bluuebunny/crossref_metadata_2025 huggingface dataset:
Relative Dissipation of Acetochlor, Alachlor, Metolachlor, and SAN 582 from Three Surface Soils
Authors: Mueller Thomas C. , Shaw David R. , Witt William W.
Published: March 2018

The dissipation of four commonly used soil-applied herbicides was examined in a standardized field experiment in three southern states (Kentucky, Mississippi, and Tennessee). Averaged over the three soils and 2 yr, the relative order of increasing half-life defined as time for 50% disappearance in days (DT50) was acetochlor (6.3 d) = alachlor (6.3 d) = SAN 582 (7.3 d) < metolachlor (13.7 d). Metolachlor was the most persistent in the soil surface, and this could potentially translate into greater duration of weed control into the growing season. All examined herbicides had a DT50that averaged less than 14 d in all states in both years, so full-season weed control of susceptible species would not be expected. Rapid herbicide degradation was encouraged in these field sites by adequate to excessive soil moisture and warm temperatures throughout the sampling interval. The soils also were light textured, and the lower adsorption of the herbicide allowed for degradation ease and perhaps leaching below the sampling depth.
An Integrated Weed Management Approach to Managing Foxtail Barley (Hordeum jubatum) in Conservation Tillage Systems
Authors: Blackshaw Robert E. , Semach Greg , Li Xiangju , O'Donovan John T. , Harker K. Neil
Published: March 2018

A 4-yr field experiment was conducted to determine the merits of combining cultural and chemical controls to manage foxtail barley in reduced-tillage systems. Factors studied were crop row spacing, seeding rate, and application rate and timing of glyphosate within a spring wheat-flax cropping sequence. Glyphosate applied preseeding at 400 or 800 g/ha killed foxtail barley seedlings but only suppressed established perennial plants. Glyphosate applied postharvest at 800 g/ha killed 60 to 70% of established plants. Combinations of preseeding and postharvest glyphosate gave the greatest reductions in foxtail barley biomass and seed production and resulted in the greatest increases in crop yield. Including flax in the rotation allowed use of grass herbicides such as quizalofop or sethoxydim that effectively controlled foxtail barley seedlings and provided some suppression of perennial plants. An increase in wheat seeding rate from 75 to 115 kg/ha reduced foxtail barley growth and increased wheat yield in 3 of 4 yr. Increasing the flax seeding rate from 40 to 80 kg/ha or reducing wheat and flax row spacing from 30 to 20 cm provided little benefit in managing foxtail barley or increasing crop yield. A multiyear approach combining agronomic practices and timely use of herbicides should allow growers to effectively manage foxtail barley in annual cropping systems using conservation tillage.
Integrated Johnsongrass (Sorghum halepense) Management in Field Corn (Zea mays) with Reduced Rates of Nicosulfuron and Cultivation
Authors: Rosales-Robles Enrique , Chandler James M. , Senseman Scott A. , Prostko Eric P.
Published: March 2018

Johnsongrass, a tall, coarse, perennial grass, is the second most common and troublesome weed in field corn in Texas. Field experiments were conducted in 1996 to 1998 to evaluate an integrated johnsongrass management program in bedded and irrigated field corn. Nicosulfuron at 26.3 g ai/ha applied banded over the row to 50% of the planted area plus one cultivation resulted in johnsongrass control of aboveground and rhizome biomass and in corn yield comparable to the labeled rate (35 g ai/ha) when applied two consecutive years in the same plots. This treatment reduced cost 27% and reduced herbicide input 62% compared to nicosulfuron applied broadcast at labeled rate without cultivation. Economic benefits of this johnsongrass management program are promising for field corn producers.
The Potential for Clomazone Use in Rice (Oryza Sativa)
Authors: Webster Eric P. , Baldwin Ford L. , Dillon Tomilea L.
Published: March 2018

Clomazone was applied preplant incorporated, preemergence, delayed preemergence, or postemergence and compared to pendimethalin, quinclorac, and thiobencarb for control of barnyardgrass in rice. Seven days after the clomazone postemergence application, all clomazone treatments except those applied postemergence controlled barnyardgrass ≥ 86%. At 49 d after the postemergence application, control of barnyardgrass with 0.56 and 0.67 kg/ha clomazone postemergence improved to 92 and 93%, respectively. Clomazone and quinclorac applied delayed preemergence generally controlled barnyardgrass less than 70%. Visible injury to rice was ≤ 18% 7 d after emergence and had declined to less than 10% when evaluated 7 d after postemergence treatments. Rice yields were higher with all treatments compared to the nontreated control.
Influence of Selected Adjuvants on Disease Severity byPhoma herbarumon Dandelion (Taraxacum officinale)
Authors: Neumann Silke , Boland Greg J.
Published: March 2018

Phoma herbarumwas evaluated as a potential biological control agent for dandelion (Taraxacum officinale) in turf. A preliminary controlled environment study identified selected adjuvants that enhanced disease severity byP. herbarum.Subsequently, these adjuvants were evaluated for disease enhancement under field conditions. Adjuvants evaluated included gluten flour, liposome, guar gum from ground guar (Cyamopsis tetragonoloba), durum (Triticum durum), and pectin. Regression analysis revealed a significant (P= 0.05) increase in disease severity byP. herbarumwhen formulated with gluten Hour, guar gum, or durum semolina compared to treatment with 20% mycelium in potato (Solanum tuberosum) dextrose broth (PDB) alone. No phytotoxicity to dandelion was observed among the adjuvant controls.
Optimizing Alcohol Ethoxylate Surfactant Activity at Low Doses
Authors: Green Jerry M.
Published: March 2018

