bean based on weather and management information, but assumed adequate water and nutrients. The model was calibrated without weed competition at two locations and yr, and for these situations, adequately described the growth and development of the crop. Simulations were then run for five common ragweed densities and two times of emergence. Common ragweed leaf area was read into the model from input files and used to simulate weed shading. Shading of the dry bean canopy by common ragweed accounted for about 50 to 70% of the yield losses observed in field studies when weeds emerged with the crop. Weed shading did not account for the yield reduction measured from weeds that emerged at the second trifoliate stage of crop growth. The agreement between model predictions and field studies was consistent with the hypothesis that competition for PAR was a principal factor in weed-crop interaction. The ability to account for differences in weed densities, management, and environmental conditions suggested that modeling was a useful tool for evaluating the interaction among weeds and crops.
Parametric Sequential Sampling Based on Multistage Estimation of the Negative Binomial Parameterk
Authors: Johnson Gregg A. , Mortensen David A. , Young Linda J. , Martin Alex R.
Published: May 2019

An intensive survey of two farmer-managed corn and soybean fields in eastern Nebraska was conducted to investigate parametric sequential sampling of weed seedling populations using a multistage procedure to estimatek, of the negative binomial distribution.kis a nonspatial aggregation parameter related to the variance at a given mean value. Mean weed seedling density ranged from 0.18 to 3.11 plants 0.38 m−2(linear meter of crop row) based on 806 sampling locations. The average value ofk, derived from 200 multistage estimation procedures, ranged from 0.17 to 0.32. A sequential sampling plan was developed with the goal of estimating the mean with a coefficient of variation (CV) of 10, 20, 30, and 40% of the sample mean. A sampling plan was also constructed to estimate the mean within a specified distance H of the true mean (H(x̄)= 0.10, 0.50 and 1.0 plants 0.38 m−2) with 80, 85, and 90% confidence. Estimating mean weed seedling density within a specified CV of the true mean CV(x̄) using parametric sequential sampling techniques was superior to estimating the mean within a specified distance (H(x̄)) of the true mean when considering the frequency of sampling and probability of error, especially at intermediatekvalues. At ak: value of 0.32 and 0.25, the difference between the actual CV(x̄) obtained from sampling and the CV(x̄) specified by the sampler was minimal. However, the accuracy of weed seedling density estimates was reduced with decreasingkvalues below 0.25, especially as the specified CV(x̄) increased.
Littleseed Canarygrass (Phalaris minor) and Short-spiked Canarygrass (Phalaris brachystachys) Interference in Wheat and Barley
Authors: Afentouli Catherine G. , Eleftherohorinos I. G.
Published: May 2019

Field experiments were established in Greece from 1990 to 1993 to study the effect of littleseed and short-spiked canarygrass density on wheat and barley yield, as well as the influence of littleseed canarygrass removal time on wheat yield. Competitive ability of both canarygrass species in wheat was similar, though littleseed canarygrass showed faster growth rate and formed more panicles than short-spiked canarygrass. Grain yield of wheat was not significantly affected by the presence of 76 plants m−2of either canarygrass species, but it was reduced by 36 to 39% by the presence of 304 canarygrass plants m−2. None of the canarygrass species at any density had any effect on grain yield of wheat when cold and dry conditions prevailed during the early stages of growth. Grain yield of barley was not affected by any density of either canarygrass species. Growth and consequently panicle number of both canarygrass species were severely reduced by the interference of barley. The littleseed canarygrass removal time study indicated that emergence of this weed was completed by the middle of February. Grain yield of wheat grown with 150 littleseed canarygrass plants m−2was not affected even when these plants were removed early in April. However, the presence of these canarygrass plants until harvest reduced grain yield of wheat by 23 to 28%.
Environmental Factors Affecting Germination of Tropical Soda Apple (Solanum viarum)
Authors: Akanda Rais U. , Mullahey J. Jeffrey , Shilling Donn G.
Published: May 2019

Laboratory studies were conducted to determine the effect of various factors on germination of tropical soda apple. Tropical soda apple seed were found to be moderately photoblastic with 30% germination occurring in the dark. Germination increased in response to green (545 nm) and red light (650 nm) to 75 and 66%, respectively, indicating phytochrome regulation. No germination occurred in response to blue (450 nm) and far-red light (750 nm). Germination increased from 4 to 64% between 10 to 30 C, but no germination was found at 5 and 40 C. Maximum germination occurred at 30 C. A second degree polynomial (Y= −48.7 + 7.9X – 0.2X2, R2= 0.76) best fit the data. Seed germinated over a broad range of pH (2 to 14) with the highest germination occurring at pH 8 and no germination occurring at pH 2 and 14 (Y = −63.3 + 30.5X – 1.9X2, R2= 0.95). Seed germination declined as osmotic potential increased from 0 to −1.0 MPa (Y = 76.7 – 12.9X + 5.2X2, R2= 0.87). Seedling emergence was maximum from depth of 3 to 6 cm, but no seedling emergence occurred when seed were planted below 12 cm (Y = 10.2 + 17.8X – 1.6X2, R2= 0.93). Optimum germination occurred at a depth of 5.6 cm. Mechanical and sulfuric acid scarification increased the rate of germination but not the overall percentage. Tap water or hot water increased the rate of germination 26% and KNO3, GA3, or ethephon increased it 53%. Tropical soda apple seed germinated in response to variable environmental and edaphic conditions which could allow establishment in diverse ecosystems.
Growth and Development of Wild Poinsettia (Euphorbia heterophylla) Selections in Peanut (Arachis hypogaea)
Authors: Brecke Barry J. , Tobola Piotr
Published: May 2019

