Browsing by Author "Askew, Shawn D."

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    2021 Home Grounds and Animals PMG - Author Contact List
    Askew, Shawn D.; Wycoff, Stephanie B.; Bergh, J. Christopher; Bush, Elizabeth A.; Day, Eric R.; Del-Pozo, Alejandro; Derr, Jeffrey F.; Frank, Daniel L.; Hansen, Mary Ann; Hong, Chuan X.; Laub, Curtis A.; McCall, David S.; Miller, Dini M.; Nita, Mizuho; Parkhurst, James A.; Paulson, Sally L.; Pfeiffer, Douglas G.; Rideout, Steven L.; Wilson, James; Yoder, Keith S. (Virginia Cooperative Extension, 2021-02-12)
    This is a chapter of the 2021 Home Grounds and Animals PMG. This 2021 Virginia Pest Management Guide provides the latest recommendations for controlling diseases, insects, and weeds for home grounds and animals. This publication contains information about prevention and nonchemical control as alternatives to chemical control or as part of an integrated pest management approach. The chemical controls in this guide are based on the latest pesticide label information at the time of writing. Because pesticide labels change, read the label directions carefully before buying and using any pesticide. Regardless of the information provided here, always follow the latest product label instructions when using any pesticide. Commercial products are named in this publication for informational purposes only. Virginia Cooperative Extension does not endorse these products and does not intend discrimination against other products that also may be suitable.
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    2021 Home Grounds PMG - Index
    Askew, Shawn D.; Wycoff, Stephanie B.; Bush, Elizabeth A.; Day, Eric R.; Del-Pozo, Alejandro; Derr, Jeffrey F.; Frank, Daniel L.; Hansen, Mary Ann; Laub, Curtis A.; McCall, David S.; Miller, Dini M.; Nita, Mizuho; Parkhurst, James A.; Paulson, Sally L.; Pfeiffer, Douglas G.; Rideout, Steven L.; Wilson, James; Yoder, Keith S.; Hong, Chuan X. (Virginia Cooperative Extension, 2021-02-12)
    This is a chapter of the 2021 Home Grounds and Animals PMG. This 2021 Virginia Pest Management Guide provides the latest recommendations for controlling diseases, insects, and weeds for home grounds and animals. This publication contains information about prevention and nonchemical control as alternatives to chemical control or as part of an integrated pest management approach. The chemical controls in this guide are based on the latest pesticide label information at the time of writing. Because pesticide labels change, read the label directions carefully before buying and using any pesticide. Regardless of the information provided here, always follow the latest product label instructions when using any pesticide. Commercial products are named in this publication for informational purposes only. Virginia Cooperative Extension does not endorse these products and does not intend discrimination against other products that also may be suitable.
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    2021 Horticultural and Forest PMG - Authors
    Askew, Shawn D.; Baudoin, Antonius B.; Bergh, J. Christopher; Chamberlin, Lori; Dary, Eric R.; Del-Pozo, Alejandro; Derr, Jeffrey F.; Frank, Daniel; Hansen, Mary Ann; Hong, Chuan X.; Johnson, Charles S.; Laub, Curtis A.; McCall, David S.; Nita, Mizuho; Parson, Rachel; Peer, Kyle; Pfeiffer, Douglas G.; Richardson, Robert J.; Salom, Scott M.; Schultz, Peter B.; Wilson, James (Virginia Cooperative Extension, 2021-02-12)
    Horticultural and Forest Crops 2021 Author Contact List
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    2021 Horticultural and Forest PMG - Low Management Crops and Areas
    Richardson, Robert J.; Askew, Shawn D. (Virginia Cooperative Extension, 2021-02-12)
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    2021 Horticulture and Forest PMG - Turf
    McCall, David S.; Del-Pozo, Alejandro; Laub, Curtis A.; Askew, Shawn D. (Virginia Cooperative Extension, 2021-02-12)
    This is a chapter from the 2021 Horticulture and Forest Pest Management Guide. The Virginia Pest Management Guide (PMG) series lists options for management of major pests: diseases, insects, nematodes, and weeds. These guides are produced by Virginia Cooperative Extension and each guide is revised annually. PMG recommendations are based on research conducted by the Research and Extension Division of Virginia Tech, in cooperation with other land-grant universities, the USDA, and the pest management industry.