Certain linear alcohol ethoxylate surfactants with large hydrophobes enhanced nicosulfuron activity on giant foxtail (Setaria faberi) more effectively at low doses than surfactants with small hydrophobes and commercial standards. The most effective surfactants had a C16–18 hydrophobe and 12 to 30 moles of ethoxylation or a C24 hydrophobe with 13 moles of ethoxylation. Response curve analysis showed these linear alcohol ethoxylate surfactants were five- to 20-fold more active on a dose basis than currently used commercial surfactants.
Dry Pea (Pisum sativumL.) Response to Low Rates of Selected Foliar- and Soil-Applied Sulfonylurea and Growth Regulator Herbicides
Authors: Al-Khatib Kassim , Tamhane Ajit
Published: March 2018

Field experiments on dry pea (Pisum sativum) were conducted at five locations across the United States in 1995 and 1996 to investigate the effects of low rates of chlorsulfuron, thifensulfuron, and dicamba applied postemergence and of chlorsulfuron, metsulfuron, and clopyralid applied preplant incorporated in the soil on pea plants. Although chlorsulfuron, thifensulfuron, and dicamba caused significant injury symptoms on pea plants, they had little effect on yield. The lowest rates of foliar applications that caused observable symptoms were 0.035, 0.086, and 1.56 g ai/ha for chlorsulfuron, thifensulfuron, and dicamba, respectively, whereas chlorsulfuron, thifensulfuron, and dicamba rates that reduced pea yield by 25% were 0.18, 1.36, and 25 g/ha, respectively. Clopyralid caused more injury symptoms than metsulfuron or chlorsulfuron with soil application. However, the lowest rates of chlorsulfuron, metsulfuron, and clopyralid that caused observable symptoms were lower than the rates that reduced yield. This study showed that pea plants can sustain some level of plant injury without a large reduction in yield.
Characterization of the Spray Droplet Spectra and Patterns of Four Venturi-Type Drift Reduction Nozzles
Authors: Etheridge Robert E. , Womac Alvin R. , Mueller Thomas C.
Published: March 2018

Laboratory studies were conducted using a Malvern laser droplet/particle size analyzer to determine the droplet spectra of several venturi-type drift reduction nozzles compared to a standard single, elliptical-orifice flat fan nozzle. Spray solutions of glufosinate, glyphosate, and paraquat were applied through all combinations of five nozzle types (four drift reduction), three tip sizes, and four application pressures. Nozzles were also evaluated for pattern uniformity using water plus surfactant at one pressure. When averaged over herbicide, tip size, and pressure the venturi nozzles collectively produced larger volume median diameter (VMD) droplets than the standard nozzle. The percentage of spray volume in droplets < 205 μm was less for the venturi nozzles (17%) than for the standard nozzle (65%) when averaged across all factors. The order of herbicides producing the largest droplets was paraquat (470 μm) > glyphosate (460 μm) > glufosinate (400 μm), as measured by VMD. The venturi nozzles were more variable in their spray volume distribution than the standard nozzle. Utilization of venturi-type nozzles may minimize the drift potential of the herbicides evaluated but could also lead to uneven herbicide application and subsequent erratic weed control.
Response of Peanut (Arachis hypogaea) and Selected Weeds to Diclosulam
Authors: Bailey William A. , Wilcut John W. , Jordan David L. , Swann Charles W. , Langston Vernon B.
Published: March 2018

Field studies were conducted at five locations in North Carolina and Virginia during 1996 and 1997 to evaluate weed control, peanut (Arachis hypogaea) response, and peanut yield following diclosulam applied preplant incorporated (PPI) and in systems with commercial herbicide standards. All plots received a PPI treatment of ethalfluralin at 840 g ai/ha. Ethalfluralin plus diclosulam controlled entireleaf morningglory (Ipomoea hederaceavar.integriuscula), ivyleaf morningglory (I. hederacea), pitted morningglory (I. lacunosa), common lambsquarters (Chenopodium album), eclipta (Eclipta prostrata), and prickly sida (Sida spinosa) as well as and frequently better than ethalfluralin PPI followed by (fb) acifluorfen plus bentazon postemergence (POST), paraquat plus bentazon early postemergence (EPOST) fb imazapic POST, or imazapic POST. Systems with ethalfluralin plus diclosulam PPI at 26 g ai/ha fb acifluorfen plus bentazon POST controlled a broader spectrum of weeds and yielded greater than systems of ethalfluralin PPI fb imazapic POST or ethalfluralin PPI fb acifluorfen plus bentazon POST. Peanut exhibited excellent tolerance to diclosulam PPI at 17, 26, or 35 g/ha.
Influence of Adjuvants on Interactions of Sethoxydim with Selected Broadleaf Herbicides Used in Corn (Zea mays)
Authors: Corkern Christopher B. , Jordan David L. , Griffin James L. , Vidrine P. Roy , Williams Bill J. , Reynolds Daniel B.
Published: March 2018

Field experiments were conducted during 1996 and 1998 to determine the effect of atrazine, bentazon, atrazine + bentazon, the amine salt of 2,4-D, and bromoxynil on broadleaf signalgrass and barnyardgrass control when applied in mixture with sethoxydim. Herbicide combinations were applied with crop oil concentrate, crop oil concentrate + ammonium sulfate, or BCH 815. Bentazon and atrazine + bentazon reduced broadleaf signalgrass and barnyardgrass control by sethoxydim. Bromoxynil reduced barnyardgrass control but had no affect on broadleaf signalgrass control. Including ammonium sulfate with crop oil concentrate or substituting BCH 815 for crop oil concentrate increased barnyardgrass and broadleaf signalgrass control by sethoxydim when applied with bentazon. Ammonium sulfate and BCH 815 increased barnyardgrass control when sethoxydim was applied with bromoxynil but did not affect control when sethoxydim was applied with atrazine + bentazon. Atrazine and the ammonium salt of 2,4-D did not reduce barnyardgrass and broadleaf signalgrass control by sethoxydim regardless of adjuvant.
Influence of Deleterious Rhizobacteria on Leafy Spurge (Euphorbia esula) Roots
Authors: Brinkman Mark A. , Clay Sharon A. , Kremer Robert J.
Published: March 2018