Wild poinsettia is a serious weed in several crops, including peanut, grown in the southeastern United States. A study was conducted over 3 yr at Jay, FL, to characterize the growth and development of wild poinsettia grown from seed collected at Plains, GA; Marianna, FL; and Baton Rouge, LA. Seedlings from each selection were transplanted to the field and were grown either alone or in competition with peanut. Observations made throughout the growing season indicated that the Louisiana selection flowered later, grew to a larger size, produced more leaf area and biomass, and caused greater light attenuation and peanut yield reduction than the other two selections. The Georgia selection produced the smallest plants, least leaf area and biomass, and was least competitive with peanut. The Florida selection was intermediate for these parameters. Wild poinsettia dry biomass production was reduced by 78 to 83% when grown with peanut compared with monoculture wild poinsettia.
Reduced Rates of Preemergence and Postemergence Herbicides for Large Crabgrass (Digitaria sanguinalis) and Goosegrass (Eleusine indica) Control in Bermudagrass (Cynodon dactylon)
Authors: Johnson B. Jack
Published: May 2019

Sequential applications of preemergence (PRE) and postemergence (POST) herbicides were applied over a two-year period for large crabgrass and goosegrass control in common bermudagrass. Large crabgrass control was better when prodiamine at 0.3 kg ai ha−1or oryzalin at 0.8 kg ai ha−1were applied in late February, and followed by MSMA at 1.1 kg ai ha−1in June than when prodiamine (0.8 kg ha−1) or oryzalin (2.4 kg ha−1) were applied at recommended rates. Goosegrass control was better when prodiamine was applied at 0.3 kg ha−1followed by MSMA plus metribuzin at 2.2 + 0.1 kg ai ha−1, or when oryzalin was applied at 1.7 kg ha−1followed by MSMA plus metribuzin at 1.1 + 0.1 kg ha−1than when prodiamine was applied at 0.8 kg ha−1or oryzalin was applied at 3.3 kg ha−1. There was no increase in goosegrass control when diclofop was applied in sequence after prodiamine or oryzalin compared to diclofop alone. POST applications of diclofop, MSMA, and MSMA plus metribuzin did not injure common bermudagrass more severely when applied to plots previously treated with prodiamine and oryzalin than with POST herbicides alone.
Modelling the Economics of Controlling Nodding Broomrape (Orobanche cernua) in Sunflower (Helianthus annuus)
Authors: García-Torres L. , Castejón-Muñoz M. , Jurado-Expósito M. , López-Granados F.
Published: May 2019

Field studies were conducted at nine locations in southern Spain during 2 yr to develop models of nodding broomrape competition with sunflower and to establish economic thresholds. At each location, 30 to 35 small plots, each consisting of three sunflower plants, were chosen at random. The infection severity (BIS, no. of emerged broomrapes per sunflower plant) varied from 0 to 35. Plots were harvested at maturity to assess several sunflower and broomrape population variables. The percent sunflower yield reduction averaged over locations due to broomrape was estimated by the equation: % SYR = 1.7 x BIS (r2= 0.92). Crop yield loss per BIS unit increased with the expected yield and was estimated to be about 25, 50, and 75 kg ha−1for yields of 1000, 2000, and 3000 kg ha−1, respectively. A consistent relationship could be established between broomrape-infected sunflower yield, crop and broomrape biomass, and BIS parameters: SSYI= 0.2259 x PoBio/(1 + 0.0687 x BIS) (r2= 0.7820). The BIS economic threshold was about 1.5 and 3.5 for control treatment cost of $ 40 ha−1and potential yields of 2000 and 1000 kg ha−1, respectively.
Potential of Rye (Secale cereale) for Weed Management in Transplant Tomatoes (Lycopersicon esculentum)
Authors: Smeda Reid J. , Weller Stephen C.
Published: May 2019