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    Assessing Drift and Lateral Mobility of Flazasulfuron and Trifloxysulfuron Sodium
    Jester, Jennifer Lynn (Virginia Tech, 2009-12-04)
    Flazasulfuron is one of the newest sulfonylurea (SU) herbicides to be registered for use in the fine turf industry. Flazasulfuron is safe for use on bermudagrass (Cynodon dactylon), and zoysiagrass (Zoysia japonica) yet controls several grass, broadleaf, and sedge weeds. In fine turf, flazasulfuron controls cool-season grasses such as tall fescue (Festuca arundinacea) and perennial ryegrass (Lolium perenne) without harming warm-season grasses. Although SU herbicides like flazasulfuron bring several potential benefits to turfgrass markets, there are also several concerns related to using these herbicides in turfgrass areas. For many plant species, SU herbicides can cause phytotoxicity or death at less than 1 g ai/ha-1indicating small quantities of active ingredient are required to cause problems if herbicide moves in the environment. Herbicide moves to nontarget plants either after it has been applied via lateral relocation or during application via spray drift. Trials were conducted to evaluate flazasulfuron and trifloxysulfuron sodium tracking, runoff and drift in turfgrass environments. Field trials were conducted at six locations across the US to evaluate effects of irrigation, herbicide treatment, nontreated buffer distance, and time of tracking on creeping bentgrass (Agrostis stolonifera) putting green response to dislodged herbicide residues. Although average turf injury did not exceed 2%, significant differences were noted when treated plots were irrigated prior to tracking. In addition, putting green injury was negatively correlated and normalized difference vegetative index was positively correlated with increasing buffer distance. Data indicate the importance of post treatment irrigation to reduce lateral relocation of SU herbicides like flazasulfuron and trifloxysulfuron sodium in turfgrass. In other studies, herbicides were applied to turfgrass on 7 to 11 % slopes and perennial ryegrass injury was assessed at various distances down slope following an irrigation or rainfall event. Herbicide movement in runoff water was indicated by perennial ryegrass discoloration as much as 18 m below treated plots when excessive herbicide rates were applied to saturated soils. Based on perennial ryegrass injury, flazasulfuron at the rates tested was equivalent or more mobile than trifloxysulfuron sodium and equivalent or less mobile than pronamide when subjected to irrigation or rainfall soon after application to saturated soils. To assess spray drift, a bioassay based on corn height reduction was conducted and corn plants were exposed to potential spray drift in field conditions using conventional turfgrass spray equipment. A sprayer was operated when wind speeds were between 6.4 and 9.6 km h-1 and sentry plants were placed various distances between 0 and 30 m down wind. Wind speeds and direction were confirmed with anemometers and neutrally-buoyant balloons. Herbicide drift was not detected beyond 4.6 m downwind of either herbicide application. Data suggest a 5- to 8-m nontreated buffer area should sufficiently protect neighboring cool-season turfgrasses and other plants against flazasulfuron drift, runoff, and tracking as long as product is not applied to saturated soils and irrigated prior to traffic.
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    Assessing Spray Deposition and Weed Control Efficacy from Aerial and Ground Equipment in Managed Turfgrass Systems
    Koo, Daewon (Virginia Tech, 2024-05-24)
    There is a growing interest in agricultural spray drone (ASD) use for herbicide application in managed turfgrass systems, which historically has precluded aerial application. Considering pesticide deposition accuracy is of utmost importance in managed turfgrass systems, a thorough examination of factors that influence ASD spray deposition patterns is needed. A python-based spray deposition pattern analysis tool, SprayDAT, was developed to estimate spray quality utilizing a cost-effective continuous sampling technique involving digital soand spectrophotometric analysis of blue colorant stains on white Kraft paper. This technique cost 0.2 cents per USD spent on traditional water-sensitive paper (WSP) allowing for continuous sampling necessary for the highly variable deposition patterns delivered by an ASD. SprayDAT conserved droplet densities and more accurately detected stain objects compared to a commonly utilized software, DepositScan, which overestimated stain sizes. However, droplet density exhibited an upper asymptote at 22% stain cover when relating volume median diameter (VMD) due to increasing overlap of stain objects. Spread factor of blue colorant stains was fit to a 2-parameter power equation when compared across six discrete droplet sizes between 112 and 315 µm when droplets were captured in a biphasic solution of polydimethylsiloxane of 100 cSt over 12,500 cSt viscosities. Cumulative digitally assessed stain objects underestimated application volume 270% when compared to the predicted output based on flow rate, coverage, and speed. SprayDAT incorporates a standard curve based on colorant