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Search the abstracts from the WSSA Annual Meetings by entering values for one or more of the following items.
307 abstracts in the database
Displaying results 1 to 30 of 307
GIS enables users to visualize and analyze problems in a spatial environment. There are many aspects of invasive species that could benefit from the use of GIS and other spatial technologies. These include mapping and modeling invasive species, analyzing growth patterns, and using new web technologies to disseminate information about spatial attributes of invasive species. This introduction will serve as a primer for GIS and will introduce the technologies and methods available today that can aid in the management of invasive species.
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The recently developed Invasive Plant Atlas of the Mid-South, or IPAMS, is a web-based system designed to allow users to database invasive plant data and provides access to that data and other information for different invasive plant species. Other information that is provided includes distribution maps, identification helps, management techniques, and reporting information. Emphasis will be placed upon, but not limited to, invasive species populations within the Mid-South region. Data will be shared amongst other organizations as well as through the National Biological Information Infrastructure (NBII). The database will include numerous invasive plant species, although initial training workshops will focus on 40 invasive plant species. These 40 species represent six primary habitats. The primary habitats are aquatic, managed forests, pasture, right’s-of-way, row crop, and wildland. A training manual was developed for use at workshops across the Mid-South. The training manual includes an overview of the project and the invasive species problem, information on the identification characteristics of 40 plant species, the data form and data form variable definitions, and database user tools. The data form variables will include those established by the North American Weed Management Association (NAWMA) including general information, GPS location information, and invasive plant species information. The IPAMS system provides tools for users to manage their data within the database. A notification system is also provided to allow interested parties to be notified when certain species are located within certain areas. IPAMS provides up-to-date distribution maps through an ArcIMS system. IPAMS is to be a one-stop-boutique providing invasive locations, control/management/eradication methods, and reporting information so that individuals can effectively perform early detection and rapid response for invasive plant species threatening the desired landscape.
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Geographic Information Systems (GIS) are an invaluable tool in planning for management and in assessing the effectiveness of management techniques. GIS is a critical tool in developing a strategic lake management plan or in developing operational tactical plans for management applications. GIS can be used to rapidly estimate the amount of herbicides to be used in a given location by combining the treatment map with water depth information. GIS can also be used to flag sensitive areas, environmental hazards, water intakes, or other areas of concern. GIS systems are now routinely used during applications, to precisely meter in the amount of herbicides needed for a given site. Lastly, GIS is an important tool for assessment. Treatment areas can be sampled before and after treatment to provide estimates of effectiveness, identify problematic areas, and revise treatment strategies. Data collected can be analyzed using traditional statistical techniques, or using GIS tools.
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As the threat of non-native plant species increases, the development and refining of methods to detect and monitor these species to mitigate negative impacts is critical. The use of quantitative methods for aquatic plants has not become as standardized as other components in the aquatic systems, such as biotic or physical components. One cost effective and efficient method to survey large areas and collect large quantities of data on the abundance of aquatic macrophytes is to conduct a point intercept survey. The point intercept survey is a quantitative approach that collects presence/absence data rapidly with no samples to analyze and has an unequivocal end point, the plant species is either at a given location or not. The presence/absence method is generally the simplest approach, inexpensive, and has a low complexity. However, data sheets can become cumbersome especially during larger surveys and there is the possibility of data recorded wrong, not being recorded at all, or lost. Also, data entry errors are frequent and can pose serious problems with interpretations of collected data. For these reasons, we have refined point intercept surveys to include the use of computers enabled with GPS capability, coupled with software to collect and store site specific spatial data. The use of Farm Works Site Mate® mapping software was used to develop and construct database templates to collect and store spatially explicit data. The use of these technologies has increased survey efficiency, through decreasing survey time, data handling, and data entry errors.
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Waterhyacinth is an invasive aquatic species that chokes water bodies and affects ecological interactions. Chemical control has been the most commonly used tool for successful management of this plant. However, the evaluation of herbicide efficacy has always required ground-truth data to confirm if areas covered by waterhyacinth have been controlled after herbicide application. In order to measure spatial changes of waterhyacinth, two satellite images from Landsat 5 TM (900 m2 pixels) were acquired before and after herbicide application over Lake Columbus, MS in 2005. The herbicide used was dimethylamine salt of 2, 4-D applied by helicopter at a rate of 4.26 kg ae ha-1. An unsupervised classification of each satellite image was performed in ERDAS - Imagine software to separate vegetated areas from non-vegetated areas. The accuracy of each classified image was assessed using ground-truth data collected from point-intercept surveys facilitated by Global Positioning Systems (GPS). The evaluation of waterhyacinth coverage was performed pixel by pixel using a Boolean operator in ArcMap-ArcGIS software with Spatial Analyst. Sprayed areas (waterhyacinth coverage) were converted in pixels of 900 m2 and reclassified into 0 = non-sprayed and 1 = sprayed in order to evaluate them against non-vegetated areas = 0 and vegetated areas = 1 from the pre-herbicide application classified satellite image. The analysis of each output consisted in total pixel counts per class multiplied by 900 m2 and dividing it by 10,000 to get hectares cover. Total hectares of pre-herbicide application coverage (PreHAC) for the waterhyacinth coverage class were 36 hectares. A total reduction of 13 hectares was detected on post-herbicide application coverage (PostHAC). As a result, a 36% of waterhyacinth cover was diminished by a broadcast application of 2, 4-D. These results suggest that the use of Landsat imagery to evaluate the efficacy of large-scale herbicide applications and track aquatic plants spatial changes is feasible.
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Geographic Information Systems [GIS] are well suited for studies involving habitat delineation, habitat suitability indexing,and habitat spread. A GIS model can be constructed which identifies areas of convergence for the environmental and ecological factors which provide desirable habitat for a species of interest. GIS models can be refined using logistic regression models and other statistical permutations to get a more "real world" view of species dynamics. In this way it is possible examine where species occur and where they could spread. The case studies presented here use the ArcGIS suite of software with the ModelBuilder application to predict the presence of Eurasian watermilfoil (Myriophyllum spicatum) and model the spread of cogongrass (Imperata cylindrica).