Weed control in tomato production systems is difficult because few are registered. The use of rye for weed control and its influence on transplant tomato yields was investigated during 1986 and 1987 at two locations in IN to determine if cover crops can provide an alternative weed management technique. ‘Wheeler’ rye was sown in the fall of 1985 and 1986, and mowed or desiccated with glyphosate at various times before planting ‘IND 812'tomatoes. At the time of glyphosate application, rye residues reduced the growth of overwintering weeds by 93% or more compared to bare ground (no cover crop) areas. The time of desiccating rye prior to planting tomatoes affected the extent of weed suppression by rye residues. In 1986, rye treated 4 wk before planting (WBP) tomatoes provided up to 89% suppression of weed growth at 2 wk after planting (WAP) tomatoes, but no measurable weed suppression 5 WAP tomatoes. Rye treated 2 WBP tomatoes provided up to 97% weed suppression up to 5 WAP tomatoes. In 1987, weed suppression varied between locations and differed from 1986. At Lafayette, rye treated 2 and 1 WBP tomatoes provided greater than 81% suppression of weed growth up to 8 WAP tomatoes. Rye mowed and the residues placed into a plot at a known density also reduced weed growth (60%) 8 WAP tomatoes. At Vincennes, however, rye treated 2 and 1 WBP in 1987 did not reduce weed growth later than 4 WAP tomatoes compared to the unweeded, bare ground treatment. The mowed rye residues at Vincennes suppressed weed growth (96%) up to 8 WAP tomatoes. Tomato yield was correlated to weed suppression. In 1986, tomato yield in the rye treated 2 WBP tomatoes was comparable to yield in the bare ground, weeded controls. However, tomato yield in rye plots treated 4 WBP tomatoes was similar to yield in the bare ground, unweeded control. In 1987, tomato yields in all rye plots (mowed, treated 2 and 1 WBP tomatoes) were similar to tomato yields in the bare ground, weeded control at Lafayette. At Vincennes, only the mowed rye treatment yielded comparably to the bare ground, weeded control. In general, rye plots that were weeded yielded similar to or up to 28% more than a bare ground, weeded control. Tomato yields were not reduced by rye residues. Tomato yields in rye residues that provided effective suppression of weed growth (greater than 80%) for a minimum of 4 to 5 WAP tomatoes were comparable to bare ground, weeded controls.
Predisposition of Melaleuca (Melaleuca quinquenervia) to Invasion by the Potential Biological Control Agent Botryosphaeria ribis
Authors: Rayachhetry Min B. , Blakeslee George M. , Center Ted D.
Published: May 2019

Enhancement of the canker causing ability of Botryosphaeria ribis on melaleuca was studied with respect to stress from simulated drought, low temperature, and defoliation treatments. Low xylem water potential was related to increased level of canker development and subsequent tree mortality. Canker development was enhanced by low temperature treatments with alternating exposure to 6 C for 3 d followed by 4 d at 30 (±5) C for 8 wk. Partial defoliation did not affect canker development but complete defoliation of B. ribis-inoculated ramets resulted in tree mortality within 4 wk. Callusing of melaleuca wounds was either reduced or prevented in stressed trees. These observations suggest that stress induced on the tree enhances the tree-killing efficacy of this fungus.
Postemergence AC 263,222 Systems for Weed Control in Peanut (Arachis hypogaea)
Authors: Wilcut John W. , Richburg John S. , Wiley Gerald L. , Walls F. Robert
Published: May 2019

Field studies in 1990 and 1991 at six locations in Georgia and one location in North Carolina evaluated AC 263,222 for weed control, peanut tolerance, and yield. AC 263,222 applied early postemergence at 71 g ai ha−1controlled bristly starbur, coffee senna, common lambsquarters,Ipomoeaspecies, prickly sida, sicklepod, smallflower morningglory, and yellow nutsedge at least 91%. AC 263,222 controlled common cocklebur 77% and Florida beggarweed from 47 to 100%. Crop injury was 4% for AC 263,222 applied once and 12% or less from two applications. Mixtures of bentazon with AC 263,222 did not improve control compared to AC 263,222 alone. Imazethapyr did not improve control of AC 263,222 systems. In several locations, bentazon reduced control of Florida beggarweed with AC 263,222 when applied in a mixture compared to AC 263,222 alone. Weed control from the standard of paraquat plus bentazon applied early postemergence followed by paraquat, bentazon plus 2,4-DB applied POST did not provide the level or spectrum of weed control as AC 263,222 systems.
Economic Evaluation of Field Bindweed (Convolvulus arvensis) Control in a Winter Wheat-Fallow Rotation
Authors: Wiese Allen F. , Salisbury Clay D. , Bean Brent W. , Schoenhals Monty G. , Amosson Steve
Published: May 2019

Field bindweed infests millions of hectares in the Great Plains greatly reducing productivity and value of land. The standard practice for field bindweed control is sweep tillage at 3 wk intervals combined with one or two annual 2,4-D) applications during the 14 mo fallow period in a winter wheat-fallow crop rotation. This was compared to tillage and 2,4-D in conjunction with dicamba or a mixture of picloram+2,4-D applied once during the first October of the first 14 mo fallow period. Also, three no-tillage systems were included using glyphosate+2,4-D at monthly intervals. Two of the treatments were supplemented with dicamba, or picloram+2,4-D as in the sweep tillage system. All treatments controlled field bindweed in two fallow periods and two winter wheat crops, and increased winter wheat yields to about twice the control. Sweep tillage at 3 wk intervals combined with 2,4-D resulted in $36 ha−1profit for an owner-operator compared to $15 ha−1loss with no herbicide or tillage treatment. On average no-tillage lost $35 ha−1. Other treatments, although controlling field bindweed, lost from 35 to $186 ha−1. To determine if long-term benefit after control was achieved, average yields for the area were used to calculate profits using normal farming practices. Profits were 136, 78, and $-50 ha−1, respectively, for sweep tillage and 2,4-D, no-tillage, and the untreated check. In a standard 33:67 owner-tenant rental, profits to the owner for the control period were 90, −33, and $43 ha−1, respectively for tillage and 2,4-D, no-tillage, and untreated check. The tenant lost from $24 to 69 ha−1for the three systems indicating owners must modify rental agreements during a field bindweed control program.
Primisulfuron and Rimsulfuron Degradation in Aqueous Solution and Adsorption in Six Colorado Soils
Authors: Vicari Alberto , Zimdahl Robert L. , Cranmer Brian K. , Dinelli Giovanni
Published: May 2019

