bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Herbicides on Weed Control and Sugarbeet (Beta vulgaris) Yield and Quality
Authors: Dale Trevor M. , Renner Karen A. , Kravchenko Alexandra N.
Published: July 2006

The “micro-rate” application, a POST combination of desmedipham plus phenmedipham at 0.045 + 0.045 kg ai/ha (desphen) or desmedipham plus phenmedipham plus ethofumesate (1:1: 1 ratio) (desphenetho) at 0.09 kg ai/ha plus triflusulfuron at 0.004 kg ai/ha plus clopyralid at 0.026 kg ae/ha plus 1.5% methylated seed oil received registration in 1998 and 2000 in North Dakota and Michigan, respectively. Herbicide rates are reduced by 80%, compared to standard-split applications, and growers typically apply the micro-rate three to five times to very small weeds that are 1 cm or less in height. In standard-split applications, growers make two sequential applications, the first when weeds are 1.5 cm tall and the sequential application usually 10 to 14 d later. Research was conducted in small plots and large grower plots in 2001 and 2002 to determine the effect of PRE herbicides on weed control and sugarbeet injury from micro-rates compared to standard-split POST herbicide applications. Sugarbeet populations were reduced in the cycloate treatment compared to all other PRE and the no-PRE treatment in 2001 and in the S-metolachlor compared to the ethofumesate treatment in 2002. Sugarbeet injury was 6% or less from POST-only treatments in 2001. Control of common lambsquarters and Amaranthus spp. by desphen and desphenetho treatments was similar. Sugarbeet injury in 2002 was 29 to 43% from POST-only treatments. The standard-split of desphenetho was more injurious than the standard-split of desphen. Common lambsquarters control was greater in both the standard-split and micro-rate of desphenetho compared to the standard-split of desphen in 2002. However, sugarbeet populations and recoverable white sucrose per hectare did not differ among POST herbicide treatments in either year. No herbicide program provided 100% control of all weeds in both years. In the seven large production fields, PRE herbicide treatments did not reduce sugarbeet populations or recoverable sucrose per hectare compared to the no-PRE control. Weed control from four POST micro-rate applications only was similar to weed control in instances in which PRE herbicides were applied prior to the POST micro-rate applications.
Desiccant Evaluations: Late-Season Hairy Nightshade (Solanum sarrachoides) Control and Seed Response
Authors: Hutchinson Pamela J.S. , Beutler Brent R. , Hancock Daniel M.
Published: July 2006

Field studies were conducted from 2000 to 2003 to determine the effectiveness of potato desiccants for late-season hairy nightshade control and also their effect on hairy nightshade seed germination. Commercial sulfuric acid at 280 L/ha controlled 94 to 99% of the hairy nightshade 1 wk after treatment (WAT) in all years. Diquat at 560 g/ha and glufosinate-ammonium at 420 g/ha provided at least 93% control 1 WAT in all years except 2003 when control did not exceed 72%. By 3 WAT, hairy nightshade control ranged from 93 to 100% for all treatments, including carfentrazone-ethyl at 56 g/ha, diquat at 420 g/ha, paraquat at 530 g/ha, and sulfuric acid (proprietary process) at 280 L/ha. Treatment of plants with desiccants did not affect germination of hairy nightshade seed, with the exception of a 7% reduction in germination by the higher rate of diquat in 2001 and 2002.
Rapid Assay Evaluation of Plant Response to Protoporphyrinogen Oxidase (Protox)-Inhibiting Herbicides
Authors: Falk Jeanne S. , Al-Khatib Kassim , Peterson Dallas E.
Published: July 2006

Protoporphyrinogen oxidase (protox)-inhibiting herbicides damage cell membranes, resulting in electrolyte leakage. A whole-plant dose-response study and a rapid assay that measured electrolyte leakage was used to determine the response of wild mustard, soybean, and protox inhibitor–susceptible and protox inhibitor–resistant common waterhemp to increasing doses of three protox inhibitors: acifluorfen, fomesafen, and sulfentrazone. For the dose-response study, whole plants were treated with the three protox-inhibitor herbicides. Electroconductivity assay 1 consisted of cutting discs from leaf tissue and submerging them in an incubation medium containing concentrations of acifluorfen, fomesafen, or sulfentrazone. In electroconductivity assay 2, the entire leaf was treated with solutions containing acifluorfen, fomesafen, or sulfentrazone. The whole-plant dose-response study showed increasing visible injury with increasing herbicide rates for all species and all herbicides. The order of visible injury was wild mustard > susceptible common waterhemp > resistant common waterhemp > soybean. In assay 1, electrolyte leakage from leaf discs treated with acifluorfen or fomesafen increased with increasing herbicide concentrations, and was similar for all species. In contrast, electrolyte leakage from leaf discs treated with sulfentrazone did not increase with increasing herbicide concentrations for any species. In assay 2, only wild mustard leaf discs increased in electrolyte leakage with increasing herbicide rates of acifluorfen, fomesafen, and sulfentrazone and followed the regression curves established by the whole-plant dose-response study. However, assay 2 was not able to distinguish between susceptible wild mustard and tolerant soybean, or between susceptible and resistant waterhemp.
Effect of Selected Pesticides on Conidial Germination and Mycelial Growth ofDactylaria higginsii, a Potential Bioherbicide for Purple Nutsedge (Cyperus rotundus)
Authors: Yandoc Camilla B. , Rosskopf E. N. , Pitelli R.L.C.M. , Charudattan R.
Published: July 2006