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GIS enables a user to visualize spatial data in ways that are meaningful. GIS can be used to map invasive weed species and document how populations change over time due to the environment, or management practices that implemented. Data collected over time can be analyzed, and statistics developed that can describe the rate of change of a weed population, as well as the spatial stability of that population. This workshop will discuss some of these approaches, as well as demonstrate some of the techniques used to perform spatial-temporal analysis.
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Abstract An experiment was conducted in Karaj, Iran to study the response of annual blue grass(Poa annua) to some ACCase herbicides including: coldinafop_propagyl, diclofop_methyl and fenoxaprop-p-ethyl. The experiment was arranged as a factorial completely randomized design with 4 replications. The factors were: the type of herbicide (coldinafop_propagyl, diclofop_methyl and fenoxaprop-p-ethyl) and the growth stage of plant (In 2-3 leaf stage in green house, 2-3 leaf in cold room (4[[Unable to Display Character: Ċ]]) and 5-6 leaf stage in green house). Green house and cold room treatments were set to compare the difference between spraying in spring and fall because annual blue grass is a winter weed and germinate in fall. The result of this study shows that coldinafop propagil is a suitable post emergence herbicide for annual blue grass control in wheat and the best stage of growth for spraying is in 2-3 leaf stage in green house because the herbicide was not effective in cold room condition. Key Words: Poa annua, coldinafop propagyl, diclofop methyl, fenoxaparop-p-ethyl.
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Four field trials were conducted over a two-year period (2005, 2006) in Ontario to evaluate the tolerance of pinto and Small Red Mexican (SRM) beans to various preplant incorporated (PPI), preemergence (PRE), and postemergence (POST) herbicides. Trifluralin, dimethenamid-p, and S-metolachlor applied PPI caused minimal (< 8%) injury and had no adverse effect on plant height (H), shoot dry weight (SDW) and yield. Imazethapyr and flumetsulam applied PPI caused up to 13% injury and reduced H and SDW by up to 15 and 28%, respectively, but had no effect on yield. Pyroxasulfone PPI caused up to 80% injury and reduced H, SDW, and yield by 36, 63 and 38%, respectively. Dimethenamid-p and S-metolachlor applied PRE caused up to 19% injury, but had no effect on yield. Pyroxasulfone and linuron applied PRE caused as much as 33% visual injury and reduced H, SDW, and yield by up to 29, 36 and 25%, respectively. Imazethapyr, flumetsulam and cloransulam-methyl caused less than 5% injury and had no effect on H, SDW and yield. Bentazon POST applied once and twice at 840 g ai/ha and imazethapyr POST at 37.5 g/ha caused minimal injury (< 7%), but had no effect on H, SDW, and yield. Imazethapyr applied twice at 37.5 and in single and repeat applications containing 75 or 150 g/ha caused 15 to 44% injury but caused no adverse effect on yield except for imazethapyr applied twice at 150 g/ha which reduced yield 16%. The addition of bentazon to imazethapyr in a tankmix reduced injury by as much as 23%. Imazethapyr at 37.5 or 75 g/ha combined with bentazon at 840 g/ha applied once or twice caused 3 to 23% injury but had no adverse effect on H, SDW, and yield of dry beans except for two applications of imazethapyr at 150 g/ha plus bentazon at 840 g/ha which reduced H 16% and SDW 28%.
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Field experiments were conducted in 2003, 2006, and 2007 in Ontario to determine if reduced rates of imazathapyr tank-mixed with trifluralin applied pre-plant incorporated (PPI) can be used as an economically and environmentally feasible weed management strategy for broad spectrum weed control in white and kidney beans. There was minimal visible injury (< 5%) in white or kidney beans with the imazethapyr alone or in tank mix combination with trifluralin at all rates evaluated. The rate of imazethapyr required to provide a minimum of 80 and 95% control of green foxtail, common lambsquarters and common ragweed was reduced when tank-mixed with trifluralin (600 g ha-1). There was a trend to increased yield of white and kidney bean with increasing rates of imazethapyr applied alone and in combination with trifluralin. The low application rate of imazethapyr compared to trifluralin (75 vs. 600 g ai ha-1, respectively) resulted in an environmental impact (EI) of imazethapyr that was much less than trifluralin. Tank-mixes of imazethapyr with trifluralin will provide growers with a weed management strategy that causes only a minor increase in environmental impact, acceptable weed control and has potential to increase net returns.