Rhizobacteria have been shown to be phytotoxic to leafy spurge in laboratory assays. This field study investigated the influence of two strains ofPseudomonas fluorescens[Trevisan, (Migula)], deleterious rhizobacteria (DRB), on root weight, root bud number, and root carbohydrate content of leafy spurge at three sites located in northeast and north-central South Dakota. Soils were inoculated with 2 g of starch-based granules containing no bacteria or starch granules containing 108colony-forming units (cfu)/g of either bacterial strain LS102 (Montana origin) or LS174 (South Dakota origin). Bacterial strains were detected on root samples from treated areas. Root weight and root carbohydrate content were reduced about 20% compared to roots from control plots.
Economic Importance of Managing Spatially Heterogeneous Weed Populations
Authors: Lindquist John L. , Dieleman J. Anita , Mortensen David A. , Johnson Gregg A. , Wyse-Pester Dawn Y.
Published: March 2018

Three methods of predicting the impact of weed interference on crop yield and expected economic return were compared to evaluate the economic importance of weed spatial heterogeneity. Density of three weed species was obtained using a grid sampling scheme in 11 corn and 11 soybean fields. Crop yield loss was predicted assuming densities were homogeneous, aggregated following a negative binomial with known population mean and k, or aggregated with weed densities spatially mapped. Predicted crop loss was lowest and expected returns highest when spatial location of weed density was utilized to decide whether control was justified. Location-specific weed management resulted in economic gain as well as a reduction in the quantity of herbicide applied.
Genetic Diversity and Origin of Siam Weed (Chromolaena odorata) in Australia
Authors: Scott Leon J. , Lange Corinna L. , Graham Glenn C. , Yeates David K.
Published: March 2018

Asynchronous flowering was noted in a recently discovered infestation of siam weed in north Queensland. This may indicate some genetic diversity in the infestation, increasing concerns about the origin of the infestation. Internal transcribed spacer 1 (ITS1) sequence data were obtained for siam weed individuals from north Queensland, Indonesia, Thailand, South Africa, Ivory Coast, Brazil, Colombia, and the U.S. The ITS1 region is 258 base pairs long, and the populations that flower at different times in north Queensland differ by four base substitutions. The genotype common in north Queensland is also reported throughout the native and introduced ranges. The other genotype is reported only in north Queensland and southern Brazil. These data, in conjunction with prior investigations into possible origins, indicate that Brazil is the most likely source of the infestation in Australia.
Effect ofAlternaria cassiae, Pseudocercospora nigricans, and Soybean (Glycine max) Planting Density on the Biological Control of Sicklepod (Senna obtusifolia)
Authors: Pitelli Robinson A. , Charudattan R. , Devalerio James T.
Published: March 2018

The interactions of two fungal biocontrol agents,Alternaria cassiaeandPseudocercospora nigricans, and soybean planting density on sicklepod mortality and dry weight were studied in the field over 2 yr. The experimental field was divided into three equal areas: one without soybean and two where the soybean was sown in densities of 20 and 36 seeds per meter row with a 0.95-m row spacing. The fungi were sprayed alone or in a mixture at three growth stages of sicklepod plants grown at three levels of crop interference resulting from the three soybean planting densities. The fungal treatments were: an untreated control,A. cassiae(105spores/m2),P. nigricans(3.3 g mycelium/m2), and the mixture of these two fungi. Sicklepod was at the cotyledonary leaf, two-leaf, and four-leaf stages when treated.Alternaria cassiaewas most effective in reducing both sicklepod survival and dry weight. The mixture ofP. nigricansandA. cassiaewas generally comparable to but not better thanA. cassiaealone in killing the weed (mortality) and reducing its growth (dry weight). Soybean density did not have significant effects on the mortality or the dry weight of sicklepod. Thus, there is no advantage to combining the highly effective biocontrol agentA. cassiaewith the less effectiveP. nigricansor with soybean interference to control sicklepod. However, the results validate the efficacy ofA. cassiaeby itself as a bioherbicide.
Weed Management ofAmaranthusspp. in Corn (Zea mays)
Authors: Vizantinopoulos S. , Katranis N.
Published: March 2018

Field experiments were conducted from 1987 to 1990 to investigate the combination of cultural and chemical methods for control ofAmaranthusspp. in corn. The tolerance of corn hybrids to herbicides or herbicide combinations was dependent on application rate. The early season threshold level for a mixed population ofAmaranthusspp. occurred 3.5 wk after emergence. Density ofAmaranthusspp. from 155 to 495 plants/m2caused corn yield reduction of 50%. A quadratic model was derived relating percentage of yield reduction vs. duration of weed competition. The results emphasize the importance of using herbicides, cultural practices, and competition thresholds for an integrated weed control approach ofAmaranthusspp. in corn.
Total Postemergence Weed Control in Imidazolinone-Resistant Corn (Zea mays)
Authors: Krausz Ronald F. , Kapusta George
Published: March 2018