The suitability of a bioherbicide as a component of an integrated weed management program not only relies on its field efficacy, but also on its compatibility with other pest control measures that may be employed during the cropping season. The effects of selected pesticides applied according to label rates onDactylaria higginsii, a biological control agent for purple nutsedge, were determined using mycelial growth on pesticide-amended potato dextrose agar (PDA) and conidial germination as indicators of pesticide sensitivity. Among the pesticides tested, the herbicides oxyfluorfen and sethoxydim and the fungicides fosetyl-Al and thiophanate methyl inhibitedD. higginsiimycelial growth and reduced or completely inhibited conidial germination; the herbicide diuron, the fungicides metalaxyl and copper hydroxide, and the insecticide cyromazine reduced mycelial growth but did not reduce conidial germination. The miticide dicofol reduced mycelial growth and completely inhibited conidial germination while the herbicide imazapyr had no adverse effect on either the mycelial growth or conidial germination ofD. higginsii.
Preemergence Banded Herbicides Followed by Only One Between-Row Mowing Controls Weeds in Corn
Authors: Donald William W.
Published: July 2006

Research was conducted to determine the minimum number of between-row mowings necessary to control annual weeds, chiefly giant foxtail and common waterhemp, without corn yield loss. Over 2 yr in Missouri, the between-row mowing systems that were evaluated consisted of a 38-cm band of PRE atrazine plus metolachlor at 2.2 plus 2.2 kg ai/ha applied over corn grown in 76-cm rows shortly after planting followed by one, two, or three between-row mowings close to the soil surface. Based on rated total weed control, between-row total weed cover, and corn yield, the weed-free check was statistically indistinguishable from a treatment in which banded PRE herbicide was followed by only one between-row mowing, late, when weeds were relatively large. When mowed once at 52 to 64 days after planting (DAP), giant foxtail and common waterhemp were greater than 85 cm tall. The yield was not increased by mowing earlier or more than once.
Control of Selected Broadleaf Weeds with Glufosinate as Influenced by Insecticide Coapplication
Authors: Miller Donnie K. , Downer Robert G. , Burris E. , Leonard B. Rogers , Williams Bill J.
Published: July 2006

Coapplication of herbicides and insecticides affords growers an opportunity to control multiple pests with one application, given that efficacy is not compromised. Glufosinate was applied at 470 g ai/ha both alone and in combination with the insecticides acephate, acetamiprid, bifenthrin, cyfluthrin, dicrotophos, emamectin benzoate, imidacloprid, indoxacarb, lambda-cyhalothrin, methoxyfenozide, spinosad, or thiamethoxam to determine coapplication effects on control of some of the more common and/or troublesome broadleaf weeds infesting cotton. Hemp sesbania, pitted morningglory, prickly sida, redroot pigweed, and sicklepod were treated at the three- to four- or the seven- to eight-leaf growth stage. When applied at the earlier application timing, glufosinate applied alone provided complete control at 14 d after treatment, and control was unaffected by coapplication with insecticides. When glufosinate application was delayed to the later application timing, visual weed control was unaffected by insecticide coapplication. Fresh-weight reduction from the herbicide applied to larger weeds was negatively impacted by addition of the insecticides dicrotophos and imidacloprid with respect to redroot pigweed and prickly sida, but only in one of two experiments. In most cases, delaying application of glufosinate to larger weeds resulted in reduced control compared to that from a three- to four-leaf application, with the extent of reduction varying by species. Results indicate that when applied according to the herbicide label (three- to four-leaf stage), glufosinate/ insecticide coapplications offer producers the ability to integrate pest management strategies and to limit application costs without sacrificing control of the broadleaf weeds evaluated.
Early Season Mowing Improves the Effectiveness of Chlorsulfuron and Glyphosate for Control of Perennial Pepperweed (Lepidium latifolium)
Authors: Renz Mark J. , Ditomaso Joseph M.
Published: July 2006

Perennial pepperweed is an invasive weed spreading rapidly throughout a wide range of habitats in the western United States. This study was designed to test whether integrating early season mowing with a systemic herbicide application would improve the control of perennial pepperweed. Experiments were conducted within three different environments including high desert, roadside, and floodplain areas. In treatments not mowed, chlorsulfuron at 0.104 kg ai/ha reduced perennial pepperweed biomass and density by 100%, whereas applications of 2,4-D at 2.11 kg ae/ha and glyphosate at 3.33 kg ae/ha were inconsistent and did not provide effective control. Mowing alone did not reduce perennial pepperweed biomass or density the following year, but mowing followed by application of a herbicide treatment to resprouting plants reduced biomass at all three sites compared with nonmowed treatments including herbicides. Among combinations of mowing and herbicides, chlorsulfuron at 0.052 kg/ha reduced perennial pepperweed biomass by >99% at all three sites, and glyphosate at 3.33 kg/ha reduced biomass by ≥80% at two sites 1 yr after applications. The effectiveness of glyphosate at 3.33 kg/ha in combination with mowing provides land managers with a valuable control option for perennial pepperweed in wetland or riparian areas where chlorsulfuron is not registered for use.
Effect of Mowing and Hexazinone Application on Giant Smutgrass (Sporobolus indicusvar.pyramidalis) Control
Authors: Ferrell Jason A. , Mullahey J. Jeffery
Published: July 2006