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Studies were conducted in 2005, 2006, and 2007 to evaluate crop injury and compare yield where glyphosate or certain acetolactate synthase (ALS) inhibitor herbicides were applied postemergence broadcast to corn at either V4 or V7 growth stages. The postemergence herbicides compared in all three years were nicosulfuron at 35 g ai/ha, foramsulfuron at 37.1 g ai/ha, premix of nicosulfuron at 26.6 g ai/ha plus rimsulfuron at 13.3 g ai/ha, and glyphosate at 0.84 kg ae/ha. The premix of imazethapyr at 46.9 g ai/ha plus imazapyr at 15.4 g ai/ha was evaluated only in 2005. Rimsulfuron at 17.5 g ai/ha was evaluated in 2006 and 2007. The premix of nicosulfuron at 35 g ai/ha plus thifensulfuron 2.7 g ai/ha was evaluated in 2007. Adjuvants were included with the herbicides according to label directions. Corn plants in all treatments in the 2005 study had normal vegetative growth throughout the season. However, in 2006 and 2007 injury in the form of stunted plants and shortened internodes was observed when the premix of nicosulfuron plus rimsulfuron was applied to corn in the V7 growth stage. Similar injury was also observed when rimsulfuron, or the premix of nicosulfuron plus thifensulfuron were applied to V7 corn in 2007. Abnormal ears in the form of twisted rows or pinched areas were observed in all treatments, including the non-treated check. The amount of abnormal ears for the premix of nicosulfuron plus rimsulfuron applied to corn in the V7 growth stage was 40% in 2005, 20% in 2006, and 24% in 2007. These values exceeded those observed in non-treated checks in both studies. Other treatments that were applied at V7 and had a greater percent of abnormal ears than that of the non-treated check included rimsulfuron in 2006 and 2007, nicosulfuron in 2007, foramsulfuron in 2007, and the premix of nicosulfuron plus thifensulfuron in 2007. The only treatment applied at V4 that caused a significant percent of ears with abnormalities was the premix of nicosulfuron plus thifensulfuron in 2007. Glyphosate did not cause a significant amount of ear injury in any of the three studies. Delaying application until V7 growth stage caused corn grain yield to be less than that of the non-treated check for the premix of nicosulfuron plus rimsulfuron in 2006 and rimsulfuron in 2006. The yield of premix of nicosulfuron plus rimsulfuron was 13,151 kg/ha (based on ear weight) compared with 17,812 kg/ha for the non-treated check. Applying rimsulfuron alone at V7 resulted in 3,083 kg/ha less yield than that of the non-treated check in the 2006 study. The results of this research show that certain ALS inhibitor herbicides may injure corn, particularly when applied postemergence broadcast to plants that exceed the labeled growth stage. Only two herbicide treatments in one study limited corn grain yield when applications were delayed until V7.
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Crop injury from herbicide application or herbicide carryover is traditionally assessed by objective visual ratings. In many cases, it would be beneficial to find alternative and complimentary methods of assessing crop injury. Software is available for assessing percent ground cover from digital images. A handheld optical sensor using Greenseeker technology is able to quickly calculate the Normalized Difference Vegetative Index (NDVI), an indicator of plant health. There are also a number of hand-held meters available that measure light interception in a crop canopy and calculate the leaf-area index (LAI). To assess the ability of these tools to quantify injury to canola (Brasssica napus) and to predict canola yield or biomass production from residual herbicides, experiments were conducted at Scott, SK., Canada in 2006 and 2007. Varying rates of imazamox:imazethypyr (1:1), sulfosulfuron, and combinations of these two herbicides were applied to plots in the autumn previous to spring seeded Roundup Ready canola. Digital images, Greenseeker, and LAI measurements were taken 14, 21, and 28 days after seeding. In addition, visual injury ratings were taken at the same time. Biomass measurements (both fresh and dry weights) were taken at the time when canola was bolting. Seed yield was also collected. The digital images were analyzed with ASSESS software to determine percent groundcover. Results from the first year of the study indicated that data from digital image analysis, the LAI light meter, and the Greenseeker sensor correlated highly with visual injury ratings, as well as fresh and dry weight biomass and seed yield reduction. Second year data will also be presented. Of the three systems evaluated, the Greenseeker measurements can be done the quickest and requires limited knowledge and expertise.
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BAS 800H is a new herbicide being developed by BASF for broadleaf weed control in corn and other crops prior to crop emergence. Three field studies were conducted in Ontario, Canada over a two year period (2006 and 2007) to evaluate tolerance of spring cereals (barley, oats, and wheat) to preemergence and postemergence applications of BAS 800H at 50 and 100 g ai/ha. BAS 800H applied preemergence caused minimal visible injury (4% or less) at 3, 7, 14 and 28 days after emergence and had no adverse effect on height and yield of barley, oats, and wheat. BAS 800H plus Merge (1% v/v) applied postemergence caused as much as 80, 72, and 75% visible injury in barley, oats, and wheat, respectively. Injury decreased over time but was greater with the high rate. BAS 800H applied postemergence reduced plant height as much as 17, 13, and 21% and reduced yield as much as 29, 8, and 19% in barley, oats and wheat, respectively. Based on these results, BAS 800H applied preemergence at the proposed rate can be safely used in spring planted barley, oats and wheat; however, the postemergence application of BAS 800H results in unacceptable injury and yield loss. These results are consistent with the proposed preemergence burndown use pattern for BAS 800H.
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BAS 800H is a new herbicide being developed by BASF for preemergence (PRE) broadleaf weed control in corn. Field studies were conducted at two Ontario locations in 2006 and 2007 to evaluate tolerance of field corn to PRE and postemergence (POST; spike and 2-3 leaf stage) applications of BAS 800H at 50, 100 and 200 g ai/ha with and without an adjuvant. A wettable granule (WG) formulation of BAS 800H was used for the studies. BAS 800H at 100 g/ha applied PRE caused no visible injury in corn and there was no decrease in corn height or yield. BAS 800H at 100 g/ha applied POST at the spike stage caused up to 3% visible injury in corn but there was no decrease in corn height or yield. BAS 800H at 100 g/ha applied POST at the 2-3 leaf stage caused up to 6% visible injury and 4% decrease in height, but no decrease in yield. The addition of the adjuvant, Merge at 1% v/v resulted in up to 5 and 80% visible injury and a decrease in height of 9 and 59% when applied at the spike and 2-3 leaf stage, respectively. Generally, injury decreased over time but was greater with the high rate. These results confirm that BAS 800H applied PRE can be safely used in corn at rates up to 200 g/ha. While POST applications of BAS 800H plus Merge at the spike and 2-3 leaf stage result in unacceptable injury and yield loss in field corn, POST (spike and 2-3 leaf stage) applications at the rate of 50 or 100 g/ha without adjuvant demonstrated acceptable corn tolerance and may allow use beyond the proposed PRE use pattern.