Field experiments were conducted in 1994 and 1995 to evaluate weed control in imidazolinone-resistant corn with postemergence applications of imidazolinone and sulfonylurea herbicides. Imazethapyr controlled 100% of redroot pigweed, jimsonweed, and eastern black nightshade. Control of fall panicum with imazethapyr was inconsistent, with control ranging from 42 to 85%. Imazethapyr provided less than 55% control of common lambsquarters and 43% of large crabgrass. Imazethapyr plus either atrazine, 2,4-D, or dicamba increased control of common lambsquarters compared to imazethapyr alone. Fall panicum control was > 95% with nicosufluron. CGA-152005 and MON 12000 did not control eastern black nightshade. In 1995, corn yield was greater with the hand-weeded check compared to all herbicide treatments. The greatest return over herbicide cost with imazethapyr was obtained with imazethapyr plus atrazine. Nicosulfuron plus CGA-152005 provided the greatest return over herbicide cost when averaged across years.
Herbicide Combinations for Preharvest Weed Desiccation in Early Maturing Soybean (Glycine max)
Authors: Ellis Jeffrey M. , Shaw David R. , Barrentine William L.
Published: March 2018

Field experiments were conducted at three locations in Mississippi in 1995 and 1996 to evaluate labeled and alternative herbicides and herbicide combinations for weed desiccation prior to soybean harvest. Weeds evaluated included pitted morningglory, hemp sesbania, spotted spurge, common cocklebur, and sicklepod. Soybean yield and harvestable soybean losses were not affected by preharvest herbicide treatments, spray volume, or surfactant concentration. Soybean moisture was most consistently reduced by glufosinate compared to the untreated and other herbicides and herbicide combinations evaluated. Most desiccation treatments at Stoneville and Brooksville resulted in foreign material similar to the weed-free check. Glufosinate at 0.84, 1.1, and 1.4 kg ai/ha desiccated all weeds evaluated 90% or more with no differences among rates. The addition of 3.4 or 6.7 kg ai/ha sodium chlorate to 0.28 kg ai/ha paraquat, 1.1 and 2.2 kg ai/ha glyphosate, or 0.28 and 0.56 kg ai/ha oxyfluorfen increased desiccation of most weeds evaluated, with no difference between sodium chlorate rates. In some instances, reducing application volume from 281 to 94 L/ha improved pitted morningglory desiccation when 0.28 g/ha paraquat was applied alone. There were no differences between 0.25 and 0.50% (v/v) surfactant for most parameters evaluated.
Mechanical and Chemical Weed Control Systems for Kidney Bean (Phaseolus vulgaris)
Authors: Burnside Orvin C. , Wiens Melvin J. , Krause Norman H. , Weisberg Sanford , Ristau Eric A. , Johnson Michelle M. , Sheets Rebecca A.
Published: March 2018

Various chemical and mechanical weed control treatments for kidney bean production were evaluated on irrigated, sandy loam sites from 1993 to 1995 near Staples, MN. Weed biomass can be controlled either mechanically or chemically, but a combination of the two gave the most effective and dependable weed control over years. Good weed control by either mechanical or chemical means reduced white mold infection of dry bean because of better aeration of dry bean plants and thus less favorable conditions for infection. Dry bean seed yields were inversely related to weed yields, and weed competition was similar from indigenous stands of either grass or broadleaf weeds. Row cultivation was more effective than rotary hoeing for controlling weeds, reducing white mold infection of dry bean, and increasing dry bean seed yields.
Leafy Spurge (Euphorbia esula) Control with Quinclorac
Authors: Kuehl Brian D. , Lym Rodney G.
Published: March 2018

Quinclorac is a systemic herbicide registered to control annual grass and broadleaf weeds in rice. Field research was conducted to determine the most effective quinclorac treatment for leafy spurge control. Leafy spurge control 12 mo after treatment (MAT) averaged 38 and 77% when quinclorac was applied at 0.56 and 1.7 kg ae/ha, respectively. Quinclorac applied with the crop-oil-based adjuvant Scoil provided similar leafy spurge control compared to quinclorac applied alone. Quinclorac plus Scoil applied with picloram provided better leafy spurge control than quinclorac plus Scoil alone. The optimum date for fall treatment with quinclorac is broad. Quinclorac at 1.1 kg/ha plus Scoil at 2.3 L/ha applied on September 1, September 15, October 1, and October 15 provided similar leafy spurge control and averaged 56% 12 MAT.
Varying Surfactant Type Changes Quizalofop-P Herbicidal Activity
Authors: Green Jerry M.
Published: March 2018

Varying the type of nonionic surfactant greatly changed the biological activity of the ethyl ester of quizalofop-P on giant foxtail, barnyardgrass, and corn. These studies statistically evaluated 22 surfactants with widely different chemical, physical, and surface properties. Of the 14 surfactant properties analyzed, dynamic surface tension was the most important to enhance quizalofop-P activity. Alcohol ethoxylate surfactants like Genapol® 24-L-92 and Tergitol® 15-S-7 were among the most effective adjuvants. These surfactants performed significantly better than the commercial nonionic surfactant, Induce®, and equal to a high-quality petroleum crop oil concentrate, Agri-dex®. These surfactants offer a lower dose option to crop oil concentrates and a more effective surfactant alternative for mixtures that prohibit crop oil concentrates.
Response of BAR-Transformed Rice (Oryza sativa) and Red Rice (Oryza sativa) to Glufosinate Application Timing
Authors: Sankula Sujatha , Braverman Michael P. , Linscombe Steven D.
Published: March 2018

Glufosinate at 2.2 kg ai/ha injured rice transformed with the BAR gene more when applied to one- to two-leaf (23 to 26%) than to three- to four-leaf (13 to 19%) plants. Visible injury was least when applications were made at boot stage (3 to 14%). However, applications at boot stage caused an average grain yield reduction of 16%. Most treatments did not influence rice plant height. Among single applications (0.3, 0.4, 0.6, 0.8, and 1.1 kg/ha), 1.1 kg/ha glufosinate at three- to four-leaf stage of red rice resulted in greater control (91%) than at panicle initiation (74%) or at boot stage (77%). Injury to red rice was two to 11 times greater than the injury to BAR-transformed rice depending on glufosinate rate and application timing.
Changes in the Weed Species Composition of the Southern United States: 1974 to 1995
Authors: Webster Theodore M. , Coble Harold D.
Published: March 2018