Giant smutgrass is a perennial, clump-type, grassy weed that commonly infests Florida pastures. Experiments were conducted in 1998 and 1999 in Immokalee, FL, to evaluate multiple mowing treatments in combination with hexazinone applications at 0.56 to 1.7 kg ai/ha, to control giant smutgrass and bahiagrass density. Mowing did not influence giant smutgrass control in 1998 or 1999. Hexazinone application increased giant smutgrass control at all application rates. In 1998, regression analysis determined that hexazinone applied at 0.56 kg/ha provided >90% control of giant smutgrass 182 d after treatment (DAT) and >80% control 321 DAT. Both 1.1 and 1.7 kg/ha of hexazinone provided >90% control for 365 DAT in 1998. In 1999, due in part to excessive rainfall, 0.56 kg/ha provided >80% control for only 48 DAT. It was also concluded that application rates of 0.83 to 0.98 kg/ha hexazinone were the lowest rates that consistently provided 80% or better control over both years. From 0 to 30 DAT, bahiagrass density increased by 17% for the 0.56 kg/ha rate and 2% at the 1.7 kg/ha rate. From 30 to 365 DAT, bahiagrass density increased at 0.04% per day compared with 0.1% per day for 0.56 and 1.7 kg/ha, respectively. Increased bahiagrass injury by the higher application rates of hexazinone was responsible for low levels of bahiagrass growth from 0 to 30 DAT. However, bahiagrass soon recovered from injury, and the higher application rates resulted in a more rapid rate of bahiagrass spread, likely due to less competition of giant smutgrass in plots treated with 1.1 and 1.7 kg/ha rates. These data prove that mowing prior to hexazinone application is an unwarranted expense, and that the 1.1 kg/ha rate provided the most effective and consistent giant smutgrass control with acceptable levels of bahiagrass injury.
Characterization of Waterhemp (Amaranthus tuberculatus) × Smooth Pigweed (A. hybridus) F1Hybrids
Authors: Trucco Federico , Tatum Tatiana , Robertson Kenneth R. , Rayburn A. Lane , Tranel Patrick J.
Published: July 2006

In the state of Illinois, waterhemp and smooth pigweed are among the worst agricultural weeds. Previous research shows high potential for hybridization between these two species. However, the actual occurrence of hybrids in natural settings is still uncertain. Morphological similarity between hybrids and waterhemp makes field surveys of hybrids difficult to conduct. The main purpose of this study was to characterize the morphology of waterhemp × smooth pigweed F1hybrids, emphasizing evaluation of characters that may allow for hybrid discrimination in fieldAmaranthuscommunities. Concurrently, the study characterized hybrid reproductive fitness, chromosome number, and DNA content. To accomplish this, hybrids were obtained from field crosses. A species-specific polymorphism in theALSgene was used to verify hybrid identity. Significant differences (α = 0.05) between hybrids and individuals of the parental species were observed for five staminate and five carpellate characters. Of these, five characters differentiated hybrids from waterhemp. However, clustering analyses using these characters indicated that morphological differences were not reliable enough, by themselves, for unambiguous hybrid identification. Also, hybrid homoploidy (2n= 32) with respect to parental species excluded chromosome counts in hybridity determinations. However, DNA content analysis may be used for such purpose. Hybrids had an average of 1.21 pg of DNA per 2C nucleus, a value intermediate to that of parental species. Hybrids produced 3.3 or 0.7% the seed output of parental and sibling waterhemp individuals, respectively. Percent micropollen in hybrids was 95-times greater than in parental species. Hybrid sterility appears to be the most reliable feature for hybrid discrimination when conducting field surveys. However, molecular and cytogenetic analyses as employed in this study may be desired for ultimate identity corroboration.
Bensulfuron and Halosulfuron Alter Clomazone Activity on Rice (Oryza sativa)
Authors: Webster Eric P. , Mudge Christopher R. , Zhang Wei , Blouin David C.
Published: July 2006

A laboratory study was conducted in 2003 at Louisiana State University in Baton Rouge, LA, to evaluate the interactive effects of bensulfuron or halosulfuron on clomazone in terms of rice foliar bleaching and chlorophyll content. Clomazone was applied alone at 0 and 1.227 μg/ml (672 g/ha) or in combination with bensulfuron at 0.0276 μg ai/ml (42 g ai/ha) or halosulfuron at 0.0345 μg ai/ml (53 g ai/ha) in a hydroponic solution. Bensulfuron and halosulfuron were also applied alone. Rice cultivars evaluated included short-grain ‘Pirogue’, medium-grain ‘Bengal’, and long-grain ‘Cocodrie’. Bensulfuron and halosulfuron, applied in a hydroponic solution, safened medium-grain Bengal, long-grain Cocodrie, and short-grain Pirogue at 21 d after treatment (DAT) from foliar bleaching caused by clomazone. Chlorophyllaandband total chlorophyll content of all three rice cultivars decreased when treated with clomazone treatment. Only chlorophyll content of Cocodrie was increased by the addition of bensulfuron and halosulfuron compared with a single application of clomazone.
Soybean Response to Residual and In-Season Treatments of Trifloxysulfuron
Authors: Porterfield Dunk , Everman Wesley J. , Wilcut John W.
Published: July 2006

Experiments were conducted from 1998 to 2000 at Rocky Mount, NC, in weed-free environments to determine soybean tolerance to preplant (PP) applications of trifloxysulfuron and the potential for trifloxysulfuron applied preemergence (PRE) and postemergence (POST) to cotton to injure soybean grown in rotation the following year. Trifloxysulfuron at 3.75 and 7.5 g ai/ha applied PP 2 wk before seeding injured conventional soybean less than 5%, whereas no injury was observed when seeding was delayed 4 or 6 wk after PP treatment. No injury to sulfonylurea-resistant soybean (SR) was observed for any treatment. Soybean yields were not influenced by trifloxysulfuron treatment. Cotton injury was 7% or less with trifloxysulfuron applied PRE or POST at 3.75 and 7.5 g/ha. Trifloxysulfuron at 15 g/ha PRE or POST injured cotton a maximum of 14 to 18%. Trifloxysulfuron did not reduce cotton lint yields regardless of method or rate of application. Both conventional and SR soybean were not injured nor were yields influenced by trifloxysulfuron applied PRE or POST the previous year to cotton.
Comparison of Glyphosate Salts (Isopropylamine, Diammonium, and Potassium) and Calcium and Magnesium Concentrations on the Control of Various Weeds
Authors: Mueller Thomas C. , Main Christopher L. , Thompson M. Angela , Steckel Lawrence E.
Published: July 2006