extraction and spectrophotometric analysis to correct this error such that total stain area accurately estimates application volume to within 9%. This relationship between extracted colorant and total stain area, however, is dependent on droplet size spectra. SprayDAT allows users to customize standard curves to address this issue. Using these analysis techniques, continuous sampling of a 29.3-m transect perpendicular to an ASD or ground sprayer spray swath resolved that increasing ASD operational height increases drift and effective swath width while effective application rate, total deposition, and smooth crabgrass control by quinclorac herbicide decreases. Deposition under the ASD was heterogeneous as the coefficient of variation (CV) within the targeted swath exceeded 30% regardless of operational height. At higher operational heights, relative uniformity of spray pattern was improved but droplet density at 11.7 m away from the intended swath edge was up to four times greater and total spray deposited was up to 60% reduced at the highest heights. For each 1-m increase in ASD operational height, 6% of the deposited spray solution, 11% of the effective application rate within the targeted swath, and 7% of smooth crabgrass [Digitaria ischaemum (Schreb.) Schreb. ex Muhl.] population reduction declined. Subsequent studies suggested that total deposition loss with increasing operational height of ASD were likely due to droplet evaporation. Discrete-sized droplets subjected to a 5-m fall in a windless environment exhibited a sigmoidal relationship where 98% volume of 135-µm droplets and approximately 67% volume of 177 – 283 µm diameter droplets evaporated. Addition of drift reduction agents (DRAs) or choosing different nozzle types altered the initial droplet density generated by a flat-fan nozzle. Regardless of DRA additions or nozzle replacement, the distance required to lose 50% of small droplets (< 150 µm diameter) was 6.6 m. Air induction nozzles and DRA admixtures also conserved smooth crabgrass control across 2- and 6-m operational heights, where control was reduced at the 6-m height with a flat fan nozzle without DRA. Spray deposition pattern analysis for multipass ASD and ground applications was conducted by utilizing nighttime UV-fluorescence aerial photography and weed infestation counts in a digitally overlaid grid. Results show that under-application across all devices was consistent and averaged 12%, whereas at least 14% more over-application on the targeted area was observed for ASD, regardless of equipped nozzle types, compared to a ride-on sprayer. Drift also occurred at least 3 times more for ASD application than for a ride-on sprayer and a spray gun sprayer. Using smooth crabgrass infestation annotated from aerial images could not consistently resolve the spatial variability evident in UV-fluorescent imagery presumably due to the innate variability in weed populations. Analysis using SprayDAT revealed insights into factors affecting ASD spray deposition, such as operational height impacting drift, effective swath width, and herbicide efficacy, highlighting the tool's utility in optimizing aerial herbicide applications in turfgrass management. Data suggest that the lowest ASD operational height should be employed to partially mitigate drift and droplet evaporation while improving weed control. Lower operational heights, however, reduce effective swath width and increase heterogeneity of the deposition pattern. Future research should evaluate possible engineering controls for these problems.
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    Biology and Control of Eastern Black Nightshade, Palmer Amaranth, and Common Pokeweed, in No-Till Systems on the Eastern Shore Regions of Virginia and Maryland
    Vollmer, Kurt Matthew (Virginia Tech, 2014-12-05)
    Eastern black nightshade, Palmer amaranth, and common pokeweed are three hard to control weed species on the Eastern Shore regions of Virginia and Maryland. Herbicide resistance and lack of herbicide efficacy further complicate the job of controlling these weeds. Studies were conducted on each of these weeds in order to determine herbicide efficacy and potential herbicide resistance. In addition, the translocation and metabolism of 14C-glyphosate was studied in common pokeweed. This research identified a population of eastern black nightshade that was differentially sensitive to families of ALS-inhibiting herbicides, with tolerance to members of the sulfonylurea family, but controlled with herbicides of the imidazolinone family. A population of Palmer amaranth was found to be glyphosate-resistant, but herbicide programs were identified that could control this biotype in soybean and corn systems. Experiments on the fate of glyphosate in common pokeweed indicated that glyphosate does not readily translocate from treated foliage to other plant parts, which may contribute to shoot regeneration from taproots following glyphosate treatment. Taken together, this research highlights the important weed control issues, including resistant and perennial weeds in agronomic crops that have arisen in Eastern Shore agriculture. This work will help growers to better assess their particular control issues, and take appropriate steps to mitigate any problems.