Hydrolysis and adsorption of the sulfonylurea herbicides rimsulfuron and primisulfuron were investigated under laboratory conditions. Degradation in aqueous solutions was determined between pH 3 and 8 and between 5 and 35 C. Rimsulfuron degraded faster than primisulfuron. Half-lives at different temperatures at pH 4 ranged from 0.16 to 5.8 d for rimsulfuron and from 0.47 to 16.1 d for primisulfuron. Primisulfuron hydrolysis at 30 C decreased with increasing pH, but rimsulfuron decreased up to pH 7, then increased, suggesting rapid degradation in alkaline conditions. Adsorption, measured in six Colorado soils, was complete within 2 h in all soils. Adsorption isotherms were determined by batch equilibration of 75 to 600 μg L−1. Rimsulfuron was adsorbed in amounts 3.7 to 7 times higher than primisulfuron, with adsorption distribution coefficients (Kd) ranging from 0.1 to to 1.18 for primisulfuron and from 0.71 to 5.1 for rimsulfuron. Adsorption of both herbicides was slightly correlated with soil clay content, and primisulfuron adsorption was also correlated with organic matter content.
Sorption of Bentazon and Degradation Products in Two Mississippi Soils
Authors: Gaston Lewis A. , Locke Martin A. , Wagner Steven C. , Zablotowicz Robert M. , Reddy Krishna N.
Published: May 2019

Bentazon degradation in soil typically proceeds with development of bound residue. Low sorption of bentazon suggests that this residue consists of degradation products; however, there is little data on the sorption behavior of these products. This study was undertaken to determine the sorption of bentazon and the degradation products 2-amino-N-isopropyl benzamide, 2-aminobenzoic acid, andN-methyl bentazon in Dundee silt loam and Sharkey clay, two common agricultural soils of the Mississippi Delta. Greater sorption of bentazon and degradation products in the Sharkey soil was related to finer texture and higher organic C content. Isotherms were nonlinear, with sorption increasing in the order bentazon ≪ 2-amino-N-isopropyl benzamide <N-methyl bentazon. In general, methanol extraction indicated reversible sorption of these compounds. Therefore, it is unlikely that sorption of either 2-amino-N-isopropyl benzamide orN-methyl bentazon contributes to bound residue. In contrast, essentially all of the14C sorbed from radiolabeled 2-aminobenzoic acid solution remained bound after methanol extraction. However, due to degradation of 2-aminobenzoic acid, it was not possible to conclude the extent to which this compound contributed to bound14C. Sorption of14C from 2-aminobenzoic acid exceeded that ofN-methyl bentazon, and at low initial concentrations (≤ 20 μM) was nearly 1000-fold greater than bentazon sorption.
Detection and Dissipation of Isoxaben and Trifluralin in Containerized Plant Nursery Runoff Water
Authors: Wilson C. , Whitwell T. , Riley M. B.
Published: May 2019

Herbicides used in containerized plant production have a potential to move off-site in irrigation runoff water. A granular formulation of isoxaben plus trifluralin was applied to a commercial container plant nursery bed. Herbicides were monitored in irrigation runoff and collection pond water over a period of 60 d. Greatest quantities of both herbicides were lost during the first runoff event following application. Approximately 9.2 and 0.7% of the applied isoxaben and trifluralin, respectively, moved from the application site in runoff water within 5 d after treatment. Herbicide concentrations in runoff water were highest (0.75 μg ml−1 isoxaben and 0.08 (μg ml−1 trifluralin in 1992) during the first 0.25 h following herbicide application. Concentrations in the runoff collection pond climaxed following the first runoff event and decreased to less than 1 ng ml−1 within 60 d after treatment. Photodegradation of isoxaben within the surface 2.5 cm of pond water was greater in light as compared to dark. These studies indicate that isoxaben and trifluralin move from the site of application, but that neither accumulate in the runoff water collection ponds.
Effect of Crop Presence on Persistence of Atrazine, Metribuzin, and Clomazone in Surface Soil
Authors: Gallaher Kent , Mueller Thomas C.
Published: May 2019

Atrazine, metribuzin, and clomazone half-lives averaged over treatments and seasons were approximately 27, 22, and 55 d, respectively. Clomazone dissipation was not affected by the presence or absence of a soybean crop. Atrazine and metribuzin dissipation was not affected by crops in 1992, but was more rapid in no-crop plots than in cropped plots in 1993. The difference may have been the result of higher soil water content with no-crop (a few weeds present) in 1993 than either corn or soybean. Lower soil moisture may have slowed soil microbial activity, thus suppressing atrazine and metribuzin degradation in the 1993 growing season. Few significant correlations were found between herbicide half-life or herbicide concentration and cocklebur growth, although one would expect these to be an index of activity.
Herbicide Effects onRhizoctonia solaniin Vitro and Rhizoctonia Foliar Blight of Soybean (Glycine max)
Authors: Black B. David , Russin John S. , Griffin James L. , Snow Johnnie P.
Published: May 2019