Greenhouse and field experiments were conducted near Knoxville, TN, during 2002 and 2003 to investigate the effects of calcium and magnesium ions on the performance of three glyphosate formulations with and without diammonium sulfate (AMS). Weed species investigated in the greenhouse were broadleaf signalgrass, pitted morningglory, Palmer amaranth, and yellow nutsedge. Three glyphosate formulations (isopropylamine salt, diammonium salt, and potassium salt) and two glyphosate application rates (0.42 and 0.84 kg ae/ha) were applied to weeds in water fortified with either calcium or magnesium at concentrations of 0, 250, 500, 750, and 1,000 ppm. In all comparisons, there were no differences in the three glyphosate formulations. Glyphosate activity was reduced only when cation concentration was >250 ppm, and this antagonism was not observed when 2% w/ w AMS was added to the spray solution. A chemical analysis of the calcium and magnesium concentrations in water collected from farmers indicated that water samples from eight different producers contained relatively low amounts of cations, with calcium at <40 ppm and magnesium at <8 ppm. In the field results using these and other waters as the herbicide carrier, broadleaf signalgrass control was greater with the 0.84 kg ae/ha than 0.42 kg ae/ha glyphosate rate regardless of water source or addition of AMS. Pitted morningglory responded similarly to glyphosate with water from all farms and with AMS added, and the addition of AMS gave similar results for both glyphosate rates. In 2003, common cocklebur was evaluated and control was >93% regardless of glyphosate rate, water source, or AMS addition. Based on these results, the addition of AMS-based adjuvants to many glyphosate applications may not be warranted.
Alfalfa Management in No-tillage Corn
Authors: Glenn Scott , David Meyers R.
Published: July 2006

Glyphosate-resistant corn was no-till planted into alfalfa that was in the early bud stage (UNCUT) or had been cut 3 to 4 d earlier and baled for hay (CUT). Alfalfa control and corn yield were measured in nontreated plots as well as plots treated with glyphosate alone or tank-mixed with 2,4-D or dicamba applied at planting (AP) or POST. Alfalfa control was greater for all AP treatments of UNCUT compared to CUT alfalfa. Glyphosate plus dicamba applied AP controlled alfalfa better than the other AP treatments resulting in increased corn yield compared with other AP treatments. Postemergence applications of glyphosate alone or tank-mixed with 2,4-D or dicamba controlled alfalfa better 6 weeks after treatment than AP applications of the same herbicides; however, corn yield for AP treatments were similar or greater than the yield of POST applications of the same herbicides. Corn yield averaged 13% higher following herbicide applications to UNCUT compared with CUT alfalfa, so the value of alfalfa hay must be weighed against the loss of corn yield when making decisions concerning the management of an alfalfa–corn rotation.
Seasonal Changes in Carbohydrates in the Root of Canada thistle (Cirsium arvense) and the Disruption of these Changes by Herbicides
Authors: Wilson Robert G. , Martin Alex R. , Kachman Stephen D.
Published: July 2006

Roots of Canada thistle were excavated from the soil monthly from 1999 to 2001 near Scottsbluff, NE, to quantify the influence of changing soil temperature on free sugars and fructans in roots. Sucrose concentrations were low from May through August then increased in the fall and remained at high levels during winter and then declined in April as plants initiated spring growth. Changes in sucrose, 1-kestose (DP 3) and 1-nystose (DP 4) were shown to be closely associated with changes in soil temperature. During the second year of the study, average soil temperatures during the winter were colder than the first year and resulted in an increase of sucrose in Canada thistle roots. Experiments were conducted from 2001 to 2004 to determine whether there was a correlation between herbicide efficacy, time of herbicide application, and the resulting herbicide effect on root carbohydrate and Canada thistle control. Clopyralid applied in the fall reduced Canada thistle density 92% 8 months after treatment (MAT) whereas treatment made in the spring reduced plant density 33% 11 MAT. Fall application of clopyralid increased the activity of fructan 1-exohydrolase (1-FEH) in roots and was associated with a decline in sucrose, DP 4, and 1-fructofuranosyl-nystose (DP 5) 35 d after treatment (DAT). Spring application of clopyralid also resulted in a decrease of the same carbohydrates 35 DAT, but by 98 DAT, or early October, sucrose level in roots had recovered and was similar to nontreated plants. Fall application of 2,4-D or clopyralid reduced Canada thistle density 39 and 92% respectively, 8 MAT, but only clopyralid resulted in a reduction of sucrose, DP 4, DP 5, and total sugar and an increase of 1-FEH compared with nontreated plants.
Weed Control in Grape After Fall and Spring Application of Selected Herbicides
Authors: Kadir Sorkel , Al-Khatib Kassim
Published: July 2006