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    Characterizing Oxadiazon Resistance and Improving Postemergence Control Programs for Goosegrass (Eleusine indica) in Bermudagrass (Cynodon spp.)
    Cox, Michael Christopher (Virginia Tech, 2014-04-16)
    Goosegrass is a problematic weed of golf courses, sports fields, and residential lawns that decreases playability and aesthetic quality of turf. With the recent banning of MSMA in sports fields and intensive restrictions in golf and sod production, turfgrass managers are seeking alternatives for postemergence goosegrass control and how to utilize currently labeled goosegrass control products more effectively. Studies were conducted to investigate a suspected-resistant (SR) goosegrass accession in Richmond, VA and characterize the resistance mechanism if present. The SR accession showed a hypersensitive response to oxadiazon treatment and reached maximum electrolyte leakage quicker than the susceptible (S) accession, but had significantly lower electrolyte leakage indicating less tissue damage and suggesting there is a physiological resistance mechanism within the SR accession. In absorption and translocation studies, percent oxadiazon absorption and translocation was not significantly affected by goosegrass biotype. Roots of both the S and resistant (R) biotypes contained over 95% of total detected oxadiazon, while the plant tissue above the treated foliage only contained small quantities. These results suggest that absorption or translocation is not the mechanism conferring oxadiazon resistance in the goosegrass biotype from Richmond, VA. Greenhouse and field trials were conducted to determine the lowest rate at which topramezone, with or without the addition of triclopyr, controls goosegrass while maintaining commercially-acceptable bermudagrass quality. In field trials, topramezone rate did not significantly affect goosegrass cover at 56 and 70 days after initial treatment (DAIT). All treatments reduced goosegrass cover below 3 and 7% with and without the addition of triclopyr, respectively at 70 DAIT. A significant herbicide effect on bermudagrass cultivar showed higher injury from topramezone within three weeks of application, but injury persisted longer from treatments containing triclopyr. Bermudagrass cultivars completely recovered by 4 weeks after treatment (WAT) from all treatments. Greenhouse trials were conducted to determine if goosegrass growth stage affects efficacy of nine postemergent herbicides or programs documented to have goosegrass activity. As goosegrass growth stage increased from four- to five-leaf to greater than eight-tiller stage, goosegrass control and biomass reduction decreased among all of the herbicides except topramezone and MSMA plus metribuzin at 4 and 8 WAT. These data suggest that one application of sulfentrazone is only effective for seedling stage (pre-tiller) goosegrass control; foramsulfuron, topramezone, and metribuzin suppress all growth stages of goosegrass; and diclofop, sulfentrazone plus metribuzin, fenoxaprop, and metamifop control up to three-tiller stage goosegrass.
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    Chemical and biological control of silvery threadmoss on creeping bentgrass putting greens
    Post, Angela R. (Virginia Tech, 2013-07-31)
    Silvery threadmoss is a problematic weed of golf putting greens, growing interspersed with turf, decreasing aesthetic quality and playability.  Moss is typically controlled postemergence and currently only one herbicide, carfentrazone, is registered for silvery threadmoss control on greens.  Carfentrazone controls moss up to 75% applied at a three week interval throughout the growing season.  Alternatives providing longer residual or more effective control are desirable.  Studies were conducted to examine the growth of moss gametophytes from spores and bulbils and to evaluate turf protection products for pre and postemergence moss control.  Moss gametophytes develop best from spores at 30"aC and from bulbils at 23"aC.  Products which control moss equivalent to carfentrazone (>70%) both pre and postemergent include sulfentrazone, saflufenacil, flumioxazin, oxadiazon, and oxyfluorfen.  Fosamine and fosetyl-Al alone controlled moss equivalent to carfentrazone post-, but not preemergent.  14C glyphosate absorption and translocation through moss colonies was examined from 12 to 192 hours after treatment (HAT) to understand how herbicides are absorbed by silvery threadmoss.  It appears that 14C reaches equilibrium by 24 HAT in capillary water of the moss colony and inside moss tissues.  Subsequently, 14C is lost to the system presumably through microorganism degradation of 14C glyphosate in capillary water.  The final objective of this work was to identify and evaluate two fungal organisms observed to cause disease of silvery threadmoss on putting greens in efforts to develop a biological control.  The organisms were identified by morphology and ITS sequence as Alternaria sp. and Sclerotium rolfsii.  Alternaria sp. causes a leaf disease of silvery threadmoss and Sclerotium rolfsii causes Southern blight of silvery threadmoss.  Host specificity testing demonstrated moderate pathogenicity of S. rolfsii to annual bluegrass but not to "¥Penn A4"" creeping bentgrass.  Both organisms have potential to be effective biological controls for silvery threadmoss; however, host specificity indicates Alternaria sp. may be a better choice.  Data from these experiments suggest herbicides in two chemical classes control mosses both pre and postemergence, and sulfentrazone, fosetyl-Al, and Alternaria sp. may be new alternatives to carfentrazone for use on golf putting greens.  
