bluuebunny/crossref_metadata_2025 huggingface dataset:
Carrot (Daucus carota) and Weed Response to Linuron and Metribuzin Applied at Different Crop Stages
Authors: Bellinder Robin R. , Kirkwyland Jonathan J. , Wallace Russell W.
Published: March 2018

Redroot pigweed and common lambsquarters control was variable within and between seasons when postemergence linuron and metribuzin were applied one or two times at below-labeled rates to one-, three-, or five-leaf carrots. A single, low-rate application of either herbicide at the one-or three-leaf stage of carrots failed to provide adequate season-long broadleaf weed control. Two low-rate applications to either one- + three- or three- + five-leaf carrots significantly improved control. Linuron produced little or no injury to carrots regardless of application timing. Metribuzininduced injury was variable initially and decreased to 10% or less by 14 d after treatment. One application of either linuron or metribuzin resulted in reduced yields of carrots.
Control of Sulfonylurea-Resistant Kochia (Kochia scoparia)
Authors: Tonks Dennis J. , Westra Philip
Published: March 2018

Greenhouse and field experiments were conducted to assess the effectiveness of herbicide tank mixtures for control of sulfonylurea (SU)-resistant and -susceptible kochia biotypes. Kochia control at three growth stages was evaluated for fluroxypyr, dicamba, 2,4-D, bromoxynil, and bromoxynil plus MCPA. Control decreased as kochia size increased, especially at less than full labeled herbicide rates. Treatments containing bromoxynil provided best overall control in the greenhouse but were less effective on larger kochia plants in the field. Dicamba and fluroxypyr provided similar, effective kochia control both in greenhouse and field experiments. 2,4-D did not provide acceptable kochia control regardless of formulation, rate, or application timing. All kochia biotypes responded similarly to non-SU herbicides. In the field, inclusion of an SU herbicide in the treatment generally resulted in no increased R-kochia control above that provided by the non-SU herbicide. R-kochia population dynamics can affect selection of alternative control strategies.
Influence of Emulsifiable Oils and Emulsifier on the Performance of Phenmedipham, Metoxuron, Sethoxydim, and Quizalofop
Authors: De Ruiter Hans , Uffing Andre J. M. , Meinen Esther
Published: March 2018

Field and growth chamber experiments were conducted to investigate the influence of emulsifiable mineral oil, emulsifiable rapeseed oil, and the emulsifier (polyoxyethylene C13/C15oxo alcohol) on the efficacy of phenmedipham and metoxuron against common lambsquarters, and of sethoxydim and the ethyl ester of quizalofop against winter wheat. In field studies, mineral oil and rapeseed oil were equally effective in increasing the efficacy of phenmedipham (0.24 and 0.48 kg ai/ha), metoxuron (0.6 and 1.2 kg ai/ha), and sethoxydim (0.05 and 0.1 kg ai/ha), but mineral oil was superior to rapeseed oil with quizalofop. In growth chamber studies, mineral oil and rapeseed oil were equally effective in increasing the efficacy of metoxuron, sethoxydim, and quizalofop-ethyl, but rapeseed oil was more effective than mineral oil with phenmedipham. Both in the field and in the growth chamber, the emulsifier was at least as effective as the oil adjuvants, when combined with all herbicides except sethoxydim. The herbicide doses giving 50% response (ED50) were determined for the growth chamber experiments. The adjuvants reduced the ED502.7-fold with phenmedipham, 51-fold with metoxuron, 2.7-fold with sethoxydim, and 6.8-fold with quizalofop when averaged over the three adjuvants. It was concluded that rapeseed oil (all tested herbicides except quizalofop) or the emulsifier (all tested herbicides except sethoxydim) can serve as a substitute for mineral oil.
Economics and Efficacy of Postemergence Spurred Anoda (Anoda cristata) Control in Pinto Beans (Phaseolus vulgaris)
Authors: Vangessel Mark J. , Westra Phil
Published: March 2018

Spurred anoda is an increasing weed problem in Colorado pinto bean production. This research was designed to evaluate reduced rates of bentazon and imazethapyr applied at various times for spurred anoda control and profitability. In 1993, spurred anoda control with early applications of either bentazon or imazethapyr was superior to late applications. Bentazon provided better spurred anoda control than imazethapyr in June. Spurred anoda control in 1993 was better than in 1994 due to late-emerging weeds and herbicide treatments not providing residual control. In 1994, bentazon controlled spurred anoda better than imazethapyr 1 and 3 wk after late POST, but no treatment provided commercially acceptable full-season control. The number of treatments with gross margins greater than the untreated check increased as pinto bean prices increased, but ranking of gross margin did not change due to pinto bean prices.
Influence of Application Variables on Efficacy of Glyphosate
Authors: Jordan David L. , York Alan C. , Griffin James L. , Clay Patrick A. , Vidrine P. Roy , Reynolds Daniel B.
Published: March 2018