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Camelina (Camelina sativa) together with other oilseed crops have garnered interest as potential sources of biodiesel. Experiments were conducted in 2006 and 2007 to determine herbicide tolerance of camelina. Two rates of eight preemergence (PRE) and ten postemergence (POST) herbicides were applied to camelina. PRE herbicides evaluated included: acetochlor, trifluralin, ethalfluralin, pendimethalin, triallate, metolachlor, sulfentrazone, and EPTC. POST herbicides evaluated included: fluroxypyr, bromoxynil, clopyralid, MCPA, 2,4-DB, bentazon, clethodim, sethoxydim, thifensulfuron, and tribenuron. PRE herbicides were applied prior to planting and POST herbicides were applied on 6 to 10 inch tall camelina plants. Camelina was seeded at 3 lb/A and treatments were replicated four times. The entire experiment was conducted weed-free in order to focus on herbicide tolerance. Treatments were compared to two nontreated controls. PRE herbicide injury typically was evident as stand reduction, while POST herbicide injury was recognizable as stunting/chlorosis. In both years at 6 weeks after preemergence treatment, stand reduction was less than 6% when trifluralin, ethalfluralin, pendimethalin, and triallate were applied at the full rate. Sulfentrazone completely eliminated camelina from treated plots regardless of rate. The other PRE herbicides reduced camelina stand 15 to 56% at the half rate and 17 to 70% at the full rate. In 2006, camelina seed yield, with the exception of sulfentrazone, did not differ from the nontreated controls regardless of rate. This result occurred because plants in plots treated with PRE herbicides that did survive became larger and produced more seed per plant compared to plants treated with herbicides that did not cause stand reduction. In 2007, camelina yield from plots treated with trifluralin, ethalfluralin, and pendimethalin were higher than yield from plots treated with acetochlor or triallate. In both years, stunting/chlorosis caused by applications of clopyralid, 2,4-DB, clethodim, and sethoxydim at 6 weeks after postemergence treatment was less than 6%. In both years, applications of either rate of thifensulfuron or tribenuron controlled camelina greater than 70%. Applications of MCPA controlled camelina from 56% with the half rate to 84% with the full rate. The other POST herbicides controlled camelina 8 to 40% at the low rates and 18 to 73% at the high rates. In both years, camelina in plots treated with clethodim, sethoxydim, and the low rate of bromoxynil produced yields equivalent to the nontreated controls. Plants in plots treated with clopyralid were essentially sterilized and did not produce seed. Results indicate that there are several herbicides that have the potential to be utilized in camelina for weed control, however additional research needs to be conducted to confirm these results.
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Research was conducted from 2003 to 2004 to determine herbicide tolerance levels for soft red winter wheat and glyphosate resistant and STS-glyphosate resistant soybean cultivars grown in rotation to the sulfonylurea herbicides mesosulfuron and sulfosulfuron. The soft red winter wheat cultivar 'AGS 2000' was planted in November 2003 and then mesosulfuron and sulfosulfuron were applied at 1X and 2X rates in December 2003. Wheat was evaluated for injury and harvested in May 2004. Four soybean cultivars ('Prichard RR', 'Asgrow 7601 RR', 'Dekalb 74480 RR', and 'Asgrow 4501 RR/STS') were evaluated for crop injury, stand, and yield. AGS 2000 wheat did not exhibit any injury symptoms nor yield differences as compared to the non-treated control (3840 kg/ha) from sulfosulfuron at the 1X (3860 kg/ha) and 2X (3770 kg/ha) or mesosulfuron at the 1X (3750 (kg/ha) or 2X (3790 kg/ha) rates. Soybean stand was not affected by either herbicide or rate. Mesosulfuron carryover was not a factor as there were no injury or yield differences for any soybean cultivar. Asgrow 4501 RR/STS and Dekalb 74480 were not affected by sulfosulfuron carryover. However, Prichard RR and Asgrow 7601 RR exhibited injury in the form of stunting and reduced growth due to sulfosulfuron carryover at the 1X (13 to 36%) and 2X (20 to 79%) rates. Sulfosulfuron carryover reduced yield of Asgrow 7601 RR when compared to the non-treated control (3350 kg/ha) by 50% for the 1X rate (2340 kg/ha) and 70% for the 2X rate (1680 kg/ha).
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Competitive crops or cultivars can be an important component of integrated weed management systems. A study was conducted from 2003 to 2006 at four sites across semiarid prairie ecoregions in western Canada to investigate the weed-suppression ability of canola (Brassica napus L.) and mustard (oriental mustard or canola-quality mustard, Brassica juncea L. Czern. & Coss; yellow mustard, Sinapis alba L.) cultivars. Four open-pollinated canola cultivars, four hybrid canola cultivars, two canola-quality mustard cultivars, two oriental mustard cultivars, and two yellow mustard cultivars were grown in competition with indigenous weed communities. Yellow mustard was best able to suppress weed growth, followed in decreasing order of weed competitiveness by oriental mustard, hybrid canola, open-pollinated canola, and canola-quality mustard. Weed-competitive ability of cultivars, assessed by total weed biomass, was correlated with time to crop emergence, early-season crop biomass accumulation (prior to bolting), and plant height.