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    Comparing Digital and Visual Evaluations for Accuracy and Precision in Estimating Tall Fescue Brown Patch Severity
    Sykes, Virginia R.; Horvath, Brandon J.; Warnke, Scott E.; Askew, Shawn D.; Baudoin, Antonius B.; Goatley, James M. (2017-11)
    Brown patch (Rhizoctonia solani Kuhn), a destructive disease of tall fescue (Festuca arundinacea Schreb.), is typically evaluated visually. The subjectivity of visual evaluations may be reduced using technology like digital image analysis (DIA). This study compared DIA and visual evaluations for accuracy and precision of brown patch ratings of glasshouse grown tall fescue plants. Across four experiments, 112 plants were inoculated with R. solani. Disease was rated visually and using DIA-WP (digital image analysis whole plant canopy). In two experiments, disease evaluations were replicated using three images and three visual evaluations per pot. Absolute error was calculated as the difference between actual disease severity [calculated using an individual leaf DIA method previously quantified as highly predictive of actual brown patch disease severity on tall fescue (r(2) = 0.99)] and DIA-WP and visual evaluations, respectively. Standard deviations within repeated measures were also calculated. A mixed-model ANOVA was used to determine differences (P < 0.05) in mean absolute error and mean standard deviation by method, disease range, and method by disease range. Disease ranged from 0 to 100%. Mean absolute error did not differ between methods but did by disease range, exhibiting a bell-shaped curve from 0% to 100% disease severity. Mean standard deviation exhibited significant method by disease range interaction. Mean standard deviation did not differ across the disease range within DIA-WP evaluations but did across the disease range within visual evaluations. The more consistent precision of DIA across the disease range could reduce variability in brown patch evaluations of tall fescue.
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    Differential Response of a Virginia Common Lambsquarters (Chenopodium album) Collection to Glyphosate
    Hite, Grace Ann (Virginia Tech, 2008-04-29)
    The purpose of this research was to evaluate a common lambsquarters (Chenopodium album) collection from Westmoreland County, Virginia, which exhibited a differential response to glyphosate treatments as compared to most other common lambsquarters. Plants from this site that survived glyphosate applications were collected in both 2002 and 2004. Greenhouse studies were conducted on F1, F2, and F3 progeny from this collection and compared to a wild type collection from Montgomery County, Virginia. Evaluations were conducted on these plants treated with a range of glyphosate rates. F1 progeny of the Westmoreland plants from both 2002 and 2004 collections showed reduced response to glyphosate relative to the Montgomery collection. Vigor reduction of F1 progeny from three 2004 Westmoreland source plants with 0.84 kg ae/ha of glyphosate ranged from 66 to 85% at 28 days after treatment (DAT), compared to 89% for the Montgomery collection. Evaluation of four Westmoreland F2 common lambsquarters lines derived from 2002 collections indicated significant differences in glyphosate sensitivity. Fifteen F2 lines were generated from 2004 collections from each of three Westmoreland source plants and from the Montgomery source. For the least sensitive Westmoreland source, vigor reduction ranged from only 24 to 36% across F2 lines in response to 1.68 kg/ha of glyphosate at 28 DAT, relative to 55 to 100% for the Montgomery source. I50 estimates for fresh weight reduction were 0.91 and 0.32 kg/ha, for these sources, respectively. Sequential treatments of 0.42, 1.26, and 1.68 kg/ha applied at three-week intervals to the least susceptible 2004 Westmoreland F2 line resulted in only 37% vigor reduction and no mortality among 360 treated plants. Growth chamber studies were also conducted on the F2 progeny of these sources to determine if differential growth responses occur in noncompetitive environments and in the absence of glyphosate treatment. Generally, few differences were observed among the Westmoreland and Montgomery collections in growth parameters including height, leaf number, leaf area, leaf size, shoot weight, and reproductive output. However, significant differences were observed with regard to root weight, root length, and root density. In germination studies, it was determined that the Montgomery source had significantly faster and greater seed germination than the Westmoreland source. The susceptibility of F3 seedlings to glyphosate varied significantly with respect to F2 parent line and glyphosate rate. Mortality of 100% was observed in F3 seedlings from the Montgomery source in response to the 3.36 kg ae/ha glyphosate rate, while no mortality was observed in Westmoreland F3 seedlings in response to this glyphosate rate.