Field experiments were conducted from 1993 to 1995 to compare weed control by the isopropylamine salt of glyphosate at 0.21, 0.42, 0.63, and 0.84 kg ae/ha applied at three stages of weed growth. Weed control by glyphosate applied at these rates alone or with ammonium sulfate at 2.8 kg/ha was also evaluated. In other experiments, potential interactions between glyphosate and acifluorfen, chlorimuron, and 2,4-DB were evaluated. Velvetleaf, prickly sida, sicklepod, pitted morningglory, entireleaf morningglory, palmleaf morningglory, and hemp sesbania were controlled more easily when weeds had one to three leaves compared with control when weeds had four or more leaves. Glyphosate controlled redroot pigweed, velvetleaf, prickly sida, sicklepod, and barnyardgrass more effectively than pitted morningglory, entireleaf morningglory, palmleaf morningglory, or hemp sesbania. Increasing the rate of glyphosate increased control, especially when glyphosate was applied to larger weeds. Greater variation in control was noted for pitted morningglory, palmleaf morningglory, prickly sida, and velvetleaf than for redroot pigweed, sicklepod, entireleaf morningglory, or hemp sesbania. Ammonium sulfate increased prickly sida and entireleaf morningglory control but did not influence sicklepod, hemp sesbania, or barnyardgrass control. Acifluorfen applied 3 d before glyphosate or in a mixture with glyphosate reduced barnyardgrass control compared with glyphosate applied alone. Chlorimuron did not reduce efficacy. Mixtures of glyphosate and 2,4-DB controlled sicklepod, entireleaf morningglory, and barnyardgrass similar to glyphosate alone.
The Persistence of Trifluralin Resistance in Green Foxtail (Setaria viridis) Populations
Authors: Andrews Todd S. , Morrison Ian N.
Published: March 2018

In the summer of 1995, green foxtail seed samples were collected from 17 fields in southwestern Manitoba where trifluralin resistance was first identified in 1988. Since 1988, six of these fields had not been treated with dinitroaniline herbicides (DNAHs), four had been treated once, and seven had been treated two or more times. The proportions of resistant (R) and susceptible (S) seeds in each sample were determined using a petri-dish seed bioassay. Among the samples collected from fields that had not been treated between 1988 and 1995, two contained > 99% R seeds. The others ranged from 40 to 83%. Among the four samples collected from fields that were treated once, two contained > 99% R seeds and the other two contained 59 and 67% R seeds. Five of the seven samples collected from fields treated two or more times contained > 97% R seeds and the other two approximately 89 and 68% resistant seeds. There was no statistical correlation between the proportion of R seeds and the frequency of DNAH use since 1988. The proportion of R seeds present in 1988 and 1995 could not be compared because of the way in which fields were treated prior to sampling in the 2 yr; however, the results clearly indicate that trifluralin resistance can persist in green foxtail populations for at least 7 yr. By inference, the results indicate that trifluralin-resistant green foxtail plants are almost, if not equally, as fit as susceptible plants. Consequently, once resistance is present in a green foxtail population, DNAHs cannot be used for its control, even in the absence of additional selection pressure, for at least 7 yr and probably much longer.
Quackgrass (Elytrigia repens) Control in Corn (Zea mays) with Nicosulfuron and Primisulfuron
Authors: Bruce Joseph A. , Kells James J.
Published: March 2018

Quackgrass is a serious weed problem in the northern United States and southern Canada. Field experiments were conducted in 1990 and 1991 to examine the effect of herbicide rate, application timing, quackgrass growth stage, and cultivation on quackgrass control with nicosulfuron and primisulfuron in corn. Nicosulfuron (35 g ai/ha) and primisulfuron (40 g ai/ha) each provided 84% or greater control of two-leaf plants and 93% or greater control of four-leaf quackgrass plants. Sequential applications of both nicosulfuron and primisulfuron provided greater season-long control than single applications of the same rate on two-leaf but not four-leaf quackgrass. Cultivation 10 d after nicosulfuron or primisulfuron application often increased early-season control, but by corn harvest few differences were observed. Postemergence (POST) applications of nicosulfuron and primisulfuron provided at least 88% control, compared with 66 to 86% from an early preplant application of glyphosate. Corn yields were similar regardless of the quackgrass control program.
Classification of Herbicides by Site of Action for Weed Resistance Management Strategies
Authors: Retzinger E. James , Mallory-Smith Carol
Published: March 2018

A classification of herbicides according to their sites of action was developed to help maintain the usefulness of herbicides as a tool in crop production to delay the selection of herbicide-resistant weeds. The classification includes a numbering system for the site of action, the chemical family, and the common name of the herbicide. The United States of America trade name and package mixes also are included.
Glufosinate-Resistant, BAR-Transformed Rice (Oryza sativa) and Red Rice (Oryza sativa) Response to Glufosinate Alone and in Mixtures
Authors: Sankula Sujatha , Braverman Michael P. , Linscombe Steven D.
Published: March 2018

Glufosinate applied postemergence alone and in mixture with pendimethalin, thiobencarb, quinclorac, propanil, bensulfuron, bentazon, acifluorfen, or triclopyr was evaluated on bialaphosresistant (BAR) rice and red rice in field studies. Glufosinate at 2.2 kg ai/ha alone was less phytotoxic (6%) to BAR-transformed rice than when it was applied in combination with 0.4 kg ai/ha triclopyr (59%) or 0.6 kg ai/ha acifluorfen (22%). Rice yield with glufosinate alone was similar to the weed-free check the first year, but 13% less than the weed-free check the second year. For the glufosinate plus triclopyr mixture, rice yield was reduced by 39 and 76% compared with glufosinate alone in 1994 and 1995, respectively. Red rice control was 92% with either 3.4 kg ai/ha propanil or 0.6 kg/ha acifluorfen mixed with 0.6 kg/ha glufosinate, which was greater than for glufosinate alone and the other combinations. Propanil or acifluorfen mixed with glufosinate reduced red rice plant height, panicle maturity, and 100-seed weight 16, 31, and 24%, respectively, compared to glufosinate alone and 30, 48, and 43%, respectively, compared to the nontreated weedy check.
Bermudagrass (Cynodon dactylon) Control in Sunflower (Helianthus annuus), Soybean (Glycine max), and Potato (Solanum tuberosum) with Postemergence Graminicides
Authors: Bedmar Francisco
Published: March 2018