The Southern Weed Science Society has conducted an annual survey of the most troublesome weeds in several major crops since 1971. The objective of this summary was to characterize shifts in weed populations over a 22-yr period in four major agronomic crops. For corn, soybean, cotton, and peanut, the largest increases in rank as the most troublesome weeds were found with sicklepod and bermudagrass. The largest decreases were found with johnsongrass, crab-grasses, and common cocklebur. Morningglories and nutsedges remained relatively constant weed problems over the 22-yr period. Sicklepod, nutsedges, and morningglories were the three most troublesome weeds averaged over all crops because they are so well established and relatively difficult to control. Pigweeds (Palmer amaranth, sandhills amaranth, tumble pigweed, and water-hemps) have become increasingly important in soybean, peanut, and cotton in a limited number of states.
Rimsulfuron and Metribuzin Efficacy in Transplanted Tomato (Lycopersicon esculentum)
Authors: Ackley John A. , Wilson Henry P. , Hines Thomas E.
Published: March 2018

In field studies in 1991, 1992, and 1993, rimsulfuron at 26 and 35 g ai/ha, sequentially at 26 g/ha, at 26 g/ha plus metribuzin at 280 g ai/ha, and metribuzin at 280 g/ha were evaluated POST for weed control in transplanted ‘Agriset’ tomato. Common lambsquarters was controlled by rimsulfuron at 35 g/ha. Rimsulfuron plus metribuzin gave consistent control of common ragweed, but jimsonweed control was inconsistent and goosegrass control was generally low. Rimsulfuron treatments caused slight (< 12%) temporary injury to new terminal growth of tomato. Yield of tomato fruit was consistently high in the metribuzin, metribuzin plus rimsulfuron, and rimsulfuron sequential treatments. In greenhouse studies, giant foxtail and large crabgrass control by rimsulfuron was above 95 and 85%, respectively, but goosegrass was not controlled. Height of four tomato cultivars was not reduced, but dry weight of ‘Floradade’ and ‘Sunbeam’ was reduced by rimsulfuron.
“Acceptable” Levels of Spotted Knapweed (Centaurea maculosa) Control
Authors: Sheley Roger L. , Jacobs James S.
Published: March 2018

Competition between bluebunch wheatgrass and spotted knapweed was quantified using three addition series experiments in an environmental chamber. Using two density matrices, spotted knapweed plants were thinned by either 45 or 90% of their original densities 40 d after emergence. Another matrix of density combinations was not thinned. All plant material was harvested 90 d after thinning. Spotted knapweed was about four times more competitive than bluebunch wheatgrass. Reducing spotted knapweed by 45% did not alter the competitive relationship between the two species. We believe remaining knapweed individuals captured the majority of the newly available resources. Ninety percent reduction was necessary to shift the competitive relationship in favor of bluebunch wheatgrass. Successful integrated spotted knapweed management must exploit key mechanisms and processes directing plant community dynamics, in conjunction with weed density reduction, if communities are to be shifted toward those that are desired.
Effects of Purple Nutsedge (Cyperus rotundus) on Tomato (Lycopersicon esculentum) and Bell Pepper (Capsicum annuum) Vegetative Growth and Fruit Yield
Authors: Morales-Payan Jose P. , Santos Bielinski M. , Stall William M. , Bewick Thomas A.
Published: March 2018

Additive series experiments were conducted under greenhouse conditions to determine the effect of season-long interference of different initial population densities of purple nutsedge on the shoot dry weight and fruit yield of tomato and bell pepper. Purple nutsedge densities up to 200 plants/m2linearly reduced shoot dry weight at flowering and fruit yield of both crops as weed density increased. Both variables were directly correlated, and for each percentage unit of tomato shoot dry weight loss at flowering, fruit yield was reduced 1.24 units, whereas for bell pepper this relationship was 1 to 2.01. Total shoot and tuber biomass of purple nutsedge increased as density increased. The presence of either crop caused a decline in the total shoot dry weight accumulation of purple nutsedge, with tomato producing a higher degree of loss than bell pepper to the weed. Fruit yield losses due to purple nutsedge interference reached 44% for tomato and 32% for bell pepper.
Control of Quackgrass (Elytrigia repens) and Field Mint (Mentha arvensis) with Glyphosate Applied Preharvest
Authors: Ivany Jerry A. , Doohan Douglas J.
Published: March 2018

Field experiments showed that quackgrass could be controlled by glyphosate applied preharvest to barley. In separate experiments, field mint was controlled by glyphosate applied pre- and postharvest to barley and wheat. Suppression of quackgrass regrowth one year following treatment was 90% or greater when glyphosate was applied at 0.9 kg ai/ha alone or at 0.45 kg ai/ha in combination with both tallow amine ethoxylate at 0.5% of total spray volume and ammonium sulfate at 3 kg/ha. Field mint shoot counts were reduced 84% the year following treatment when glyphosate was applied at 0.25 kg ai/ha and 95% when applied at 1.0 kg ai/ha. Suppression of field mint shoot regrowth the following year was 84% when glyphosate was applied postharvest and 93% when applied preharvest. Addition of tallow amine ethoxylate did not improve field mint control. Glyphosate applied preharvest to barley and wheat at less than 30% grain moisture content had no effect on grain yield.
A Rapid Bioassay for Selective Algicides
Authors: Schrader Kevin K. , De Regt Marjan Q. , Tucker Craig S. , Duke Stephen O.
Published: March 2018