Soil-residual herbicides can be applied to the soil under grapevines during fall or spring before weed emergence. But, early spring moisture and warm weather conditions may enhance weed emergence before spring herbicide applications. Therefore, fall application of herbicide can be useful if the herbicides provide adequate weed control the following spring and summer. Fall and spring applications of oryzalin or norflurazon, applied alone or in combination with diuron, simazine, or oxyfluorfen, were evaluated for weed control in grape at Oskaloosa and Eudora in northeast Kansas in the 2002 to 2003 and 2003 to 2004 growing seasons. Weeds were not controlled adequately with oryzalin or norflurazon applied alone. At the end of the growing season, weed control was 10 to 20% greater when herbicides were applied in the spring than when applied in the fall. In addition, weed control with norflurazon was slightly greater than with oryzalin. In general, norflurazon or oryzalin applied in combination with simazine, diuron, or oxyfluorfen gave greater weed control than norflurazon or oryzalin applied alone. The greatest control was with norflurazon or oryzalin applied with oxyfluorfen. In general, all herbicide combinations provided similar weed control 4 mo after spring treatment in 2003 and 3 mo after spring treatment in 2004. This study showed that acceptable weed control can be achieved when norflurazon or oryzalin is applied with oxyfluorfen or diuron in the fall.
Potential for Halosulfuron to Control Eclipta (Eclipta prostrata) in Container-Grown Landscape Plants and Its Sorption to Container Rooting Substrate
Authors: Wehtje Glenn R. , Gilliam Charles H. , Grey Timothy L. , Blythe Eugene K.
Published: July 2006

Eclipta is a seed-borne summer annual that is problematic in the production of container-grown landscape plants. Halosulfuron at 70 g/ha is registered as a directed application to landscape areas but not to container-grown landscape plants. Halosulfuron was applied preemergence (PRE) to seeded eclipta and postemergence (POST) to progressively older eclipta seedlings at rates ranging from 0.18 to 100 g/ha. For halosulfuron PRE treatments, eclipta control was determined from the foliage weight of surviving seedlings. For halosulfuron POST treatments, control was determined from the weight of foliage regrowth following the removal of the treated foliage 2 wk after treatment. Nonlinear regression and log-logistic analysis indicated that the rate required for 90% control (I90) for halosulfuron PRE was 45 g/ha. For halosulfuron POST, theI90was 60 g/ha for plants having five or fewer true leaves and 98 g/ha for plants that had lateral branching from the basal crown. Analysis estimated theI90for flowering-sized eclipta exceeded 300 g/ha. Selective placement studies revealed that the phytotoxicity resulting from POST treatments occurs by foliar and root uptake, with foliar exposure having greater activity. For POST treatments that were limited to foliage-only contact, a split application increased control up to 25% compared with a single application of the same total dosage. However, control remained inadequate because the rate required for 75% control (I75) was 157 and 121 g/ha for single and split applications, respectively. Halosulfuron sorption by a pine bark–based rooting substrate, as used in container production, was 96% of the amount applied. The propensity for surface-applied halosulfuron to be leached in this substrate was evaluated by eclipta bioassay. After 2 wk, with 23 cm of cumulative irrigation and rainfall, halosulfuron was detected 12 cm below the substrate surface. The propensity for substrate-adsorbed halosulfuron to return to the water phase may also contribute to PRE activity for eclipta control.
Variable Response of Common Waterhemp (Amaranthus rudis) Populations and Individuals to Glyphosate
Authors: Smith David A. , Hallett Steven G.
Published: July 2006

Putatively resistant (PR) and putatively susceptible (PS) common waterhemp populations were grown in the greenhouse and sprayed at the three- to four-leaf stage with glyphosate (0.63 kg ae/ha). Surviving plants from PR populations and randomly selected plants from PS populations were clonally propagated and the clones were sprayed with 0.1 to 10.0 kg/ha glyphosate. The glyphosate rates required to reduce growth by 50% (GR50) among the clones were relatively similar, but the concentration required to reduce growth by 90% (GR90) ranged from 1.5 to 16.3 kg/ha. The concentration of glyphosate required to kill 90% of plants (LD90) ranged from 2.3 kg/ha to over 10.0 kg/ ha. This range of responses to glyphosate in common waterhemp clones from different parts of the Midwestern United States indicates a risk of evolution of resistance in common waterhemp populations that are repeatedly selected by applications of glyphosate in the field.
Performance of WeedSOFT for Predicting Soybean Yield Loss
Authors: Hock Shawn M. , Knezevic Stevan Z. , Martin Alex R. , Lindquist John L.
Published: July 2006

Decision support systems (DSSs) have been developed to assist producers and consultants with weed management decisions. WeedSOFT is a DSS currently used in several states in the north-central region of the United States. Accurate estimates of crop yield loss due to weed interference are required for cost-effective weed management recommendations. WeedSOFT uses competitive indices (CIs) to predict crop yield loss under multiple weed species, weed densities, and relative times of weed emergence. Performance of several WeedSOFT versions to predict soybean yield loss from weed competition was evaluated using CI values in WeedSOFT version 9.0 compared to new CI values calculated from weed dry matter, weed volume, and soybean yield loss in two soybean row spacings (19 and 76 cm) and two relative weed emergence times (at soybean emergence and first trifoliate leaf stage). Overall, new CI values improved predictions of soybean yield loss by as high as 63%. It was especially true with using new CI values based on yield loss compared to those based on weed dry matter or weed volume. However, there were inconsistencies in predictions for most weed species, suggesting that additional modifications are needed to further improve soybean yield loss predictions.
Persian Darnel (Lolium persicum) Fecundity Response to Spring Wheat, Canola, and Sunflower Interference
Authors: Holman Johnathon D. , Bussan Alvin J. , Maxwell Bruce D. , Miller Perry R. , Mickelson James A.
Published: July 2006