Acifluorfen, alachlor, glufosinate, glyphosate, paraquat, and pendimethalin were evaluated for their effects on mycelial growth and sclerotia/microsclerotia production byRhizoctonia solaniAG-1 IA and IB in culture. All of these herbicides except glufosinate and glyphosate were evaluated for effects on severity of Rhizoctonia foliar blight of soybean in the field. In laboratory studies, all herbicides reduced colony radius ofR. solani.Growth reductions for IB were greater than for IA in the presence of pendimethalin, alachlor, and acifluorfen, but glufosinate reduced growth of IA more than IB. Sclerotia production by both isolates was prevented by paraquat, greatly reduced by glufosinate, but markedly less affected by the other herbicides tested. In field studies, all tested herbicides influenced severity of Rhizoctonia foliar blight when disease pressure was low, but only paraquat reduced severity when disease pressure was high.
Phloem Mobility of Xenobiotics. VII. The Design of Phloem Systemic Pesticides
Authors: Kleier Daniel A. , Hsu Francis C.
Published: May 2019

We have developed a mathematical model for the plant vascular system that enables the prediction of a compound's phloem systemicity as a function of its partition coefficients and acid dissociation constants. The mathematical model can account for the sensitivity of systemicity to plant parameters such as plant size and pH of the phloem sap. This paper reviews this model and demonstrates how it accounts for the phloem systemic properties of most herbicides as well as that of many endogenous substances such as plant hormones. The model also can be used to design phloem systemic pesticides as illustrated for a pronematicide that successfully controls nematodes when applied foliarly to transgenic tobacco plants capable of regenerating the parent nematicide in a root specific fashion.
Thifensulfuron and Imazethapyr Interaction at the ALS Enzyme in Sulfonylurea-Tolerant Soybean (Glycine max)
Authors: Simpson David M. , Stoller Edward W.
Published: May 2019

Greenhouse and laboratory experiments were conducted to determine if the synergistic injury to sulfonylurea-tolerant soybean (STS soybean) caused by applications of thifensulfuron plus imazethapyr involves an interaction between the herbicides at the ALS enzyme. In vitro ALS from STS soybean (Asgrow 3200) was 10 times more tolerant to thifensulfuron than ALS from non-STS soybean (Williams 82). In vivo ALS was 30% of maximum activity 6 HAT in STS soybean treated with 4.4 g ha−1thifensulfuron, but 0% of maximum in similarly treated non-STS soybean. Increasing thifensulfuron from 4.4 to 141 g ha−1did not increase in vivo ALS inhibition in STS soybean, indicating a highly resistant ALS isozyme. Both cultivars responded similarly to imazethapyr in terms of visual injury, in vitro ALS inhibition, and in vivo ALS inhibition. Soybean injury and in vivo ALS inhibition increased with imazethapyr rate in both cultivars. The relationship between imazethapyr inhibition of ALS in vivo and soybean injury was curvilinear. In vitro ALS assays revealed no synergistic interaction between thifensulfuron and imazethapyr at the enzyme level. In vivo ALS activity was reduced to 7 and 10% of controls 24 and 48 HAT by the tank mixture compared to 56 and 84% for thifensulfuron alone and 20 and 28% for imazethapyr alone. These data show that the synergistic increase in soybean injury caused by tank mixing thifensulfuron with imazethapyr results from the cumulative inhibition of ALS, not a synergistic inhibition of the enzyme.
Sampling a Poisonous Plant Population: Quantifying Toxic Alkaloids in Tall Larkspur (Delphinium barbeyi) Leaves
Authors: Manners Gary D. , Pfister James A.
Published: May 2019

Poisonous plants and noxious weeds are often chemically examined to determine concentrations of secondary metabolites which are responsible for their toxic or biological activity. This study examined sample size requirements and sample methods necessary to quantify accurately the concentrations of individual and total toxic alkaloids in two tall larkspur populations. A high performance liquid chromatography analytical method was utilized to determine toxic alkaloid concentrations in all leaves from three individual plant stems and leaves from the remaining stems (remainder) from each of 50 plants in each population. To obtain high precision in quantifying toxic alkaloids in the larkspur populations (within 2.5 to 5% of the population mean, 0.95 confidence), very large numbers of samples (>50–200) were required. However, lower precision (within 10% of the population mean, 0.90–0.95 confidence) required only 20 samples. Similarly, testing parameters relating to toxin concentration in tall larkspur populations within 5 or 10% of the population mean also required hundreds of samples at power levels of 0.95 and α-levels of 0.05. Relaxing power and α-level requirements to 0.80 and 0.1 respectively, reduced sample size to about 30. The means obtained by four different sampling methods were similar (P>0.05). Alkaloid concentrations in leaf samples from single stems were highly correlated to whole-plant leaf (remainder) samples (r2≥0.76), indicating that harvesting leaves from single stems provided representative samples of the entire plant. The results indicate the difficulty in obtaining accurate information about toxins in poisonous plant populations for risk assessment by livestock producers or extension agents and demonstrate the necessity for efficient analytical methodology. Researchers evaluating concentrations of plant compounds in other weeds or toxic plants should consider variability, sampling procedure, and sample size before experiments begin.
Imidazolinone and Sulfonylurea Resistance in a Biotype of Common Waterhemp (Amaranthus rudis)
Authors: Taylor Lovell Sarah , Wax Loyd M. , Horak Michael J. , Peterson Dallas E.
Published: May 2019