Cyanobacteria (blue-green algae) are undesirable in ponds used to raise fish for human food. Management of cyanobacterial communities in aquaculture ponds has been hindered by the small number of herbicides approved for use in food-fish ponds and by the lack of selectivity toward cyanobacteria for those herbicides that are approved for that use. To facilitate development of additional management options, a rapid bioassay utilizing 96-well cell culture plates was developed for screening herbicides and other phytotoxins for selective toxicity toward cyanobacteria.Oscillatoriacf.chalybeaandSelenastrum capricornutumwere chosen as representatives of cyanobacteria (Cyanophyta) and green algae (Chlorophyta), respectively. In the bioassay, wells of the cell culture plates were inoculated with cyanobacterial or unialgal culture. One of five herbicides (atrazine, diuron, endothall, fluridone, or paraquat) was then added to the wells at various concentrations, and absorbance (650 nm) was measured at 24-h intervals. Growth of treated cultures relative to untreated cultures was used to determine relative toxicity of the herbicide to the two organisms. Paraquat was the most selective of the herbicides tested and was over 10-fold more toxic toO.cf.chalybeathan toS. capricornutum. This method was demonstrated to be a rapid, effective, and highly reproducible bioassay to identify selective algicides.
Growth of Containerized Landscape Plants Is Influenced by Herbicides Residues in Irrigation Water
Authors: Bhandary Rajgopal M. , Whitwell Ted , Briggs Jeanne
Published: March 2018

Herbicides play an important role in the production of nursery crops by reducing weed problems and improving production efficiency. Herbicides applied to nursery crops may move in runoff water into retention basins, which are used to irrigate container plants. Studies investigated the growth and development of containerized landscape plants subjected to irrigation water containing herbicide residues. Containerized dwarf gardenia, Snow azalea, Buccaneer azalea, Hellers Japanese holly, fountain grass, and daylily were grown in fine pine bark medium in the greenhouse and were irrigated with water containing 1 mg/L and 10 mg/L of oryzalin, oxyfluorfen, and isoxaben. Fountain grass and daylily were the most sensitive to herbicide application with reduced root and shoot growth. Oryzalin was the most phytotoxic to fountain grass followed by oxyfluorfen and isoxaben. Oryzalin and oxyfluorfen at 10 mg/L reduced the growth index of fountain grass. Oryzalin was the most phytotoxic herbicide to daylily, followed by isoxaben and oxyfluorfen. Only the high rate (10 mg/L) of oryzalin reduced the growth index of daylily. Among woody species, the root weights of Hellers holly were reduced by 10 mg/L of isoxaben. The growth of other woody species was not affected by the herbicides.
Image Analysis of Leafy Spurge (Euphorbia esula) Cover
Authors: Birdsall Jennifer L. , Quimby Paul C. , Rees Norman E. , Svejcar Tony J. , Sowell Bok F.
Published: March 2018

We examined whether image analysis could separate leafy spurge from other plant species and objects by comparing image analysis to the ocular method of estimating cover. Image analysis was acceptably precise at low and medium cover levels. Image analysis was as repeatable as the ocular method at all sites and cover levels and acceptably reliable at low and medium cover levels but estimated cover lower by 12 to 22% than the ocular method at high cover levels. The average error levels of image analysis and the ocular method did not differ. Estimating leafy spurge cover with a 10% error required only 20 quadrats when image analysis was used, while twice as many quadrats were needed when cover was measured ocularly. Image analysis was recommended as a measurement tool because quantification was efficient, the equipment is inexpensive, and the color prints provide a permanent photo record of the study.
Quality Control Procedures in Herbicide Field Dissipation Studies
Authors: Blumhorst Michael R. , Mueller Thomas C.
Published: March 2018

Characterization of herbicide dissipation under field conditions is an important component in determining the environmental impact of herbicides, and much information is available on this subject. However, this research area could be improved by standardizing and implementing several quality control procedures. The purpose of this review is to evaluate the recent literature on herbicide dissipation published in journals of the Weed Science Society of America. This review is not comprehensive with respect to all experimental parameters associated with field dissipation studies, but it is aimed at addressing specific areas of concern in the experimental approach to this research.
Evaluating the EPA's Comparative Product Performance Testing Guidelines for Herbicides in Snap Bean (Phaseolus vulgaris)
Authors: Bellinder Robin R. , Arsenovic Marija , Kirkwyland Jonathan J. , Wallace Russell W.
Published: March 2018

Following suggested guidelines developed by the Environmental Protection Agency (EPA), comparative snap bean herbicide performance field trials were conducted from 1993 to 1995 in New York. Data were obtained on crop injury, weed control, and weed biomass, and crop yield, quality, and losses during harvest. Trifluralin, EPTC, and pendimethalin applied preplant incorporated (PPI) and applications of metolachlor applied preemergence (PRE) provided less than adequate control of redroot pigweed, common lambsquarters, and hairy galinsoga. Cultivation improved weed control with PPI and PRE applications. Metolachlor + fomesafen PRE provided good control of hairy galinsoga, adequate redroot pigweed control, and marginal control of common lambsquarters. Fomesafen applied postemergence (POST), combinations of metolachlor applied PRE with fomesafen or bentazon applied POST, and fomesafen + bentazon applied POST adequately controlled the three weed species without cultivation. Herbicide treatments had little measurable impact on snap bean quality or losses during harvest. Information from product comparison trials may be useful in developing recommendations for growers but may prove less than adequate in providing data necessary for a thorough evaluation of the relative benefits of individual herbicides as intended by EPA guidelines. Difficulties were encountered in following the guidelines, and costs of conducting the product comparison trials for a single crop in one growing region exceeded $90,000 over 3 yr.
Tolerance of Sweet Corn (Zea mays) Cultivars to Rimsulfuron
Authors: O'sullivan John , Thomas Robert J. , Bouw William J.
Published: March 2018