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From 2003 to 2007, fall-applied herbicide combinations were evaluated to determine their impact on control of several weed species prior to planting soybean and/or corn the following spring in southeastern and central Pennsylvania. Depending on the location and year, herbicides were evaluated for control of common chickweed (Stellaria media), dandelion (Taraxacum officinale), purple deadnettle (Lamium purpureum), corn speedwell (Veronica arvensis), shepherd’s purse (Capsella bursa-pastoris), horseweed (Conyza canadensis), and downy brome (Bromus tectorum). Treatments were applied in late October to early November with a hand-held boom sprayer that delivered 187 L ha-1. 2,4-D was applied at 560 g ae ha-1; glyphosate at 860 g ae ha-1; chlorimuron plus tribenuron premix at 22.7 and 45.5 g ai ha-1; flumioxazin at 71.4 g; idosulfuron at 2.1 g; metribuzin at 526 g; rimsulfuron plus thifensulfuron premix at 26.2 g; and simazine at 1120 g. All treatments contained 2,4-D. Plots were replicated and randomized and measured 3 m wide by 9 m long. Ratings taken the following spring, prior to crop planting, revealed that treatments containing chlorimuron plus tribenuron always provided greater than 95% control of the broadleaf weeds present. Glyphosate plus 2,4-D provided greater than 90% control of downy brome, dandelion and shepherd’s purse and 80 to 89% control of the other species. Treatments containing flumioxazin provided 92 to 95% control of corn speedwell and shepherd’s purse but only 79 to 88% control of the other broadleaves. Idosulfuron-containing treatments controlled horseweed and common chickweed better (90 to 96%) than the other broadleaves (79 to 89%). Metribuzin was most effective on purple deadnettle and shepherd’s purse (>90% control) compared to 78 to 87% control for the other broadleaf weeds. Treatments containing rimsulfuron plus thifensulfuron or simazine provided >90% control of horseweed, common chickweed, purple deadnettle, and shepherd’s purse and about 85% control of dandelion. Simazine provided 92% speedwell control. Fall herbicide applications can provide effective control of many winter annual and simple perennial weeds. Although several other herbicides are labeled for fall application, the above herbicides provide the foundation for most fall burndown programs.
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Volunteer corn is an emerging weed control issue in soybeans with the continued adoption of glyphosate-resistant corn hybrids. The objective of this research was to evaluate various herbicides for control of volunteer glyphosate-resistant corn in glyphosate-resistant soybeans. Two field studies were conducted in Indiana. One location was in northwestern Indiana and the other was in southeastern Indiana. Both trials were treated the same. Glyphosate resistant seed corn was spread on the trial and shallowly incorporated with a field cultivator. Glyphosate-resistant soybeans were planted in 76 cm rows. Various post application herbicides were applied when corn was 25- to 38- cm or 56- to 66- cm tall. At the 25- to 38- cm timing, clethodim provided 97 to 100 percent control and quizalofop provided 91 to 100 percent control. At the 56- to 66- cm timing, imazethapyr, quizalofop and clethodim provided 88 to 98 percent control.
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Site-specific weed management can encompass both limiting treatment to areas of the field where weed pressure is above the economic threshold (patch spraying) and varying the choice of herbicide for most cost-effective weed control of local populations. The potential benefits of patch spraying with multiple, postemergence treatments in irrigated corn was evaluated in simulation studies using weed counts from 16 fields. Patch spraying with one, two or the number of treatments that maximized net return for a field was simulated. With patch spraying with one treatment, the average area of a field left untreated was 34.5% and net return increased $3.09/ha and crop yield decreased by.05% of weed-free yield compared to the uniform application. Patch spraying with two or more treatments in a field increased net return by more than $4.94/ ha with just a small increase (4%) in the area of the field treated. Net return increases with patch spraying with one treatment because herbicide cost is reduced. With additional treatments, net return increased in a field because herbicide cost was reduced, crop yield was increased or both. Grasses were controlled better with multiple rather than a single treatment for patch spraying and the variability of escapes within a field was changed. Up to eight treatments were recommended for patch spraying with multiple treatments, but there may be little benefit in using more than three treatments within a field. Moreover, herbicide use may be substantially increased. Benefits varied among fields with a net return of $8.23/ha or more in half of the fields and a maximum of $19.20/ha with two treatments. Patch spraying may be best recommended as a strategy of using multiple treatments within a field in addition to leaving some areas untreated in a field and as a strategy that is appropriate in some fields rather than a standard replacement for uniform application.
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Prickly lettuce has become a widespread and troublesome weed in the Pacific Northwest. It occurs in all rainfall zones and is difficult to control largely due to ALS resistance but also due to increased tolerance to 2,4-D and glyphosate. Although prickly lettuce is not a relatively competitive weed in-crop, it can deplete the soil of moisture for following crops. In wheat fields adjacent to Pullman, WA, several individual plants within a prickly lettuce population were observed to survive two separate broadcast applications of a glyphosate plus 2,4-D in mixture (0.84 kg ae/ha each). Other broadleaf weed species and most prickly lettuce plants within the treated area were effectively controlled. Consequently, seed were collected from the surviving plants to determine tolerance to glyphosate and 2,4-D. The objectives of this study where to identify any antagonistic interactions of 2,4-D and glyphosate for control of prickly lettuce and to determine response of putatively resistant prickly lettuce biotypes to increasing rates of 2,4-D. When glyphosate and 2,4-D where applied in mixture at 0.42 kg ae/ha, antagonism was observed in prickly lettuce found to be resistant to 2,4-D. Conversely, synergism was observed when the same treatment was applied to susceptible prickly lettuce. In dose response experiments, the resistant prickly lettuce biotype was found to be 27-fold more resistant to 2,4-D than the susceptible biotype. The resistant prickly lettuce biotype is cross-resistant to MCPA and dicamba, but not to aminopyralid or fluroxypr.