Field experiments were conducted from 1989 to 1992 in Balcarce, Tandil, and San Cayetano, all in Buenos Aires province (Argentina), to evaluate clethodim, fenoxaprop-P-ethyl, fluazifop-P, haloxyfop, propaquizafop, and quizalofop-P-ethyl for bermudagrass control in sunflower, soybean, and potato. The highest levels of bermudagrass control 60 days after treatment (DAT) were generally obtained with fenoxaprop-P-ethyl, haloxyfop, propaquizafop, and quizalofop-P-ethyl. Late season bermudagrass control, based on biomass of stolons and rhizomes, suggested that the most consistent treatments in potato and sunflower were haloxyfop at 180 g ai/ha and quizalofop-P-ethyl at 54 g ai/ha. In soybean, clethodim at 336 g ai/ha, haloxyfop at 180 g/ha, propaquizafop at 100 g ai/ha, and quizalofop-P-ethyl at 54 g/ha provided the greatest reductions in bermudagrass biomass. All of the postemergence (POST) graminicide treatments increased crop yields when compared to a nontreated check. However, little or no difference in yield was obtained when herbicide rate was increased.
Sequential Applications of Preemergence and Postemergence Herbicides for Large Crabgrass (Digitaria sanguinalis) Control in Tall Fescue (Festuca arundinacea) Turf
Authors: Johnson B. Jack
Published: March 2018

Preemergence (PRE) and postemergence (POST) herbicides were sequentially applied to tall fescue over a 2-yr period to determine the lowest herbicide rates needed for acceptable large crabgrass control. Prodiamine was the only PRE herbicide that provided full-season large crabgrass control in tall fescue turf. The control was 85% in plots treated at one-third recommended rate (0.3 kg/ha) and 96% at the full rate (0.8 kg/ha). Sequential applications of oxadiazon at one-third recommended rate (1.1 kg/ha) in late February followed by fenoxaprop (0.2 kg/ha) in June controlled 85% large crabgrass in late August. Control was similar in mid-August when pendimethalin, dithiopyr, or oryzalin at one-third recommended rates was followed by fenoxaprop, but was not acceptable (≤ 74%) by late August. In most instances, large crabgrass control was higher when fenoxaprop followed the PRE herbicide application than with MSMA. Reduced herbicide rates may not provide full-season large crabgrass control in other areas with different soil and weather conditions. Tall fescue quality was not affected by prodiamine, dithiopyr, and oxadiazon. In 1996, pendimethalin at 3.3 kg/ha reduced turf quality 16% and oryzalin at 2.2 kg/ha reduced quality by 46%. In 1995, MSMA reduced the quality of tall fescue more (≤ 21%) than fenoxaprop (≤ 10%). When compared to the use of PRE and POST herbicides alone, sequential PRE plus POST herbicide programs did not affect turfgrass quality.
ALS-Inhibiting Herbicide Seed Treatments Control Striga hermonthica in ALS-Modified Corn (Zea mays)
Authors: Berner Dana K. , Ikie Felix O. , Green Jerry M.
Published: March 2018

Seed treatments with two acetolactate synthase (ALS)-inhibiting herbicides, the sulfonylurea herbicide nicosulfuron and the imidazolinone herbicide imazaquin, controlled the parasitic weed Striga hermonthica in corn. The XA-17 gene in ALS-modified P3180IR corn strongly reduced corn injury from herbicide seed treatments while another ALS modification was not effective. Combining seed treatment of ALS-inhibiting herbicides and ALS-modified corn with the XA-17 gene may offer a practical means for African growers to control Striga hermonthica.
Impact of Tyta luctuosa (Lepidoptera: Noctuidae) on Hedge Bindweed (Calystegia sepium) in Corn (Zea mays)
Authors: Tipping Philip W. , Campobasso Gaetano
Published: March 2018

Releasing Tyta luctuosa on hedge bindweed in cornfields did not increase defoliation more than endemic herbivores. Larvae of T. luctuosa were rarely found after release, indicating they suffered high mortality or dispersed from test plants. Eleven species of endemic insects were found feeding on bindweed, all of which are known to be generalists feeding, in some cases, on economically important plants. Oidaematophorus monodactylus (L.) (Lepidoptera: Pterophoridae) was the most damaging species to the bindweed.
Preemergence Weed Control in Potatoes (Solanum tuberosum) with Rimsulfuron Mixtures
Authors: Guttieri Mary J. , Eberlein Charlotte V.
Published: March 2018

Field studies were conducted to evaluate preemergence weed control in irrigated potatoes with rimsulfuron plus metribuzin or three-way mixtures of rimsulfuron plus metribuzin plus EPTC, metolachlor, or pendimethalin. Redroot pigweed control was ≥ 96% with rimsulfuron plus metribuzin at 18 g ai/ha + 140 g/ha, and common lambsquarters control was ≥ 97% with rimsulfuron plus metribuzin at 26 g/ha + 210 g/ha. Hairy nightshade control with rimsulfuron plus metribuzin ranged from 58 to 99%, and green foxtail control ranged from 50 to 98%. EPTC, metolachlor, or pendimethalin rates required for acceptable green foxtail and hairy nightshade control in combination with a given rate of rimsulfuron plus metribuzin varied with environmental conditions. Potato tuber yield generally improved with rimsulfuron plus metribuzin application.
Competitive Grasses for Leafy Spurge (Euphorbia esula) Reduction
Authors: Lym Rodney G. , Tober Dwight A.
Published: March 2018