Field studies were conducted in 1993 and 1994 to evaluate the tolerance of 16 sweet corn cultivars, representing a range of genotypes, to rimsulfuron applied postemergence (POST) at 12.5 and 25 g ai/ha. There was a significant cultivar by herbicide interaction for visual plant injury, plant height, and yield. ‘Merit’ and ‘Silver Extra Sweet’ were the most sensitive cultivars, with rimsulfuron resulting in complete plant mortality regardless of application dose. ‘Golden Jubilee,’ ‘King Arthur,’ ‘Ivanhoe,’ and ‘Zenith’ were less sensitive. Ten cultivars were tolerant to applications of rimsulfuron at 12.5 g/ha. Sensitivity to rimsulfuron increased as application dose increased.
Systems for Returning Conservation Reserve Program Land to Wheat (Triticum aestivum) Production
Authors: Medlin Case , Peeper Thomas F. , Stiegler James H. , Solie John B.
Published: March 2018

Experiments were conducted near Duke and Forgan, OK, on land enrolled in the Conservation Reserve program (CRP) that had been seeded to Old World bluestem (OWB) to evaluate tillage systems for returning CRP grassland to winter wheat production. Glyphosate controlled OWB 72% or less in no-till (NT) wheat. Disk tillage (DT) and moldboard plow tillage (MPT) for wheat seedbed preparation controlled OWB 87 and 99%, respectively, at Forgan and 96 and 100%, respectively, at Duke. At Forgan, OWB control in NT was higher when glyphosate was applied in July than when applied in May. Soil water content to a depth of 120 cm at planting was as high in DT and MPT without herbicide as in NT with 1,680 g ae/ha glyphosate. Within NT and MPT, glyphosate did not consistently increase soil water content compared to the respective nontreated checks. In DT, soil water content to a depth of 120 cm was greater following glyphosate at 1,680 g/ ha than without glyphosate. Wheat density was greater in DT and MPT than in NT. Compared to the NT no herbicide treatment, tillage tripled wheat yields. Wheat yields were often greater where glyphosate was applied before tillage. No-till wheat production immediately after CPR in Oklahoma without prior destruction of accumulated OWB residue does not appear feasible.
Correlation of Leaf Damage with Uptake and Translocation of Glyphosate in Velvetleaf (Abutilon theophrasti)
Authors: Feng Paul C. C. , Ryerse Jan S. , Sammons R. Douglas
Published: March 2018

Uptake and translocation of glyphosate in three commercial formulations were examined in velvetleaf, a dicotyledonous weed that is commonly treated with glyphosate. The formulations included Roundup®(MON 35085), Roundup Ultra, and Touchdown®as sold in Canada. A minimal amount of14C-glyphosate was spiked into a lethal rate of each formulation, and the short-term (3 to 72 h) uptake into the treated leaf and subsequent translocation into the plant were measured. Time-course studies showed very rapid uptake and translocation of glyphosate in the Ultra formulation. In comparison, the uptake and translocation of glyphosate in Touchdown was much slower but continued throughout the 72-h period. Glyphosate in the Roundup formulation showed intermediate uptake and translocation. Tissue necrosis at the application sites of Ultra and Roundup was visible within 24 h after treatment. Examinations using stereo and fluorescence microscopy revealed extensive cell death and tissue disruption. Tissue necrosis from Ultra and Roundup was also observed in blank formulations containing no glyphosate and therefore was likely caused by the surfactants. In contrast, the application sites of Touchdown produced little to no leaf damage. Our results demonstrated a direct correlation between tissue necrosis and rapid rates of glyphosate uptake and translocation.
Herbicide Efficacy on FourAmaranthusSpecies in Soybean (Glycine max)
Authors: Sweat Jonathan K. , Horak Michael J. , Peterson Dallas E. , Lloyd Randy W. , Boyer John E.
Published: March 2018

Field and greenhouse studies were conducted in 1995 and 1996 in Kansas to determine the efficacy of 21 herbicide treatments for control of tumble pigweed, Palmer amaranth, redroot pigweed, and two biotypes of common waterhemp in soybean. In field studies, nine of eleven preemergence treatments controlled all four species 90% or more. However, pendimethalin and trifluralin controlled Palmer amaranth, redroot pigweed, and tumble pigweed less than the other preplant incorporated and preemergence treatments. With the exception of flumiclorac and NAF-75, postemergence treatments controlled 75 to 90% of all four species. A biotype of common waterhemp collected in Iowa was not controlled by acetolactate synthase-inhibiting herbicides. Greenhouse results were similar to field experiments. Results suggest at least 90% control of theseAmaranthusspecies is possible with proper herbicide selection.
Impact, Biology, and Ecology of Saltcedar (Tamarixspp.) in the Southwestern United States
Authors: Di Tomaso Joseph M.
Published: March 2018

Eight species ofTamarixwere first brought to North America in the 1800s from southern Europe or the eastern Mediterranean region. Many of the species escaped cultivation and by the 1920s invaded about 4,000 ha of riparian habitat in the southwestern United States. By 1987, it was estimated to have increased to at least 600,000 ha. The success of saltcedar in the southwest can be attributed to several factors related to its growth habit, reproduction, water usage, ability to tolerate highly saline conditions, and redistribution of salt from deep in the soil profile to the soil surface. The flowers produce small, numerous, and tufted seeds that can be carried long distances by wind or water. The seeds, however, have a short period of viability, and must come in contact with suitable moisture within a few weeks of dispersal. Unlike obligate phreatophytes, such as willows and cottonwoods, saltcedar is a facultative phreatophyte and is often able to survive under conditions where groundwater is inaccessible. The high evapotranspiration rates of saltcedar can lower the water table and alter the floristic composition in heavily infested areas. Mature plants are tolerant to a variety of stress conditions, including heat, cold, drought, flooding, and high salinity. Saltcedar is not an obligate halophyte but survives in areas where groundwater concentrations of dissolved solids can average 8,000 ppm or higher. In addition, the leaves of saltcedar excrete salts that are deposited on the soil surface under the plant, inhibiting germination and growth of competing species.
Saltcedar (Tamarixspp.) Management with Imazapyr
Authors: Duncan Keith W. , McDaniel Kirk C.
Published: March 2018