The incidence of weed resistance to acetolactate synthase (ALS) inhibiting herbicides has increased in the United States. In 1993, a population of ALS-resistant common waterhemp was discovered after two confirmed applications of an imidazolinone herbicide. Following another imazethapyr application in the glasshouse, the resistant biotype demonstrated 130-fold resistance to imazethapyr at the whole plant level. The concentration of imazethapyr required to inhibit the ALS activity by 50% was 520 times greater for the resistant biotype than the susceptible. Plants also demonstrated cross-resistance to the sulfonylureas, chlorimuron and thifensulfuron, at the whole plant and enzyme levels. This particular discovery is of concern due to the low number of applications of the selection agent (imazaquin 1989, imazethapyr 1992, and imazethapyr in the greenhouse) and the high degree of cross-resistance eliminating several options for weed control.
Smallseed Dodder (Cuscuta planiflora) Gravitropism in Red Light and in Red Plus Far-red
Authors: Orr Gregory L. , Haidar Mustapha A. , Orr Deborah A.
Published: May 2019

White light-grown seedlings of smallseed dodder were cyclically irradiated from above with red light for 4 h followed by red plus far-red for 4 h. Tracings of initially nearly vertical, white light-grown seedlings were made from time-lapsed video images after four cycles of red light followed by red plus far-red. Stems of seedlings cycled into red light were negatively gravitropic and stems of seedlings then cycled into red plus far-red became photoreversibly, positively gravitropic. Observations suggest gravitropic sign reversal in smallseed dodder is regulated by photochrome.
Tillage Effects on Seed Distribution and Common Milkweed (Asclepias syriaca) Establishment
Authors: Yenish Joseph P. , Fry Thomas A. , Durgan Beverly R. , Wyse Donald L.
Published: May 2019

Soil profile distribution of a single simulated seed dispersal event after tillage followed a nonlinear model. Approximately 40% of recovered simulated seed were found within 4 cm of the surface following chisel plowing and disking, and density declined steadily with depth to 20 cm. Moldboard plowing placed 50 to 60% of simulated seed to a depth of 11 to 16 cm. Simulated seed were evenly distributed to 8 cm depth by disking and did not differ regardless of whether plots were chisel or moldboard plowed prior to seed dispersal. More than 90% of seed remained within 2 cm of the surface with no-tillage. Simulated seed distribution was the same after a tillage rotation of chisel plowing, disking, moldboard plowing, and disking regardless if the dispersal event occurred prior to chisel or moldboard plowing. Two years of the tillage rotation and two dispersal events resulted in a distribution pattern greatly influenced by the most recent major tillage of chisel or moldboard plowing. Seedling emergence of common milkweed averaged 80% for seed buried 0.5 to 4 cm deep and emergence was negligible for seed on the surface or buried 7 cm in soil in pots in a growth chamber.
Predicting Yellow Nutsedge (Cyperus esculentus) Emergence Using Degree-day Models
Authors: Wilen Cheryl A. , Holt Jodie S. , McCloskey William B.
Published: May 2019

We examined the relationship between temperature and emergence of yellow nutsedge tubers to generate predictive models for the arid southwestern United States. Field experiments were conducted in California and Arizona to obtain phenological and temperature data needed to generate degree-day models. The effect of air temperature on emergence was tested with available programs using four methods to calculate degree-days (single sine, double sine, single triangle, and double triangle). Separate models were tested for each genotype examined (Arizona source and California source) as no one model was a good predictor of emergence when data were pooled. Results indicate that there is year to year variation in model accuracy but predictions of date of emergence can be made to within 2 d of actual emergence. This information can be used to schedule cultivations to reduce early yellow nutsedge competition in the field.
Herbicide Effects on Ivyleaf Morningglory (Ipomoea hederacea) and Soybean (Glycine max) Growth and Water Relations
Authors: Holloway James C. , Shaw David R.
Published: May 2019

Soybean and ivyleaf morningglory were grown alone and together to quantify water use and growth after treatment with soil-applied chlorimuron plus metribuzin, imazaquin, or no herbicide. Soybean water consumption was 22 ml pot−1day−1or more when grown alone or with another soybean, regardless of herbicide treatment. Ivyleaf morningglory grown alone or with another ivyleaf morningglory consumed ≥ 32 ml water pot−1day−1when no herbicide was applied. Treatment with chlorimuron plus metribuzin or imazaquin reduced ivyleaf morningglory water consumption to ≤ 4 ml pot−1day−1. Water use was reduced with either herbicide when soybean and ivyleaf morningglory were grown together, indicating little or no water consumption by ivyleaf morningglory. Ivyleaf morningglory height, root length, leaf area, and dry matter were reduced by imazaquin or chlorimuron plus metribuzin. Soybean leaf area was also reduced by herbicide treatment or the presence of another plant. Soybean biomass was not reduced in any planting combination, except when two soybean were grown together and treated with imazaquin. Nontreated ivyleaf morningglory partitioned more biomass into the shoots than roots. Ivyleaf morningglory responded to herbicide treatment by partitioning more biomass into roots.
Soybean (Glycine max) Response to Weed Interference and Rhizoctonia Foliar Blight (Rhizoctonia solani)
Authors: Black B. David , Griffin James L. , Russin John S. , Snow Johnnie P.
Published: May 2019