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Herbicide-tolerant crops increase weed management options in these systems. Tolerance to glufosinate-ammonium has been bioengineered into cotton (Gossypium hirsutum L.) by Agrobacterium tumefaciens through the expression of a gene encoding the enzyme phosphinothricin acetyl transferase. Laboratory studies conducted to determine thermal limitations on herbicide activity in bioengineered cotton concluded that glufosinate-tolerant cotton should not be damaged over a wide range of application temperatures. Additional field and growth chamber studies have confirmed that transgenic glufosinate-tolerant cotton has high levels of glufosinate tolerance (up to 8X labeled rates). Glufosinate-tolerant (LibertyLink) cotton was commercially available in the United States in 2004 and Australia in 2006, with commercial availability in Brazil expected in 2008. In 2006, LibertyLink cotton was planted on 3.5% of U.S. cotton hectares. Texas planted 7.7% of its cotton hectares to this technology, and planted hectares in other states are expected to increase as adapted varieties become available across the cotton belt. To achieve effective weed control with glufosinate, weed size and spray coverage are critical for maximum herbicidal activity. The glufosinate-ammonium label recommends a maximum weed height of 8 cm for Palmer amaranth (Amaranthus palmeri) and 5 cm for devil’s-claw (Proboscidea louisianica) when applying the 0.47 kg ai/ha rate. To accomplish season-long weed control, sequential glufosinate applications were necessary throughout the growing season. The objective of this research was to evaluate Palmer amaranth and devil’s-claw control following glufosinate applications at different rates, timings, and in sequential combinations when weed size exceeded label recommendations. Glufosinate at 0.87 kg ai/ha controlled Palmer amaranth 75% following the early-postemergence (EP) application. This control was more effective than glufosinate at rates of 0.58 (53%) and 0.45 kg ai/ha (29%). Palmer amaranth was controlled 47% (0.45 fb 0.45 kg ai/ha) to 90% (0.58 fb 0.87 kg ai/ha) following EP fb mid-postemergence (MP) sequential applications. Glufosinate applied late-postemergence (LP) did not effectively control Palmer amaranth (<60%) regardless of rate. Three applications of glufosinate (EP fb MP fb LP) controlled Palmer amaranth 73 to 86%. More effective Palmer amaranth control was observed when the EP application contained glufosinate at 0.87 kg ai/ha compared to glufosinate at 0.45 kg ai/ha. Glufosinate at 0.45 kg ai/ha applied EP controlled devil’s-claw 90%. If the glufosinate rate increased to 0.58 or 0.87 kg ai/ha, devil’s-claw control increased (96%). Two glufosinate applications (EP fb MP) controlled devil’s-claw at least 99% regardless of rate. Devil’s-claw control ranged from 20 to 58% with a single LP application. Devil’s-claw control following sequential glufosinate applications (EP fb MP fb LP) did not improve from the addition of prometryn PRE in 2006. These data indicate the importance of weed size at application.
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Failure of glyphosate to control Palmer amaranth was first reported in Arkansas in Mississippi County in June 2005. The objectives of this research were to a) confirm glyphosate-resistant Palmer amaranth in Arkansas, b) quantify the level of glyphosate resistance compared to known susceptible accessions that had not been previously exposed to glyphosate and c) determine the effectiveness of postemergence-applied herbicides with different modes of action in controlling the glyphosate-resistant biotype compared to glyphosate-susceptible accessions. The LD50 values were similar among three susceptible Palmer amaranth accessions, ranging from a low of 24.4 to a high of 35.5 g ae/ha glyphosate. The resistant biotype had an LD50 of 2819 g/ha glyphosate, which was 79- to 115-fold greater than the susceptible biotypes and 3.4 times a normal glyphosate use rate of 840 g/ha. In addition to glyphosate, fifteen herbicides encompassing eight modes of action were evaluated for postemergence control of the glyphosate-resistant Palmer amaranth biotype. The glyphosate-resistant biotype was effectively controlled with most of the evaluated herbicides, but the use of acetolactate synthase-inhibiting herbicides such as pyrithiobac, trifloxysulfuron, and imazethapyr is not a viable option for Palmer amaranth control.
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Previous research suggests that early-season detection of light quality signals among neighboring plants may be an important mechanism affecting crop-weed interactions. Increased reflection of far-red light among increased plant densities can lower the red:far-red ratio (R:FR) of horizontally propagated light before shading occurs among plants. Limited evidence suggests that altered light quality can influence early growth and development of corn, but it is not understood how responses to early-season low R:FR (associated with higher total plant densities in corn-weed communities than in weed-free corn) affect season-long growth and productivity of corn. Field experiments were conducted in 2005 and 2006 to determine the effect of low R:FR on early-season corn growth and morphology, and late-season corn plant biomass and grain yield. Corn was planted at 53,800 and 107,600 plants ha-1 to establish control and low early-season R:FR environments, respectively. The control density treatment represented a typical weed-free corn environment, whereas the high density treatment simulated a competitive corn-weed community. The high density treatment was thinned to the control plant density at the time of mutual shading (V6-7 corn) and simulated weed removal. Light quality (R:FR, 645:735 nm) was measured twice weekly from VE corn to the time of mutual shading. Photosynthetically active radiation was measured daily to determine the time of mutual shading. The R:FR was nearly 50% less at the time of mutual shading in the high density corn treatment (0.24) than the control density treatment (0.43). Measurements of soil moisture availability, soil nutrient availability, and corn leaf tissue nutrient status indicated that soil moisture and nutrient availability were not limiting and did not differ among light quality environments. In 2005, early-season low R:FR had little effect on corn plant morphology at the time of mutual shading. In contrast, low R:FR was associated with taller plants, longer leaves, and less tiller mass than corn plants in the control R:FR in 2006. The root:shoot ratio did not differ between light quality environments at the time of mutual shading in either year. At physiological maturity, above-ground plant biomass and corn grain yield did not differ between early-season light quality environments. These results indicate that early-season light quality effects on corn morphology were transitory and did not affect corn yield, and suggest that early-season low R:FR typically associated with corn-weed communities was not a key determinant of corn yield in the field environment when water and nutrients were not limiting factors.