During the 20th century, naturalized saltcedar has become common within major tributaries throughout the western United States. Often growing in nearly monocultural stands, saltcedar is suspected of lowering water tables, thus destroying wetlands and wildlife habitats. Management efforts have primarily relied on mechanical and cultural practices, but recent success in controlling saltcedar with imazapyr has led to wider herbicide use. Based on a number of research/extension field trials in New Mexico from 1987 to present, imazapyr applied alone or in combination with glyphosate was found to control saltcedar to levels of 90% or greater, especially when applied in August or September. For fixed-wing aircraft applications, we recommend applying imazapyr at 1.1 kg ai/ha or imazapyr plus glyphosate at 0.56 plus 0.56 kg/ha. For individual plant treatments, we recommend spraying the foliage to wet with imazapyr at 1% v/v in water, or imazapyr plus glyphosate at 0.5 plus 0.5% v/v. Herbicide activity may be reduced as saltcedar height and stem number increases.
A Systems Approach for the Management of Russian Knapweed (Centaurea repens)
Authors: Bottoms Rick M. , Whitson Tom D.
Published: March 2018

Studies were initiated in Wyoming to determine the potential of grass competition as an alternative to repetitive herbicide treatment or other cultural practices for control of Russian knapweed. An experiment was established to evaluate the effects of five grass species, including Russian wildrye cv. ‘Bozoisky.’ Picloram, applied to Russian knapweed during the first frost, reduced Russian knapweed from an average of 80.1% live canopy cover which equates to 0% control. Untreated, unseeded checks resulted in 83.9 and 81.1% control in tilled and nontilled treated plots, respectively. Grass cover increased in untreated seeded plots from an average of 11.3 and 8.2% in tilled and nontilled plots, respectively, to 65% in tilled and 66% in nontilled plots treated with clopyralid plus 2,4-D. Grass cover also increased 69.7% in tilled and 66% in nontilled plots treated with picloram. There was no significant difference between grass varieties when compared to percent Russian knapweed cover. Reductions to zero live canopy cover of Russian knapweed were obtained with a single application of picloram. Economic feasibility thresholds were obtained from four out of five varieties, including a significant difference provided by nontilled Russian wildrye treated with picloram.
Leafy Spurge (Euphorbia esula) Control with Several Grass Species
Authors: Ferrell Mark A. , Whitson Thomas D. , Koch David W. , Gade A. E.
Published: March 2018

Studies were established near Devil's Tower in Crook County, WY, to determine the potential of 11 grass species to compete with leafy spurge as an alternative to repetitive herbicide treatments. Of the 11 species, ‘Bozoisky’ Russian wildrye and ‘Luna’ pubescent wheatgrass showed the most promise for successful competition with leafy spurge and were selected for further study. Pubescent wheatgrass limited percent canopy cover of leafy spurge to 10 and 15% or less in tilled and no-till plots, respectively, 7 and 10 yr after seeding. Russian wildrye limited percent canopy cover of leafy spurge to 21% or less in tilled and 7 and 27% in the no-till plots, respectively, 7 or 10 yr after seeding. The control plots not seeded to a forage grass averaged 55% leafy spurge canopy cover.
Weed Control in Potato (Solanum tuberosum) with Rimsulfuron and Metribuzin
Authors: Renner Karen A. , Powell Gary E.
Published: March 2018

Field studies were conducted for 3 yr to determine weed and potato response to preemergence (PRE) and postemergence (POST) applications of rimsulfuron, metribuzin, and rimsulfuron plus metribuzin. Preemergence applications of rimsulfuron at 27 g ai/ha and POST applications at 18 g/ha controlled barnyardgrass, redroot pigweed, and wild buckwheat. Common lambsquarters was controlled by PRE or POST applications of metribuzin or a tank mixture of 18 g/ha rimsulfuron plus 140 g ai/ha of metribuzin. ‘Russet Burbank’ potato was relatively tolerant to all rimsulfuron, metribuzin, and rimsulfuron plus metribuzin applications, and potato yield was not reduced compared to the hand-weeded control.
Wetland Nightshade (Solanum tampicense): A Threat to Wetlands in the United States
Authors: Fox Alison M. , Bryson Charles T.
Published: March 2018

Wetland nightshade (WNS) (Solanum tampicense Dunal) is a member of the family Solanaceae. In some texts, WNS has been referred to as Solanum houstonii Dunal, but this homonym of the 1807 S. houstonii Martyn is illegitimate according to the International Code for Botanical Nomenclature (Wunderlin et al. 1993). WNS is thought to have originated in southern Mexico, the West Indies, Guatemala, Belize (Gentry and Standley 1974), Cuba, and El Salvador (Standley 1924). It was first reported from mainland Florida in a marsh south of Punta Gorda, Charlotte County, in 1983 (Wunderlin et al. 1993). Since that time, it has been detected in Florida in Highlands (1985), DeSoto (1991), Lee (1995), and Glades (1996) counties. Recently, WNS was rediscovered on Garden Key in the Dry Tortugas (110 km west of Key West) where it was growing in a moist seep area within the partially ruined Small Magazine in Fort Jefferson. This species has been included in the plant list of the Dry Tortugas National Park since 1974 (Reimus and Robertson 1995).