Twelve grass genotypes were evaluated for competitiveness with leafy spurge and herbage yield in two sites in North Dakota. ‘Rebound’ smooth brome, ‘Rodan’ western wheatgrass, ‘Bozoisky’ Russian wildrye, and ‘Arthur’ Dahurian wildrye reduced leafy spurge stem density an average of 63% after 3 yr in a silty clay soil at Fargo. ‘Reliant’ intermediate wheatgrass reduced leafy spurge stem density every year for 3 yr, including an 85% reduction the second year after planting, and consistently produced high herbage yields. Rebound smooth brome and Reliant intermediate wheatgrass averaged 72% leafy spurge reduction 3 yr after seeding in a loamy sand soil at Jamestown. Reliant intermediate wheatgrass and ‘Manska’ pubescent wheatgrass provided the most consistent herbage production, which averaged about 2,000 kg/ha annually for 3 yr.
Genetic Analysis of Glufosinate Resistance in Crosses Between Transformed Rice (Oryza sativa) and Red Rice (Oryza sativa)
Authors: Sankula Sujatha , Braverman Michael P. , Oard James H.
Published: March 2018

Reciprocal controlled crosses were made in the greenhouse between Gulfmont rice transformed with the bialaphos resistance (BAR) gene and red rice and BAR-transformed Koshihikari rice and red rice to assess the inheritance of glufosinate resistance. All F1 plants were resistant to 2.2 kg ai/ha glufosinate. Ammonia accumulation as a measure of glufosinate resistance in the F1 hybrids was assayed at 4 and 8 days after treatment (DAT). Ammonia accumulation in hybrids 4 DAT was similar to glufosinate treated, transformed rice, while treated nontransformed plants accumulated 14 to 23 times more ammonia compared with the hybrids. The nature of inheritance of glufosinate resistance in F2 rice plants was studied by a glufosinate dip test, a spray test, and ammonia assay. All three tests confirmed that glufosinate resistance, as influenced by the BAR gene, segregated in a 3 (resistant): 1 (susceptible) ratio.
Tillage and Planting Date Influence Foxtail (Setariaspp.) Emergence in Continuous Spring Wheat (Triticum aestivum)
Authors: Spandl Eric , Durgan Beverly R. , Forcella Frank
Published: March 2018

Foxtail emergence patterns were evaluated in spring wheat under three tillage regimes, moldboard plow, chisel plow, and no-till, and three wheat planting dates. The first planting date was as soon as feasible in spring, and the second and third planting dates averaged 9 and 17 d later. Foxtail emergence patterns and seedbank density were evaluated each year for three consecutive years. Green foxtail was the dominant weed species. Tillage regime did not influence initial percent emergence of foxtail. Subsequent percent foxtail emergence was sometimes lower in no-till or chisel plow than in moldboard plow regimes until emergence approached 100%. By the third year, total foxtail plant emergence was greater in no-till and chisel plow than in moldboard plow and also greater in no-till than chisel plow. Earlier planting generally increased percent foxtail emergence until midseason. At 22 d after planting, average emergence of foxtail was 48, 67, and 81% for planting dates one, two, and three, respectively. Delayed planting increased rate of foxtail emergence but decreased density of emerged seedlings. Producers adopting chisel plow or no-till systems can expect to see greater foxtail infestations than in moldboard plow systems. Subsequently, more extensive weed management in reduced tillage systems will be needed to prevent heavy foxtail infestations. Delaying wheat planting may be a viable option for foxtail management through reduced plant densities and more simultaneous emergence patterns.
Seedling Emergence of Winter Annual Grasses as Affected by Limited Tillage and Crop Canopy
Authors: Anderson R. L.
Published: March 2018

Jointed goatgrass and downy brome continue to plague winter wheat producers in the western United States. Because there are no effective herbicides for in-crop control of these weeds, producers are seeking cultural practices that stimulate seed germination and deplete the soil seed bank. We determined the effect of limited tillage and crop canopy on seedling emergence of these grasses. One tillage operation with a sweep plow increased jointed goatgrass seedling emergence 74% in the first year but did not affect emergence in later years. Downy brome emergence was not affected by tillage. Jointed goatgrass seedlings emerged over 5 yr, whereas downy brome did not emerge after 3 yr. Seedling emergence of both species was two times greater in corn and barley than in proso millet. Producers will accrue more benefit for seedbank management with cultural strategies such as alternative rotations and competitive wheat canopies than with limited tillage using a sweep plow.
Postemergence Weed Control with CGA-277476 and Cloransulam-Methyl in Soybean (Glycine max)
Authors: Nelson Kelly A. , Renner Karen A.
Published: March 2018

Field and greenhouse experiments were conducted to evaluate postemergence (POST) soybean injury and weed control with CGA-277476 and cloransulam-methyl alone and in tank mixtures. In the field, visible soybean injury was 12 to 14% from CGA-277476 and 9 to 13% from cloransulam-methyl 7 d after treatment. Tank mixtures of either herbicide with acifluorfen or acifluorfen plus thifensulfuron were more injurious than CGA-277476 or cloransulam-methyl applied alone. Both CGA-277476 and cloransulam-methyl reduced velvetleaf dry weight 82%, and cloransulam-methyl reduced common ragweed dry weight 92%. Neither herbicide adequately controlled common lambsquarters, redroot pigweed, nor eastern black nightshade. The addition of acifluorfen to the spray solution improved common ragweed, common lambsquarters, redroot pigweed, and eastern black nightshade control with CGA-277476 and improved common lambsquarters, redroot pigweed, and eastern black nightshade control with cloransulam-methyl. Tank mixing thifensulfuron with CGA-277476 or cloransulam-methyl increased common lambsquarters and redroot pigweed control. In the greenhouse, CGA-277476 at 20 g ai/ha reduced velvetleaf dry weight 98%, and 79 g/ha was required to reduce common ragweed dry weight 93%. Cloransulam-methyl at 4.4 g ai/ha reduced velvetleaf dry weight 98% and common ragweed dry weight 94% at 8.8 g/ha. Chlorimuron reduced yellow nutsedge dry weight more than CGA-277476 or cloransulam-methyl. Antagonism of POST graminicide activity by CGA-277476 was grass species and graminicide related. CGA-277476 reduced giant foxtail control by clethodim but not by quizalofop. Cloransulam-methyl tank mixed with clethodim or quizalofop controlled giant foxtail.
Sensor-Controlled Hooded Sprayer for Row Crops
Authors: Hanks James E. , Beck James L.
Published: March 2018