Field studies evaluated response of soybean to Rhizoctonia foliar blight (RFB) disease in combination with varying densities of common cocklebur, hemp sesbania, or johnsongrass. Soybean plants at both V10 and R1 growth stages were not inoculated or inoculated with suspensions containing equal concentrations ofRhizoctonia solaniAG-1 IA and IB mycelia. Intensity of RFB was rated weekly beginning at V1 soybean growth stage, and data were used to determine area under disease progress curves. Intensity of RFB was greater in 1993 than in 1994. When averaged across weed species and weed densities, soybean yield in 1993 was reduced 18% in plots inoculated withR. solanicompared with those not inoculated. Intensity of RFB, however, did not differ between inoculated and noninoculated plots in 1994. Interactions betweenR. solaniand weed density for RFB intensity and yield were not significant either year. Soybean yields in 1994, however, were reduced by hemp sesbania and johnsongrass in inoculated plots. Soybean maturity was delayed both years when hemp sesbania was present.
Competition Between Triazine-Resistant and -Susceptible Common Waterhemp (Amaranthus rudis)
Authors: Anderson Daniel D. , Higley Leon G. , Martin Alex R. , Roeth Fred W.
Published: May 2019

The relative competitiveness of triazine-resistant (TR) and -susceptible (TS) common waterhemp, as a component of fitness, was assessed using TR and TS biotypes collected from the same field in Fillmore County, Nebraska. Competition between biotypes was evaluated under greenhouse conditions using a set of replacement series experiments with five ratios of TR:TS (1:0, 3:1, 1:1, 1:3, and 0:4) and four plant densities (50, 100, 150, and 300 plants m−2). No difference in final individual plant weight between TR and TS plants was observed in the absence of interbiotypic competition at all plant densities examined. Interbiotypic competition was indicated by ANOVA of plant weight and modified relative crowding coefficients (RCC) for plant weight, height, and volume. Replacement series diagrams showed TS plants were more competitive than TR plants, as measured by plant weight at densities of 50, 100, and 150 plants m−2. TS and TR plants were equally competitive at 300 plants m−2. Individual TS plant weight for 50, 100, and 150 plants m−2was greatest at the 3:1 ratio (TR:TS) and decreased as the proportion of susceptible plants increased. Individual TR plant weight for 50, 100, and 150 plants m−2was greatest at the 1:0 ratio and decreased as the TR proportion decreased. Lack of interbiotypic competition at 300 plants m−2and decreasing TS plant weight with increasing ratios suggest intrabiotypic competition. RCC values for volume and height were calculated weekly during the experiment and indicated the competitive advantage of TS plants was constant from transplanting through harvest.
Effect of Herbicides on Ivyleaf Morningglory (Ipomoea hederacea) Interference in Soybean (Glycine max)
Authors: Holloway James C. , Shaw David R.
Published: May 2019

Ivyleaf morningglory weed-free period, weedy period, and density studies were conducted in 1993 and 1994 to determine the effects of soil-applied imazaquin and chlorimuron plus metribuzin on ivyleaf morningglory interference in soybean. A weed-free period of 4 wk was needed to maintain soybean yield equivalent to weed-free season long when herbicides were not used, but treatment with either chlorimuron plus metribuzin or imazaquin maintained yield comparable to weed-free at all intervals. Ivyleaf morningglory biomass was reduced by both herbicides across all weed-free periods. The period nontreated ivyleaf morningglory plants were tolerated without yield loss was only 2 wk, but this interval was extended to 8 wk after treatment with chlorimuron plus metribuzin or imazaquin. Without herbicides, soybean yield was reduced by four ivyleaf morningglory per m of row, but the highest population evaluated in this study (eight per m of row) did not reduce soybean yield after treatment with chlorimuron plus metribuzin or imazaquin. Ivyleaf morningglory biomass was reduced at all densities after treatment with either herbicide.
Effect of Planting Patterns and Inter-row Cultivation on Competition Between Corn (Zea mays) and Late Emerging Weeds
Authors: Murphy Stephen D. , Yakubu Yussif , Weise Stephan F. , Swanton Clarence J.
Published: May 2019

Narrower corn row widths, higher crop densities, and interrow cultivation may be used as part of integrated weed management (IWM). During a three-year study, we tested whether these factors affected corn growth, development and grain yield at final harvest, and weed biomass when weeds were late-emerging (after the three-leaf stage of corn). Increasing corn density from 7 to 10 plants m−2or decreasing row width from 75 to 50 cm significantly increased corn leaf area index (LAI), and reduced photosynthetic photon flux density (PPFD) available for a mixture of weed species located below the corn canopy. Narrower rows and higher corn density significantly reduced biomass of late-emerging weeds. Corn yields increased significantly (10 to 15%) only when narrower rows were used. Intraspecific competition between corn plants in the higher density significantly reduced early corn growth and offset any gain in yield from reduced weed competition. In comparison to plots where late-emerging weeds grew uncontrolled, interrow cultivation did not decrease biomass of late-emerging weeds, hence did not increase corn yield. We recommend using narrower row widths to reduce weed competition and increase corn yield. Increased corn densities had no net yield benefit. Early-season weed management is crucial as the later-emerging weeds were less important in terms of their effect on yield.
Growth and Seed Return of Auxin-Type Herbicide Resistant Wild Mustard (Brassica kaber) in Wheat
Authors: Debreuil Daniel J. , Friesen Lyle F. , Morrison Ian N.
Published: May 2019