Persian darnel control options are limited and unmanaged populations can cause substantial crop yield loss. Integrating crop diversification and higher crop seeding rates into a cropping system might improve Persian darnel management. Field experiments were conducted to determine the effect of different crops and increased crop seeding rates on Persian darnel fecundity. Persian darnel produced up to 2,800 seeds per plant and 53,000 seeds/m2when grown without competition. Increasing crop density reduced Persian darnel tillers per plant, seed weight, and fecundity. Increasing crop density reduced Persian darnel fecundity 0.4 to 0.2% per spring wheat plant, 0.6 to 0.1% per canola plant, and 16 to 8% per sunflower plant. Persian darnel fecundity was impacted the greatest by reduced weed seedling establishment, which was caused by crop competition and seeding sunflower late in the spring preceded by a nonselective herbicide application. Results indicated delaying the seeding of spring crops or including a late-seeded warm season crop, like sunflower or safflower, in the cropping system is an effective weed management tool for reducing Persian darnel fecundity.
Weed Control in Cotton (Gossypium hirsutum) with Postemergence Applications of Trifloxysulfuron-sodium
Authors: Brecke Barry J. , Stephenson Daniel O.
Published: July 2006

Experiments were conducted in Florida from 1998 through 2000 to evaluate trifloxysulfuron-sodium applied POST for weed control in cotton. The addition of 0.25% (v/v) nonionic surfactant (NIS) to trifloxysulfuron-sodium, regardless of rate, increased sicklepod control 10 to 50% 6 and 19 wk after planting (WAP). All trifloxysulfuron-sodium treatments controlled Florida beggarweed and redweed 70 to 100% 6 and 19 WAP. Pitted morningglory was controlled 68 to 100% by trifloxysulfuron-sodium treatments; however, control was higher for treatments that contained 0.25% v/v NIS. Trifloxysulfuron-sodium provided poor control of smallflower morningglory. A sequential application of fluometuron PRE followed by trifloxysulfuron-sodium POST provided better control of smallflower morningglory than trifloxysulfuron-sodium alone 19 WAP. Cotton treated with trifloxysulfuron-sodium yielded higher than the nontreated check and early POST treatments that included 0.25% v/v NIS yielded approximately 20% higher than non-NIS treatments. Trifloxysulfuron-sodium applied POST provided season-long control of Florida beggarweed, pitted morningglory, redweed, and sicklepod with the addition of 0.25% v/v NIS but did not control smallflower morningglory in cotton.
Weed Management in Single- vs. Twin-Row Peanut (Arachis hypogaea)
Authors: Brecke Barry J. , Stephenson Daniel O.
Published: July 2006

Experiments were conducted in Florida in 2000 through 2003 to evaluate weed management systems in single- and twin-row peanut utilizing either conventional or strip tillage. Diclosulam or flumioxazin preemergence (PRE) or 2,4-DB or imazapic mid-postemergence (MPOST) or late-postemergence (LPOST) was needed for greater than 95% common cocklebur control in conventional- and strip-tillage peanut. In both tillage systems, paraquat + bentazon early-postemergence (EPOST) followed by (fb) 2,4-DB or imazapic MPOST, 2,4-DB or chlorimuron LPOST, or both was required for more than 80% late-season control of Florida beggarweed and control in twin-row was 5 to 10 percentage points above that observed with single-row peanut. Paraquat + bentazon EPOST preceded by a diclosulam or flumioxazin PRE or fb MPOST or LPOST applications provided 80% or greater control of ivyleaf morningglory, and no differences were observed between peanut planting pattern. Paraquat + bentazon EPOST fb imazapic MPOST was the only treatment that provided 90% or greater late-season sicklepod control across all years and tillage methods, and, regardless of tillage, sicklepod control was 7 percentage points better in twin- than single-row peanut. Treatments that contained diclosulam or flumioxazin PRE and paraquat + bentazon EPOST fb a MPOST or LPOST herbicide application increased peanut yield compared to nontreated in conventional- and strip-tillage peanut. Averaged over all herbicide treatments, years, and tillage methods, peanut seeded in twin rows yielded 300 kg/ha more than in single rows.
Seasonal Variation of Paraquat Photodegradation Rate on Polyethylene Mulch
Authors: Gilreath James P. , Santos Bielinski M. , Duranceau Steven J.
Published: July 2006

Field studies were conducted to determine the effect of season of the year, sunlight exposure time, and mulch color on paraquat photodegradation rate on polyethylene mulch. Experiments were established in winter, spring, and summer, with white and black polyethylene mulch, and paraquat-applied films were exposed to sunlight for 1, 4, 8, 24, 30, 48, 72, or 96 h after herbicide application. There was significant effect of the season by mulch color by time of exposure interaction on paraquat concentration recovered from mulch eluants. Winter paraquat photodegradation was lower than during the other seasons. At 48 h of sunlight exposure, predicted photodegradation on white mulch was 67, 83, and 88%, during winter, spring, and summer, respectively, whereas these values were 66, 82, and 84% on black mulch. The difference in paraquat photodegradation in winter with respect to the other seasons may be attributed to reduced ultraviolet radiation in winter, when solar radiation has to penetrate a larger atmosphere mass. In practical terms, transplanting on paraquat-applied mulch requires a minimum of 96 h during the spring and summer seasons, when concentrations were 5% or less, whereas a longer waiting period might be necessary in the winter.
Control of Invasive Weeds with Prescribed Burning
Authors: Ditomaso Joseph M. , Brooks Matthew L. , Allen Edith B. , Minnich Ralph , Rice Peter M. , Kyser Guy B.
Published: July 2006