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    Does NDVI consistently assess plant response to herbicides?
    Koo, Daewon; Vahidi, Milad; Gonçalves, Clebson G.; Peppers, John M.; Shafian, Sanaz; Askew, Shawn D. (2022-11-08)
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    Ecology and niche characterization of the invasive ornamental grass Miscanthus sinensis
    Dougherty, Ryan Fitzgerald (Virginia Tech, 2013-06-12)
    The recent trend in bioenergy feedstock development focuses on the use of large-statured perennial grasses that pose a relatively high risk of becoming invasive species due to the similarity in desirable agronomic traits with those of many of our worst invaders. Thus, it would be prudent to evaluate the potential ecological benefits and consequences of widespread cultivation of potentially invasive species. Miscanthus sinensis and its sterile daughter species, Miscanthus × giganteus, are two prominent bioenergy feedstock candidates due to their low input requirements and significant biomass production in a broad range of growing conditions. Despite being an extremely popular ornamental grass, and naturalizing in over half of US states, little is actually known about the biology, ecology and niche requirements of M. sinensis. Thus, the objective of our research is to characterize extant M. sinensis populations, and evaluate the niche requirements, especially in terms of the commonly limiting resources of light and soil moisture. In order to better assess the risk of M. sinensis (and subsequently M. × giganteus) cultivation, we surveyed 18 naturalized populations across the east coast to characterize habitat preferences, population structure, and plant performance across a latitudinal gradient. We found the vast majority of M. sinensis populations occurred in areas of high and low resource availability (e.g. soil nutrients and light) along roadsides and forest edges, with outlier individuals found in forest understories. We conducted a greenhouse study to compare shade and soil moisture tolerance among common ornamental cultivars and naturalized populations, where we found enhanced plant growth and vigor in naturalized biotypes compared to ornamentals across varying levels of shade. We also found that both naturalized and ornamental biotypes were not significantly affected by soil moisture stress, and thus express significant drought tolerance. Finally, we investigated the temperature and moisture requirements of M. sinensis seeds and determined a base temperature of approximately 8"C, as well as variable moisture and time to germination requirements between varieties and seed sources. These basic ecological studies will help refine and support future evaluations and weed risk assessments of both Miscanthus sinensis and M. × giganteus, which is critical in prevention of major ecological invasions.