Methods were developed and evaluated that utilize state of the art weed-sensing technology in row-crop production systems. Spectral differences in green living plants and bare soil allowed ‘real-time’ weed detection, with intermittent spraying of herbicide only where weeds were present. Sensor units were mounted in 0.7-m-wide hooded sprayers providing sensors with an unobstructed view of the area between soybean rows. Single hood and commercial-size eight-row systems were evaluated, and savings in glyphosate spray solution applied using sensors ranged from 63 to 85%, compared to conventional hooded spray systems with continuous application. Weed control by the sensor-controlled spray system was equal to the conventional system. This technology can significantly reduce herbicide usage and decrease production cost without reducing weed control.
Bromoxynil-Resistant Common Groundsel (Senecio vulgaris)
Authors: Mallory-Smith Carol
Published: March 2018

Resistance to bromoxynil and terbacil was confirmed in common groundsel collected from peppermint (Mentha piperita) fields in Oregon. This is the first reported case of a bromoxynil-resistant weed selected under field conditions. The bromoxynil rate required to reduce growth by 50% was 10 times higher for the resistant biotype than for the susceptible biotype. The bromoxynil-resistant biotype also was resistant to terbacil.
Restoration of Saltcedar (Tamarix spp.)-Infested Floodplains on the Bosque del Apache National Wildlife Refuge
Authors: Taylor John P. , McDaniel Kirk C.
Published: March 2018

Vegetation development bordering the Middle Rio Grande, as with most major southwestern U.S. tributaries, has historically undergone rapid and dynamic change. The introduction of saltcedar (or Tamarisk, genus Tamarix) and other exotic species into this environment within the 20th century has contributed to this process. These plants are now an integral component of the riparian vegetation mix. Manpower, logistics, and financial resources constrain the degree to which a desired riparian habitat can be restored from saltcedar thickets on the Bosque del Apache National Wildlife Refuge near Socorro, NM. Saltcedar clearing is accomplished using a combination of herbicide, burning, and mechanical control techniques costing from $750 to $1,300/ha. Soil salinity and depth to water are the principal physical features limiting revegetation efforts. Cottonwood and black willow plantings and natural regeneration after timed irrigations have produced diverse habitats that support a wide array of faunal species in areas previously occupied by homogeneous saltcedar.
The Biology and Management of Purple Loosestrife (Lythrum salicaria)
Authors: Mullin Barbra H.
Published: March 2018

Purple loosestrife is an invasive, introduced plant that is usually associated with wetland, marshy, or riparian sites. It is found across the northern tier states and provinces in North America. Purple loosestrife affects the diversity of native wetland ecosystems. Infestations lead to severe wildlife habitat degradation, loss of species diversity, and displacement of wildlife-supporting native vegetation, such as cattails and bulrushes. The plant spreads effectively along waterways, and the thick, matted root system can rapidly clog irrigation ditches, resulting in decreased water flow and increased maintenance. Effective management of purple loosestrife along waterways and in riparian areas requires integrating management strategies to prevent further introductions, detecting and eradicating new infestations, and containing and controlling large-scale infestations. Management practices that aid in the control of purple loosestrife include herbicide, physical, and biological practices. Each infestation site should be individually evaluated to determine the appropriate control measure. Factors to be considered include the proximity and type of vegetation on the site, whether the water is flowing or still, and the utilization of the site and the water (domestic, irrigation, recreation, or scenic value).
Control of Downy Brome (Bromus tectorum) in Winter Wheat (Triticum aestivum) with MON 37500
Authors: Blackshaw Robert E. , Hamman William M.
Published: March 2018

Field experiments were conducted to determine suitable application timings and rates of MON 37500 for downy brome control in winter wheat. MON 37500 applied preemergence (PRE) or in fall postemergence (POST) provided better control of downy brome than when applied spring POST. MON 37500 at rates ranging from 19 to 33 g ai/ha applied PRE or fall POST controlled downy brome >85%. MON 37500 applied spring POST at 60 g/ha only suppressed growth of downy brome. Winter wheat was not visibly injured and maturity was not delayed by MON 37500 applied up to 60 g/ha at any of the application timings. Winter wheat yield responded positively to all MON 37500 treatments but PRE or fall POST applications usually resulted in greater yields than spring POST applications. Wheat yields progressively increased with increasing rates of MON 37500 up to 30–40 g/ha, above which yields tended to plateau or, in two instances, decline slightly. MON 37500 is an important new herbicide that should enable growers to better manage downy brome in winter wheat production systems.
Validation of an Operator-Assisted Module to Measure Weed and Crop Leaf Cover by Digital Image Analysis
Authors: Ngouajio Mathieu , Lemieux Claudel , Fortier Jean-Jacques , Careau Denis , Leroux Gilles D.
Published: March 2018