Prescribed burning has primarily been used as a tool for the control of invasive late-season annual broadleaf and grass species, particularly yellow starthistle, medusahead, barb goatgrass, and several bromes. However, timely burning of a few invasive biennial broadleaves (e.g., sweetclover and garlic mustard), perennial grasses (e.g., bluegrasses and smooth brome), and woody species (e.g., brooms and Chinese tallow tree) also has been successful. In many cases, the effectiveness of prescribed burning can be enhanced when incorporated into an integrated vegetation management program. Although there are some excellent examples of successful use of prescribed burning for the control of invasive species, a limited number of species have been evaluated. In addition, few studies have measured the impact of prescribed burning on the long-term changes in plant communities, impacts to endangered plant species, effects on wildlife and insect populations, and alterations in soil biology, including nutrition, mycorrhizae, and hydrology. In this review, we evaluate the current state of knowledge on prescribed burning as a tool for invasive weed management.
Germination Techniques for Common Lambsquarters (Chenopodium album) and Pennsylvania Smartweed (Polygonum pensylvanicum)
Authors: Hock Shawn M. , Knezevic Stevan Z. , Petersen Chris L. , Eastin John , Martin Alex R.
Published: July 2006

A laboratory bioassay was conducted to describe the effects of cold stratification and solid matrix priming (SMP®) on the germination response of common lambsquarters and Pennsylvania smartweed seeds. Treating seeds of common lambsquarters with a combination of cold stratification and SMP resulted in 78% germination compared with 13% in control seeds. Analogous treatments of Pennsylvania smartweed seeds resulted in 22% germination compared with 1% for control. Improved germination of common lambsquarters and Pennsylvania smartweed seeds suggested that the combination of cold stratification and SMP treatments have potential for improving seed germination in other weed species that exhibit high levels of seed dormancy.
Effect of Weed Removal Timing and Row Spacing on Soil Moisture in Corn (Zea mays)
Authors: Dalley Caleb D. , Bernards Mark L. , Kells James J.
Published: July 2006

Glyphosate-resistant corn was grown in 38- and 76-cm row spacings at two locations in 2001 to examine the effect of weed competition and row spacing on soil moisture. Volumetric soil moisture was measured to a depth of 0.9 m in 18-cm increments. Glyphosate was applied when average weed canopy heights reached 5, 10, 15, 23, and 30 cm. Season-long weed interference reduced soil moisture compared with the weed free controls. At Clarksville, MI, where common lambsquarters was the dominant weed species, weed interference reduced soil moisture in the 0- to 18-cm soil depth from late June through early August and at the 54- to 72- and 72- to 90-cm depths from mid-July through the end of the season. At East Lansing, MI, where giant foxtail was the dominant weed species, weed interference reduced soil moisture at the 18- to 36-, 36- to 54-, and 54- to 72-cm soil depths from mid-June to the end of the season. Season-long weed competition reduced yields more than 90% at each location. Weeds that emerged after the 5-cm glyphosate timing reduced soil moisture and grain yield at both locations. Delaying glyphosate applications until weeds reached 23 cm or more in height reduced corn yield at both locations and soil moisture at East Lansing. Grain yields in the 10- and 15-cm glyphosate-timing treatments were equal to the weed-free corn, even though soil moisture was less during pollination and grain fill. Row spacing did not affect grain yield but did affect soil moisture. Soil moisture was greater in the 76-cm row spacing, suggesting that corn in the 38-cm row spacing may have been able to access soil moisture more effectively.
Effect of Cultural Practices on Weed Control and Crop Response in Imidazolinone-Tolerant Rice
Authors: Levy Ronald J. , Bond Jason A. , Webster Eric P. , Griffin James L. , Linscombe Steven D.
Published: July 2006

Field research was conducted for 3 yr to evaluate crop response and weed control under conventional and reduced tillage in drill- and water-seeded imidazolinone-tolerant (IT) rice culture. Imazethapyr was applied at 70 g ai/ha PRE followed by (fb) imazethapyr at 70 g/ha applied POST to three- to four-leaf rice or at 105 g/ha PRE fb 70 g/ha POST. In both conventional and reduced tillage systems, imazethapyr applied PRE fb POST at 70 g ai/ha controlled red rice, barnyardgrass, Amazon sprangletop, and rice flatsedge 87 to 99% 35 d after POST treatment (DAT). At 35 DAT, Indian jointvetch control with sequential applications of imazethapyr was as high as 70% in water-seeded rice but no more than 54% in drill-seeded rice. Tillage, seeding method, and imazethapyr rate had no effect on days to 50% heading, seeds per panicle, seed weight per panicle, or percentage of seed harvest. However, a reduction of 27% in days to 50% heading, 80% in seeds per panicle, 84% in seed weight per panicle, and 100% in percentage seed harvest index occurred when imazethapyr was not applied because of weed interference. Culm number was reduced 28%, and culm weight 32% under reduced tillage compared with conventional tillage. With sequential applications of imazethapyr at 70 g/ha, rice yield was 63% greater when rice was water-seeded compared with drill-seeded. No differences in tillage systems for weed control, days to 50% heading, seed number, seed weight per panicle, percent seed, panicle height, lodging, or yield were observed. Results of these experiments demonstrate imazethapyr will effectively control weeds in both water- and drill-seeded rice and that reduced tillage can be used without negatively affecting rice production.
Rotational Cropping Systems to Reduce Cheat (Bromus secalinus) Densities
Authors: Stone Jon C. , Peeper Thomas F. , Stone Amanda E.
Published: July 2006