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Field trials were conducted to evaluate phytotoxicity and weed control efficacy when crop oil concentrate and methylated seed oil adjuvants were tank mixed with tembotrione and isoxadifen. Reduced rates of tembotrione and isoxadifen were used to separate differences between adjuvants. Phytotoxicity was very low, regardless of adjuvant type. Therefore, adjuvant selection should not be limited by phytotoxicity concerns. Generally, weeds that are very sensitive to tembotrione and isoxadfen are controlled at high levels regardless of adjuvant type. Velvetleaf (Abutilon theophrasti) control was 93% and 94% when crop oil concentrate and mehtylated seed oil were tank mixed with tembotrione and isoxadifen. However, weeds that are less sensitive to tembotione and isoxadifen do respond to adjuvant type. Methylated seed oils provide increase control for those weeds which are difficult to control. Adding low rates of atrazine to tembotrione and isoxadifen increases weed control. Giant foxtail (Setaria faberia) control increased from 78% to 93% when atrazine was added to tembotrione and isoxadifen and when crop oil concentrate was the adjuvant. Adjuvant selection becomes less critical when atrazine is tank mixed. Fall panicum (Panicum dichotomiflorum) could not be controlled regardless of adjuvant type or addition of atrazine.
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A field study was conducted in 2007 to characterize the response of a giant ragweed population from Pickaway County, Ohio to preemergence and postemergence applications of ALS inhibitors and glyphosate. The response of individual plants and overall control were measured 21 DAT and in October at the end of the growing season. ALS inhibitors applied postemergence (chlorimuron-ethyl, cloransulam-methyl, and imazamox) controlled less than 43% of the giant ragweed 21 DAT, and control with glyphosate did not exceed 59%. A mixture of cloransulam plus glyphosate did not improve control, compared with application of either alone. At least 78% of the individual plants marked prior to application survived treatment with ALS inhibitors, glyphosate, or a mixture of cloransulam and glyphosate at 21 DAT. These studies confirm the presence in Ohio of a giant ragweed biotype with multiple herbicide resistance, to glyphosate and ALS inhibitors.
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Annual grass control is a limiting factor to production of pearl millet (Pennisetum glaucum). Previous studies indicate that pearl millet displayed is tolerant to mesotrione applied PRE, but limited tolerance was observed from POST applications of mesotrione. Field and greenhouse studies were conducted to evaluate the response of pearl millet to three HPPD inhibiting herbicides when applied PRE and POST. In the greenhouse, most pearl millet varieties exhibited good tolerance to mesotrione applied PRE. In a greenhouse comparison of 20 pearl millet varieties, the ED10 ranged from 15 (Tif 23DB) to 198 g ai/ha (Tif 306) and the ED50 values ranged from 52(Ti f 23DB) to 309 g /ha (Tif 306). For mesotrione applied POST (applied at 3-4 leaf stage of pearl millet with 0.25% v/v NIS), the ED10 for Tif102 was 92 g/ha while the ED50 was 140 g/ha. When the safener, isoxadifen, was added at a 1:1 ratio to mesotrionen to POST applications of mesotrione, the ED10 was reduced by 49% to 62 g/ha and the ED50 was reduced by 52% to 67 g/ha. In the field, the ED10 of mesotrione applied PRE to Tif102 was 102 g/ha while the ED50 was 310 g/ha. Pearl millet (Tif 102) treated with mesotrione applied POST (3-4 leaf stage with 0.25% v/v NIS) had injury ratings ranging from 32% 7 DAT at 100 g/ha to 72% at 500 g/ha. When isoxadifen was tank-mixed in a 1:1 ratio with mesotrione applied POST, injury from a 100 g/ha mesotrione treatment was reduced to 8%. At 21 DAT, pearl millet injury declined to 7% at 100 g/ha with or without the addition of isoxadifen. Other HPPD-inhibiting herbicides tembotrione and topremazone were evaluated for pearl millet tolerance. Topremazone applied POST at 18 g ai/ha caused 70% injury 7 DAT and this declined to 35% by 21 DAT. The addition of isoxadifen at a 1:1 ratio to topremazone reduced injury from topremazone applied at 18 g/ha to 43% 7 DAT and this declined to 18% 21 DAT. In greenhouse studies, tembotrione applied POST in a 2:1 ratio with isoxadifen resulted in an ED10 of 42 g ai/ha at 7 DAT and an ED50 of 49 g/ha. These studies indicate that pearl millet has good tolerance to mesotrione applied PRE and when mixed with isoxadifen, good tolerance when applied POST. Pearl millet is not as tolerant to topremazone and tembotrione applied POST as mesotrione.
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Glyphosate has revolutionized weed control in cotton (Gossypium hirsutum). Repetitive use of glyphosate and in most cases sole reliance on glyphosate has led to development of glyphosate-resistant weeds. Glyphosate-resistant horseweed (Conyza canadensis), Palmer amaranth (Amaranthus palmeri), and Italian ryegrass (Lolium multiflorium) have been documented in cotton in states across the southern US cotton region. The advent of glyphosate resistance and shifts to weed species that proliferate in a total glyphosate weed control program, such as late-season annual grasses, necessitate inclusion of residual herbicides in a glyphosate-based weed control program. KIH-485 is a new chemistry under investigation for its potential to supplement glyphosate-based weed control programs in the southern US cotton. Experiments were conducted on or near the Delta Research and Extension Center, Stoneville, MS. Soil type was a Dundee silt loam. Experiments were conducted to evaluate KIH-485 in burndown, preemergence (PRE), or postemergence (POST) programs. Treatments were applied in early March (Burndown), early May (PRE), or to 1-leaf (EPOST), 4-leaf (MPOST), or 6-leaf (LPOST) cotton in the POST trial. KIH-485 was applied at rates ranging from 0.044 to 0.186 lb ai/A. KIH-485 was applied with glyphosate (0.77 lb ae/A) plus dicamba (0.25 lb ae/A) in all burndown treatments. KIH-485 was applied alone in PRE treatments and with glyphosate (0.77 lb ae/A) in all POST treatments. Roundup Ready Flex cotton was planted in late April (burndown trial) to early May (PRE and POST trials). A nonionic surfactant at 0.25% v/v was added to all POST treatments. Treatments were applied with a CO2-propelled backpack sprayer equipped with 11003 flat fan nozzles at a delivery rate of 15 gallons per acre. Weed control and cotton injury was documented throughout the growing season. Weeds evaluated included browntop millet (Brachiaria ramosa) in the burndown trial, Palmer amaranth (PRE and POST trials), and barnyardgrass (Echinochloa crus-galli) in the burndown, PRE, and POST trials. Data were subjected to the SAS PROC MIXED procedure. Least square means were calculated and mean separation for treatments were produced at P≤0.05. Burndown and PRE applications of KIH-485 resulted in no cotton injury. Cotton injury from POST applications of KIH-485 was transient as injury ranged from 13 to 18% by two weeks after treatment when applied to 4-leaf cotton as compared to 0% injury by four weeks after treatment. KIH-485 applied to 1-leaf or 6-leaf cotton resulted in no cotton injury. Browntop millet and barnyardgrass control was as high as 99% by 12 weeks after treatment with burndown and PRE applications of KIH-485. Palmer amaranth and barnyardgrass were controlled 90 to 100% by 4 weeks after treatment with PRE or POST applications of KIH-485. Residual control of small seeded broadleaves and grasses can be excellent with KIH-485. This new chemistry, once registered, can be an excellent residual tool for managing weeds in a glyphosate-based weed control programs and potentially prevent the advent of glyphosate-resistant weeds.