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    The Effect of Fe-sulfate on Annual Bluegrass, Silvery Thread Moss, and Dollar Spot Populations Colonizing Creeping Bentgrass Putting Greens
    Reams, Nathaniel Frederick (Virginia Tech, 2013-06-05)
    Annual bluegrass (Poa annua L.) is the most problematic weed to control in creeping bentgrass (Agrostis stolonifera L.) putting greens.  The objective of this study was to transition a mixed putting green stand of annual bluegrass and creeping bentgrass to a monoculture by using fertilizers and plant growth regulators that selectively inhibit annual bluegrass.  A 25 year old loamy sand rootzone research green, planted with \'Penn-Eagle\' creeping bentgrass, with roughly 45% initial annual bluegrass coverage was utilized.  The biweekly application of ammonium sulfate (4.8 kg ha-1) with treatments of ferrous sulfate at rates of 0, 12.2, 24.4, and 48.8 kg ha-1 and in combination with seaweed extract (12.8 L ha-1) or paclobutrazol (0.37 L ai ha-1 spring and fall; 0.18 L ai ha-1 summer) were applied March to October, 2011 and 2012.  Plots receiving the highest rate of ferrous sulfate resulted in annual bluegrass infestation declines from an early trial amount of 45% to a final average of 20% but also resulted in unacceptable late-summer events of annual bluegrass collapse.  The ferrous sulfate medium rate resulted in a smooth transition from early-trial annual bluegrass infestation of 45% to an end of trial infestation of 20% and had the highest putting green quality.  Previous research has reported that consistent use of paclobutrazol can effectively and safely reduce annual bluegrass infestations.  In this trial annual bluegrass was reduced to 9% infestation after three months of application.  Two unexpected observations from this trial were that ferrous sulfate, applied at medium to high rates, significantly reduced silvery thread moss (Bryum argentum Hedw.) populations and occurrences of dollar spot (Sclerotinia homoeocarpa F. T. Bennett) disease.  Dollar spot control with ferrous sulfate has not previously been reported in the literature, so additional studies were designed to investigate this phenomenon further.  A creeping bentgrass putting green study was conducted to determine if sulfur, iron, or the two combined as ferrous sulfate decreases dollar spot activity.  Ferrous sulfate resulted in the highest turf quality and suppressed S. homoeocarpa infection, even during high disease pressure.  Fe-EDTA suppressed dollar spot infection as well as ferrous sulfate but quality declined to unacceptable levels during the summer, due to Fe-EDTA only.  Sulfur did not affect or increased S. homoeocarpa infection, indicating that a high and frequent foliar rate of iron is responsible for dollar spot control.  An in-vitro study was conducted to determine if agar pH in combination with iron concentrations affects mycelial growth of S. homoeocarpa.  Results from this trial indicated that 5.4 agar pH is an optimal pH for mycelial growth.  The 10 to 100 mg iron kg-1 concentration had little effect on mycelial growth at 5.0 and 5.5 pH, but increased growth at 4.5 and 6.5 pH.  As the iron concentration was increased from 10 to 100 to 1000 mg kg-1, mycelial growth decreased or stopped.  Our final conclusions are that seasonal biweekly foliar applications of the medium rate of ferrous sulfate (24.4 kg ha-1) safely and effectively reduced annual bluegrass infestation out of a creeping bentgrass putting green, while also effectively suppressing silvery thread moss and dollar spot incidence.
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    Effect of temperature and heat units on zoysiagrass response to herbicides during post-dormancy transition
    Craft, Jordan M.; Godara, Navdeep; Brewer, John R.; Askew, Shawn D. (Cambridge University Press, 2023-04)
    In the transition zone, turfgrass managers generally utilize the dormancy period of warm-season turfgrass to apply herbicides for managing winter annual weeds. Although this weed control strategy is common in bermudagrass [Cynodon dactylon (L.) Pers.], it has been less adopted in zoysiagrass (Zoysia spp.) due to variable turfgrass injury during post-dormancy transition. Previous research reported that air temperature could affect weed control and crop safety from herbicides. Growth-chamber studies were conducted to evaluate zoysiagrass response to glyphosate and glufosinate as influenced by three different temperature regimes during and after treatment. A field research study was conducted at four site-years to assess the influence of variable heat-unit accumulation on zoysiagrass response to seven herbicides. In the growth-chamber study, glufosinate injured zoysiagrass more than glyphosate and reduced time to reach 50% green cover reduction, regardless of the rate, when incubated for 7 d under different temperature levels. When green zoysiagrass sprigs were incubated for 7 d at 10 C, the rate of green cover reduction was slowed for both herbicides; however, green cover was rapidly reduced under 27 C. After treated zoysiagrass plugs having 5% green cover were incubated at 10 C for 14 d, glyphosate-treated plugs reached 50% green cover in 22 d, similar to nontreated plugs but less than the 70 d required for glufosinate-treated plugs. Zoysiagrass response to glyphosate was temperature dependent, but glufosinate injured zoysiagrass unacceptably regardless of temperature regime. Diquat, flumioxazin, glufosinate, and metsulfuron + rimsulfuron injured zoysiagrass at 200 or 300 growing-degree days at base 5 C (GDD(5C)) application timings, but foramsulfuron and oxadiazon did not injure zoysiagrass regardless of GDD(5C). The relationship of leaf density to green turf cover is dependent on zoysiagrass mowing height, and both metrics are reduced by injurious herbicides. Research indicates that glufosinate injures zoysiagrass more than glyphosate, and the speed and magnitude of herbicide injury generally increase with temperature.