In the Southern Great Plains, producers of hard red winter wheat seek sustainable methods for controlling cheat and improving economic returns. Experiments were conducted at two sites in north-central Oklahoma to determine the effect of cheat management programs, with various weed control strategies, on cheat densities and total net returns. The cheat management programs, initiated following harvest of winter wheat, included conventionally tilled, double-crop grain sorghum (Sorghum bicolorL.) followed by soybean (Glycine maxL.); and continuous winter wheat. Rotating out of winter wheat for one growing season increased yield of succedent wheat up to 32% and 42% at Billings and Ponca City, respectively. Dockage due to cheat in the succedent wheat was reduced up to 78% and 87% by rotating out of winter wheat for one growing season at Billings and Ponca City, respectively. Cheat management programs including a crop rotation with herbicides applied to the grain sorghum, except for an application of atrazine + metolachlor at Ponca City, improved total net returns over the nontreated continuous wheat option. Cheat panicles in the succedent wheat were reduced up to 87% by rotation out of winter wheat for one growing season.
Practical Changes to Single-Boom Sprayers for Zone Herbicide Application
Authors: Donald William W. , Nelson Kelly
Published: July 2006

Reduced-rate zone herbicide application (ZHA) consists of banding reduced herbicide rates between crop rows (≤ full broadcast registered rate, 1×) and banding much reduced herbicide rates over crop rows (≪ 1×). The objective of this research was to compare the mechanically complicated dual-boom ZHA sprayer with a much simpler, single-boom ZHA sprayer for controlling giant foxtail and common waterhemp in field corn in 2003 and 2004 in Missouri. The dual-boom ZHA sprayer employed two different herbicide solutions, which were propelled through two booms on separate sprayer systems to apply different herbicide rates over in-row and between-row areas while maintaining similar carrier volumes and coverage through two booms. In contrast, the single-boom ZHA sprayer is a mechanically simpler system in which both herbicide rates and carrier volumes were varied across one boom over in-row (IR) and between-row (BR) areas. In single-boom ZHA, two different nozzle tips were alternated on one boom over in-row and between-row areas, the number of nozzles per boom was doubled, and the distance between nozzles was halved compared with a conventional sprayer boom. In a 2-yr study, these different ZHA sprayers were used to apply preemergence atrazine + S-metolachlor between and over crop rows at various reduced rates (1× = 2,240 + 1,750 g ai/ha, respectively). Among all single- and dual-boom ZHA sprayer treatments and the weed-free checks, corn yields and in-row total weed cover were statistically indistinguishable for both years and for between-row total weed cover in 1 of 2 yr. In both years, a single-boom ZHA system prevented yield loss from competing weeds as effectively as the dual-boom ZHA system. The new single-boom ZHA system is a mechanically simple, inexpensive, generic alternative for reducing herbicide rates and lowering input costs.
Imidazolinone-Tolerant Rice Response to Imazethapyr Application
Authors: Levy Ronald J. , Bond Jason A. , Webster Eric P. , Griffin James L. , Zhang Wei P. , Linscombe Steven D.
Published: July 2006

Greenhouse research was conducted to evaluate shoot and root growth response of imidazolinone-tolerant (IT) rice cultivars to imazethapyr applied postemergence at various rates and application timings. Imazethapyr was applied at 70, 140, and 280 g ai/ha to IT cultivars ‘CL 121’ and ‘CL 161’ in the one- to two-leaf and three- to four-leaf growth stages. Imazethapyr applied to one- to two-leaf or three- to four-leaf rice at 70, 140, and 280 g/ha was more injurious to CL 121 than to CL 161. At 3 wk after treatment (WAT), CL 121 was injured 23 to 38% regardless of application timing. In contrast, CL 161 was injured no more than 11% at 3 WAT. Shoot:root ratio for CL 161 was not affected by imazethapyr application. For CL 121, shoot:root ratio was lower following imazethapyr at 280 g/ha than at 70 or 140 g/ha. Based on shoot fresh weight following imazethapyr at 70 g/ha, CL 161 was 1.8 times more tolerant than CL 121 at 2 WAT and 1.3 times more tolerant at 3 WAT. The IT rice cultivar CL 161 is inherently more tolerant to imazethapyr than is CL 121 based on visual injury and shoot and root growth.
Control of Tropical Soda Apple (Solanum viarum) with Aminopyralid
Authors: Ferrell Jason A. , Mullahey J. Jeffrey , Langeland Kenneth A. , Kline William N.
Published: July 2006

Experiments were conducted between 2002 and 2004 at multiple locations in Florida to determine the efficacy of aminopyralid and other herbicides on tropical soda apple (TSA) control. Aminopyralid applied at rates ≥0.08 kg ai/ha consistently provided >96% TSA control up to 335 d after treatment (DAT), while applications <0.06 kg/ha were less effective as well as inconsistent. Control of TSA with aminopyralid was often not statistically different from control with triclopyr, picloram, or dicamba. However, these responses were likely due to the variability in TSA control by triclopyr, picloram, or dicamba across several locations. For example, the standard error of the mean for TSA control with picloram at 335 DAT was 8, compared to 1 for aminopyralid. Herbicides were applied in April, January, and June, but time of year did not affect the efficacy of aminopyralid. Aminopyralid possesses soil residual activity and controlled 98% of germinating seedlings at 75 DAT, compared to 0% control for triclopyr or 2,4-D + dicamba. Therefore, aminopyralid controlled TSA from foliar applications and soil residual activity more consistently than any other herbicide evaluated in these experiments.