The practical application of yield loss prediction models using relative leaf area of weeds is limited due to the lack of a quick and accurate method of leaf area estimation. Leaf cover (the vertical projection of plant canopy on the ground) can be used to approximate leaf area at early stages of plant development. An automated digital image analysis system for measuring leaf cover has been developed. The system has an operator-assisted module aimed at validating the automated functions. The objective of this research was to demonstrate the accuracy of the operator-assisted module under different weed–crop conditions. A laboratory experiment was conducted using simulated weed–crop populations. Two additional field experiments were conducted using corn in competition with: (1) common lambsquarters, barnyardgrass, or a mixture of both species, and (2) a natural weed community. In the laboratory experiment, a narrow linear relation was observed between leaf cover estimated with the operator-assisted module and leaf area measured with an optical area meter (r2> 0.98). In field experiments, the regression between corn leaf cover estimated by the operator-assisted module and corn leaf area measured with the optical area meter was not as good (r2< 0.55). The poor performance of the module was probably due to the overlapping and the architecture of corn leaves (especially unexpanded leaves). Nevertheless, the system showed high precision in estimating leaf area of both grassy weeds and broadleaf weeds (r2> 0.89). Generally, the accuracy of the estimates decreased as the growth stage became more advanced. Apart from its initial purpose as a calibration tool for the automated system, the operator-assisted module can have several potential research applications. It can be used: (1) as an alternative to destructive leaf area measurement at early stages of plant development, (2) as a tool in the study of plant competitive ability, and (3) as an objective and quantitative support to visual observations.
Management of Blackgrass (Alopecurus myosuroides) in Winter Wheat in Greece
Authors: Vizantinopoulos S. , Katranis N.
Published: March 2018

Field experiments were carried out from 1987 to 1990 to develop an integrated weed control management system for the control of blackgrass in winter wheat in Greece. The weed control treatments included both herbicides and cultural measures. The performance of preemergence (PRE) herbicides against blackgrass was better than postemergence (POST) herbicides; selectivity was dependent on application rate. Late timing of wheat sowing resulted in significant reduction of the blackgrass population competing with wheat. The critical period for blackgrass infestation occurred 4.0 to 5.5 wk after wheat emergence. Blackgrass density of 170 to 1,170 plants/m2caused wheat yield reduction equal to 10 and 30%, respectively. A quadratic relationship describing the percent reduction of wheat yield due to competition with different blackgrass densities was developed. The economic threshold level for blackgrass varied between 100 and 125 plants/m2. The results emphasize the importance of using a combination of chemical and cultural controls, including critical periods for herbicide application in maintaining an integrated approach for blackgrass control in wheat.
Comparison of Purple Nutsedge (Cyperus rotundus) from Around the World
Authors: Wills Gene D.
Published: March 2018

Purple nutsedge collections from 13 states within the continental United States and from 21 other locations around the world were studied to compare their reproduction and morphological characteristics. Differences occurred in the number of shoots produced from single tubers, the number of leaves per shoot, and the length and width of leaves. Differences were also found with respect to flowering, length of culms supporting the inflorescences, and number, length, and width of involucral bracts at the apex of the culms. Variations occurred in the flower parts, including the number and length of rachises and the length of rachillae and spikelets. There were differences in the growth patterns of the leaves, with some collections having leaves mostly erect and others having leaves lie more closely to the ground. The color of the leaves varied between light and dark green, and the color of the inflorescence varied between light and dark purplish-brown. Greater variation was found among plants from different locations around the world than from within the continental United States.
Red Rice (Oryza sativa) Control and Seedhead Reduction with Glyphosate
Authors: Askew Shawn D. , Shaw David R. , Street Joe E.
Published: March 2018

Glyphosate was evaluated at 0.8, 1.3, and 1.7 kg ae/ha applied at the two-leaf, four-leaf, or two- to three-tiller growth stage for red rice control. In addition, red rice seedheads were counted concurrently with soybean harvest at each of three locations to assess treatment effect on seedhead reduction. Field studies were conducted at Starkville, MS, in 1994 and 1995 and Shaw, MS, in 1995. A significant rate response was not observed for red rice control 2 and 4 wk after treatment (WAT) or for seedhead reductions. Glyphosate controlled red rice 88, 91, and 88% 2 WAT when applied to two-leaf, four-leaf, or two- to three-tiller red rice, respectively. Due to subsequent seedling emergence, control from glyphosate applications to two- or four-leaf red rice 4 WAT was 51 and 84%, respectively. Red rice treated at the two- to three-tiller stage was controlled 91% 4 WAT. When compared to the nontreated control, seedheads were reduced 97% by two- to three-tiller applications, compared to 87 and 56% reductions from four- and two-leaf applications, respectively.
Rapid Determination of Glyphosate Injury to Plants and Identification of Glyphosate-Resistant Plants
Authors: Singh Bijay K. , Shaner Dale L.
Published: March 2018

Drift of glyphosate may cause injury to nontarget plant species. Herbicidal damage caused by glyphosate may be attributed to the herbicides that inhibit acetohydroxyacid synthase (AHAS) or acetyl CoA carboxylase (ACCase), because the time taken to show herbicidal damage and the visual injury symptoms caused by these three types of herbicides are similar. Glyphosate inhibits the biosynthesis of aromatic amino acid biosynthesis which causes accumulation of shikimate in plants. A modified, simpler method of extraction and assay for detection of shikimate in plants has been adapted from previously published procedures. With this assay, rapid accumulation of shikimate was observed in glyphosate-sensitive plants that have been treated with glyphosate. Furthermore, the accumulation of shikimate in herbicide-sensitive plants was only due to glyphosate and not due to an AHAS or an ACCase inhibitor. Therefore, high levels of shikimate in a damaged plant indicate glyphosate injury. With this assay, no accumulation of shikimate was seen in a glyphosate-resistant variety of soybean. Therefore, lack of accumulation of shikimate in a glyphosate-treated weed or crop species indicates that the plant is resistant to glyphosate.
Weed Community and Species Response to Crop Rotation, Tillage, and Nitrogen Fertility
Authors: Anderson Randy L. , Tanaka Don L. , Black Al L. , Schweizer Edward E.
Published: March 2018