The growth and seed return of auxin herbicide resistant (R) wild mustard was compared to that of a susceptible (S) biotype in wheat in the field. In the absence of herbicide, the S biotype accumulated shoot dry matter more quickly than the R biotype throughout most of the growing season. However, in only one of the two years did the S biotype set substantially more seed than the R biotype (3120 versus 2520 seeds plant−1). The recommended dosage of 2,4-D for wild mustard control (420 g ai ha−1) killed all S plants in both years of the study, and severely inhibited growth and seed return of R plants. Shoot dry matter accumulation and seed return of treated R plants were reduced 75 to 90% compared to the untreated control. However, at a density of 20 plants m−2R seed return was still very high; 9000 and 5700 seeds m−2in 1992 and 1993, respectively. The recommended dosage of dicamba (300 g ha−1) did not inhibit the growth and seed return of either S or R wild mustard to the same extent as 2,4-D. Dicamba at 300 g ha−1reduced S shoot dry matter and seed return 80 to 90%, while R shoot dry matter and seed return was reduced 60 to 65%. The results of this study indicate a very high selection pressure for R wild mustard at recommended dosages of 2,4-D. Despite a high selection pressure, and considering the long history of phenoxy herbicide usage on the Prairies, the relatively rare occurrence of phenoxy herbicide resistant weeds implies that the frequency of resistant individuals is very low. From a mathematical model it was determined that the frequency of R wild mustard in an unselected population may be in the order of 10−30.
Effects of Soil Moisture on Observed and Predicted Yellow Nutsedge (Cyperus esculentusL.) Emergence
Authors: Wilen Cheryl A. , Holt Jodie S. , McCloskey William B.
Published: May 2019

Experiments were conducted to examine the effects of low soil moisture on yellow nutsedge emergence in relation to thermal and chronological time and test the ability of thermal models generated previously to predict emergence under water stress. Unsprouted tubers from California and Arizona were planted in pots, buried at field sites in California and Arizona, and subjected to wet or dry treatments. Pots were monitored weekly to determine date of emergence and number of emerged shoots. The California genotype emerged 47 to 61 days after planting (DAP) in the dry treatment and 33 to 49 DAP in the wet treatment, depending on planting site. The range for the Arizona genotype was 51 to 76 DAP in the dry treatment and 43 to 61 DAP in the wet treatment. Days and degree-day intervals to first emergence differed between irrigation treatments and planting sites but interactions were not significant. All models were accurate in predicting emergence dates for genotypes in the wet treatment at the California site, while emergence in Arizona was underestimated by 9 d. Tubers subjected to the dry treatment needed a higher number of accumulated degree-day units before emergence occurred and had fewer emerged shoots as compared to the wet treatment. Degree-day models generated for yellow nutsedge under optimal conditions lack sufficient robustness to be predictive under water stress conditions.
Response of Eastern Black Nightshade (Solanum ptycanthum) to Low Rates of Imazethapyr and Metolachlor
Authors: Ward Katherine I. , Weaver Susan E.
Published: May 2019

Eastern black nightshade is a problem weed in soybeans primarily due to interference with harvesting operations and reductions in crop quality. Field and greenhouse studies were conducted in 1990 and 1991 at Harrow, Ontario, to determine whether sublethal rates of imazethapyr and metolachlor could suppress growth and berry production by eastern black nightshade. In the greenhouse, plants treated with metolachlor PRE at 0.8 kg ai ha−1or imazethapyr POST at 30 g ai ha−1(1/3 to 1/2 the labelled rates) produced significantly fewer berries in the first flower cluster, with fewer seeds per berry, than untreated plants. When a surfactant was added to the imazethapyr, almost all flower buds in the first cluster were aborted. Treated plants recovered from the damage, however, and did not differ significantly from control plants in dry weight or berry production 110 DAP. In the field, application of 50 g ai ha−1imazethapyr POST (2/3 of the lowest labelled rate), with or without a surfactant, resulted in delayed flowering, abortion of most of the flower buds in the first cluster, and greatly reduced growth and total berry production between soybean leaf abscision and harvest. Application of metolachlor + metribuzin PPI in the field at 2/3 of the labelled rate (1.6 + 0.25 kg ai ha−1) was not sufficient to reduce nightshade growth and berry production after soybean leaf abscision. Sublethal rates of imazethapyr and metolachlor did not reduce seed viability in either the greenhouse or the field.
Comparison of Standard and Reduced Production Inputs on Cotton (Gossypium hirsutumL.)
Authors: Monks C. Dale , Patterson Michael G. , Freeman Barry L. , Norris Bobby E.
Published: May 2019

Field trials were conducted from 1991 to 1993 in the northern cotton-producing area of Alabama to evaluate the interaction of various production inputs for pest management and cotton development, maturity, and yield. Two levels of tillage (conventional and no-till), herbicide (1.12 and 2.24 kg ai ha−1fluometuron, preemergence, with post-directed herbicides), insecticide (0.5 and 0.85 kg ai ha−1aldicarb, in-furrow), and fungicide (0.9 kg ai ha−1quintozene plus ethridazole, in-furrow or 0.14 kg ai ha−1metalaxyl, hopper-box) programs were evaluated. The inputs investigated did not interact significantly to change the overall production strategy. Prickly sida required a higher level of herbicide input than did the entireleaf/ivyleaf morningglory complex. Both species were sufficiently controlled using reduced levels of fluometuron without sacrificing yield; however, cultivation was necessary in conventional tillage treatments to maintain control. A postemergence-directed herbicide treatment was also necessary for weed control, regardless of tillage. Decreasing the levels of each input simultaneously did not interact to affect cotton stand, height, early-season thrips counts, cotton maturity, or yield. Cotton was shorter in no-till than conventional plots.