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The loss of methyl bromide for use as a preplant soil fumigant is inevitable. Research was conducted to evaluate the most promising alternatives in large-plot on-farm trials. Methyl bromide plus chloropicrin (MB) 57:43 at 400 lb/A (448 kg/ha) under low density polyethylene (LDPE) mulch was compared to three alternatives including 1) methyl idodide plus chloropicrin (MIDAS) 50:50 at 175 lb/A (196 kg/ha) under virtually impermeable film, 2) dimethyl disulfide plus chloropicrin (DMDS) 79:21 at 75 gal/A (700 l/ha) under LDPE mulch, and the 3-WAY (1,3-D [Telone II at 12 gal/A (112 l/ha)] followed by chloropicrin [150 lb/A (168 kg/ha)] followed by metam sodium [Vapam 75 gal/A (700 l/ha)]) under LDPE mulch. Rates provided are broadcast but treatments applied as in-bed banded application. The experiment was conducted on three Georgia vegetable farms with plot sizes ranging from 0.12 to 0.4 A. Treatments were replicated four times. Bell pepper was planted and pepper heights, stand, and weed emergence were measured throughout the season. Two to four harvests occurred with the entire plot being picked by each grower’s harvesting crew. After each harvest, fruit was processed through the packing house and fruit graded identical to the grower’s standard process. The number of boxes for each fruit grade for each plot was counted. Pink purslane and morningglory species were controlled similarly by fumigants. Nutsedge and amaranth were controlled less effectively by DMDS than by other fumigants. Fumigants did not impact pepper growth or plant stand. Pepper yields ranged from 1300 to 2000 boxes per acre depending on location. No differences in the number of culls or suntan fruit were noted. The number of pepper boxes produced with MIDAS was similar to MB with the one exception of less choice fruit produced for cumulative harvests at one location. At this same location, the MIDAS system produced 12% more jumbo fruit than MB; while this difference was not significant, it may have led to the production of less choice fruit. The total number of jumbo, extra large, large and choice fruit produced by MIDAS was 97% of that produced by MB. DMDS produced less jumbo, choice, and extra large fruit each at one location when compared to MB. The total number of jumbo, extra large, large and choice fruit produced by DMDS was 92% of that produced by MB. At two locations, the 3-WAY produced more jumbo fruit but less extra large and large fruit when compared to MB. The total number of jumbo, extra large, large and choice fruit produced by 3-WAY was 97% of that produced by MB. Economic returns are being generated and will be reported at the WSSA.
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The use of flame weeding is becoming more common as organic production continues to increase in popularity. The current study is part of a project designed to evaluate the use of flame weeding for post-emergent weed control in horticultural crops. Flame treatments were applied in experiments of Spanish onion, broccoli, spinach, and beets in 2005 and 2006. Fifteen flaming doses, controlled by driving speed and fuel pressure, were tested, ranging from 5.63 to 32.78 kg ha-1. Experimental plots received a single flame treatment at one of five time points during the growing season. Dose-response curves were then constructed according to weed species and growth stage. In 2006, in order to guarantee sufficient numbers to ensure accurate data, fields were seeded with and assessments limited to common lambsquarters (Chenopodium album L.), redroot pigweed (Amaranthus retroflexus L.), barnyardgrass (Echinocloa crus-galli L. Beauv.), and yellow foxtail (Setaria glauca L. Beauv.). Lambsquarters was able to be effectively controlled up until the 6 leaf stage, although higher doses were required for more advanced plants. In 2006 better than 95% control of lambsquarters at the cotyledon stage was achieved at 7.5 kg ha-1, whereas the six leaf stage required a dose of 21.85 kg ha-1. The response of redroot pigweed was similar to that of lambsquarters in 2006. At the one leaf stage, the LD50 of redroot pigweed was 6.82 kg ha-1, and by the three leaf stage had increased to 9.04 kg ha-1. Approximately 95% control was attained in maturity stages up until the four leaf stage; higher doses were required for more mature plants. Complete control was not achieved even at the highest doses in the six leaf stage. Flame treatments were not able to effectively control grass weeds in this study. Even at the highest rate tested, approximately 33 kg ha-1, greater than 80% of weeds survived flame treatment at all maturity stages evaluated. These results suggest that flame weeding can be used to effectively control some, but not all, annual weed species. Compared to other species, dicots with upright growth forms and unprotected meristems appear to be more effectively controlled using flame weeding. Overall these data agree with previous reports in the literature regarding weed response to flame cultivation.
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