Producers in the northern Great Plains are exploring alternative crop rotations, with the goal of replacing spring wheat-fallow. We characterized the weed associations occurring with tillage system and nitrogen level in two rotations, spring wheat (SW)-fallow (F) and SW-winter wheat (WW)-sunflower (SUN). Weed density was measured 10 yr after initiation of the study. With both rotations, weed community density was highest with no-till. For SW-F, green foxtail, yellow foxtail, and fairy candelabra comprised 99% of the weed community, whereas 13 species were observed in SW-WW-SUN. Fairy candelabra, a rangeland species, was observed only in the no-till system of SW-F. In SW-WW-SUN, no-till favored kochia, Russian thistle, and foxtails, whereas common lambsquarters and annual sowthistle were more common in tilled systems. Nitrogen fertilizer increased crop competitiveness in SW-WW-SUN with no-till, subsequently reducing weed density. Cultural strategies that disrupt weed associations will aid producers in managing weeds.
Pale Smartweed (Polygonum lapathifolium L.) and Other Polygonums
Authors: Mitich Larry W.
Published: March 2018

The name Polygonum is a very ancient derivative, composed of the two Greek words, polys, many, and gony, knee or joint, alluding to the numerous and conspicuous nodes in the stems of many species. The Greek physician Heraclides Tarentina (third and second centuries BC) prescribed prostrate knotweed, P. aviculare L., as a remedy against bleeding from the ear. Dioscorides, a Greek botanist, was the first to characterize Polygonum as having “numerous slender branches, creeping on the ground like grass, with fruit at each leaf.” Subsequently, other Greek physicians, poets, and botanists applied the name to the knotweed/smartweed group, and in 1753, Linneaus adopted it for the genus. The species name for pale smartweed, lapathifolium, is from lapathi, meaning sorrel-like or dock-like (Gledhill 1985; Hyam and Pankhurst 1995; Small 1895).
Characterization of Imidazolinone-Resistant Smooth Pigweed (Amaranthus hybridus)
Authors: Manley Brian S. , Wilson Henry P. , Hines Thomas E.
Published: March 2018

Following six consecutive annual applications of imazaquin in combination with trifluralin or pendimethalin to several soybean fields on the Delmarva Peninsula, unacceptable smooth pigweed control was observed. Field and greenhouse studies were conducted to determine if this population of smooth pigweed was resistant to imazaquin and other herbicides. In field research, imazaquin and imazethapyr gave complete control of the susceptible (S) population while providing no control of the resistant (R) population; pyrithiobac controlled 99 and 90% of the R and S populations, respectively. Pendimethalin, metribuzin, MON-12000, and flumiclorac gave less than 75% control of both S and R populations. Chlorimuron, primisulfuron, CGA-152005, and lactofen gave above 75% control, and thifensulfuron and nicosulfuron gave above 90% control of both S and R populations. Seeds were collected from the R and S smooth pigweed populations for research in the greenhouse. Greenhouse studies confirmed high levels of resistance to imazaquin and imazethapyr and low levels of cross-resistance to rimsulfuron and chlorimuron in the R population. Susceptibility of the R population to nicosulfuron, thifensulfuron, pyrithiobac, and pendimethalin was comparable to that of the S population.
Redstem Filaree (Erodium cicutarium) Development and Productivity Under Noncompetitive Conditions
Authors: Blackshaw Robert E. , Harker K. Neil
Published: March 2018

Redstem filaree is becoming widespread and abundant on the Canadian prairies. A field study was conducted to determine the growth, development, and seed yield response of redstem filaree when grown under noncropped conditions and planted at various dates throughout the growing season in Alberta. Redstem filaree emerged within 7 to 13 d of planting with an accumulated 57 to 134 growing degree days (GDD). Flowering occurred within 46 to 65 d (327 to 779 GDD) of planting. Plants that emerged in August or later did not flower in that season and survived as winter annuals. Spring-emerging redstem filaree plants matured within 79 to 100 d (729 to 1,193 GDD). Plants that emerged in May and June attained more biomass and produced threefold more seeds than plants that emerged in July or later. Redstem filaree seed production ranged from 2,400 to 9,900 seeds/plant depending on emergence date and environmental conditions. Information from this study will assist in developing integrated management strategies for this increasingly important weed.
Johnsongrass (Sorghum halepense) Control and Rainfastness with Glyphosate and Adjuvants
Authors: Miller Donnie K. , Griffin James L. , Richard Edward P.
Published: March 2018

Glyphosate and adjuvant combinations were applied to rhizome johnsongrass at vegetative and reproductive growth stages to evaluate control and rainfastness in field studies. Using a rainfall simulator delivering 1.3 cm of water in 15 min, plots received either no rainfall or rainfall 15 or 60 min after glyphosate was applied at 2.1 kg ai/ha in combination with the nonionic surfactants Kinetic®HV at 0.25% (v/v) or Induce®at 1.0% (v/v) or the silicone surfactant Break-Thru®at 0.125% (v/v). Regardless of adjuvant, rainfall 15 or 60 min after application reduced johnsongrass control compared with no rainfall. Johnsongrass control 14 d after treatment at the reproductive stage was at least 89% with no rainfall, but no more than 53 and 65% with rainfall at 15 and 60 min, respectively. Based on initial weed control, adjuvants did not consistently improve rainfastness. Johnsongrass regrowth did not occur when glyphosate was applied with either adjuvant. In contrast, for glyphosate applied to johnsongrass in the vegetative stage, addition of Break-Thru improved control over Induce at both 15- and 60-min rainfall timings in one of two experiments. With no rainfall, addition of Kinetic HV and Break-Thru increased johnsongrass control in only one experiment. For application at the vegetative stage, johnsongrass regrowth averaged across rainfall timings was no more than 10%. In other field experiments, glyphosate at 1.4 kg/ha plus nonionic surfactants, silicone surfactant, crop oil concentrate, methylated seed oil, or a blend of silicone surfactant and methylated seed oil were equally effective in reducing johnsongrass regrowth when applied after seedhead emergence. Improved control of vegetative johnsongrass with some adjuvants was not reflected in decreased regrowth.
Hemp Dogbane (Apocynum cannabinum) Control in Corn (Zea mays) with Selective Postemergence Herbicides
Authors: Ransom Corey V. , Kells James J.
Published: March 2018

Field studies were conducted from 1994 to 1996 in Michigan to evaluate postemergence (POST) herbicides for hemp dogbane control in corn. Studies were initiated at no-tillage and chisel-plowed sites each of the three years. Nicosulfuron and primisulfuron were evaluated alone and in combination with 2,4-D amine or dicamba. In 1995 and 1996, CGA-152005 plus primisulfuron was also applied alone and in combination with 2,4-D or dicamba. Control varied among years and sites. Nicosulfuron, primisulfuron, and CGA-152005 plus primisulfuron applied alone controlled 30% of the hemp dogbane, and dicamba or 2,4-D alone controlled 42 and 66%, respectively. Tank mixtures of nicosulfuron, primisulfuron, or CGA-152005 plus primisulfuron with dicamba were more effective and more consistent than dicamba alone. Combinations of nicosulfuron, primisulfuron, or CGA-152005 plus primisulfuron with 2,4-D gave the most effective and consistent control across sites, with an average of 93% control. In general, treatments controlled only shoots that had emerged at the time of application. New shoots emerged following herbicide application at the chisel-tillage sites in 1994 and 1995 but not at the no-tillage sites. However, in 1996, shoot emergence following treatment occurred in both no-tillage and chisel-tillage sites.
Postemergence Chemical Control of Nodding Broomrape (Orobanche cernua) in Bidi Tobacco (Nicotiana tabacum) in India
Authors: Dhanapal Grama N. , Ter Borg Siny J. , Struik Paul C.
Published: March 2018

Broomrape is a severe problem in the continuous cropping of bidi tobacco in India. Fifteen herbicides were evaluated for postemergence control, at different dates and rates, in field experiments in Nipani, Karnataka State. The effects of the herbicides onOrobanchecontrol and growth and yield of tobacco were compared to the effects of handweeding and an untreated check. Following this screening experiment, four herbicides were selected for further testing. Glyphosate at 500 g ai/ha applied at 60 days after transplanting (DAT) and imazaquin at 10 g ai/ha applied at 30 DAT reduced the number of aboveground broomrape spikes by 75 to 80% and increased the tobacco yields by 80 to > 100% compared to the untreated plots. Imazethapyr and EPTC were found to be less effective for broomrape control, but they still led to substantially higher tobacco yield. None of the herbicide treatments resulted in yields higher than those in the hand-weeded plots. These plots probably did not yet reflect the potential yield of tobacco under broomrape-free conditions, due to nonemerged spikes. Toxicity to tobacco of all herbicides was higher for the higher rates tested. It was lowest with imazaquin.
Weed Management Strategies for No-Till Soybean (Glycine max) Grown on Clay Soils
Authors: Swanton Clarence J. , Vyn Tony J. , Chandler Kevin , Shrestha Anil
Published: March 2018

Weed management strategies are needed for no-till soybean grown on clay soils. The effect of several weed management strategies on weed biomass, soybean yield, and gross return were evaluated in 1993, 1994, and 1995 on clay soils at two locations in southern Ontario. Soybean seeds were planted in narrow (19 cm) and wide (76 cm) rows with or without a rye cover crop. Herbicide treatments included glyphosate alone, glyphosate followed by imazethapyr + metribuzin applied PRE, and glyphosate followed by acifluorfen + bentazon applied POST. Two additional treatments with interrow cultivation were included in the wide-row soybean plots with glyphosate and glyphosate + PRE treatments. A nontreated check plot without rye was also included. Presence of a cover crop did not affect weed biomass or soybean yield. The glyphosate + broadcast PRE treatment provided the most consistent weed control both in narrow- and wide-row soybean. The weed control in this treatment ranged from 92 to 100%. The other treatments provided variable weed control across years and locations. The narrow- row plots with glyphosate + broadcast PRE treatment provided the most consistent soybean yields that were generally higher than the other treatments and ranged from 2,560 to 3,420 kg/ha. Soybean yields varied across locations and years in other treatments. Similar weed control and soybean yields were obtained with banded PRE herbicide + interrow cultivation and PRE treatments; however, herbicide use was 60% lower in banded PRE herbicide + interrow cultivation treatment. Narrow-row soybean averaged 27% higher gross returns than wide-row soybean for all broadcast herbicide treatments. Narrow-row soybean with PRE herbicide provided the highest gross returns. No-till soybean in narrow rows with preplant glyphosate and broadcast PRE treatment was the most risk-efficient weed management system on clay soils.