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    Elucidating Influence of Temperature and Environmental Stress on Turfgrass Response to Mesotrione and Evaluation of Potential Synergistic Admixtures to Improve Mesotrione Efficacy
    Ricker, Daniel (Virginia Tech, 2006-12-14)
    Mesotrione is under evaluation for registration in turfgrass for weed control, but often requires repeat treatments. Previous research in agricultural crops indicates tank mixtures with mesotrione may improve weed control. Three field trials were conducted in 2005 and 2006 in Blacksburg, VA on smooth crabgrass in perennial ryegrass and tall fescue. Data indicate mesotrione applied in combination with bentazon, bromoxynil, or carfentrazone, controlled smooth crabgrass better than any of these herbicides applied alone at all sites. Adding mesotrione to MSMA and quinclorac improved smooth crabgrass on of three sites. Sequential mesotrione applications improved long term weed control.
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    Environmental Best Management Practices for Virginia's Golf Courses
    Schoenholtz, Stephen H.; Goatley, Michael; Ervin, Erik H.; Hodges, Steven C.; Hipkins, Perry L.; McCall, David S.; Askew, Shawn D.; Youngman, Roger R.; Hipkins, Patricia A.; Grisso, Robert D.; Muckley, Glenn; George, Lester; Ballard, Mike; Roadley, Chuck; Lajoie, Matt; Rodriguez, Mark; Habel, Robert; Sexton, Tim; Buchen, Terry (Virginia Cooperative Extension, 2019-01-09)
    Provides recommendations for Virginia golf courses, emphasizing water quality protection.
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    Environmental Best Management Practices for Virginia's Golf Courses
    Schoenholtz, Stephen H.; Goatley, Michael; Ervin, Erik H.; Hodges, Steven C.; Hipkins, Perry L.; McCall, David S.; Askew, Shawn D.; Youngman, Roger R.; Hipkins, Patricia A.; Grisso, Robert D.; Muckley, Glenn; George, Lester; Ballard, Mike; Roadley, Chuck; Lajoie, Matt; Rodriguez, Mark; Habel, Robert; Sexton, Tim (Virginia Cooperative Extension, 2013-02-27)
    Provides recommendations for golf courses in the Commonwealth that emphasize water quality protection and have been specifically adapted for courses in Virginia using the results of current research, the experience of golf course superintendents in implementing best management practices, golf industry representatives, and state regulators.
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    Epigenetic Responses of Arabidopsis to Abiotic Stress
    Laliberte, Suzanne Rae (Virginia Tech, 2023-03-17)
    Weed resistance to control measures, particularly herbicides, is a growing problem in agriculture. In the case of herbicides, resistance is sometimes connected to genetic changes that directly affect the target site of the herbicide. Other cases are less straightforward where resistance arises without such a clear-cut mechanism. Understanding the genetic and gene regulatory mechanisms that may lead to the rapid evolution of resistance in weedy species is critical to securing our food supply. To study this phenomenon, we exposed young Arabidopsis plants to sublethal levels of one of four weed management stressors, glyphosate herbicide, trifloxysulfuron herbicide, mechanical clipping, and shading. To evaluate responses to these stressors we collected data on gene expression and regulation via epigenetic modification (methylation) and small RNA (sRNA). For all of the treatments except shade, the stress was limited in duration, and the plants were allowed to recover until flowering, to identify changes that persist to reproduction. At flowering, DNA for methylation bisulfite sequencing, RNA, and sRNA were extracted from newly formed rosette leaf tissue. Analyzing the individual datasets revealed many differential responses when compared to the untreated control for gene expression, methylation, and sRNA expression. All three measures showed increases in differential abundance that were unique to each stressor, with very little overlap between stressors. Herbicide treatments tended to exhibit the largest number of significant differential responses, with glyphosate treatment most often associated with the greatest differences and contributing to overlap. To evaluate how large datasets from methylation, gene expression, and sRNA analyses could be connected and mined to link regulatory information with changes in gene expression, the information from each dataset and for each gene was united in a single large matrix and mined with classification algorithms. Although our models were able to differentiate patterns in a set of simulated data, the raw datasets were too noisy for the models to consistently identify differentially expressed genes. However, by focusing on responses at a local level, we identified several genes with differential expression, differential sRNA, and differential methylation. While further studies will be needed to determine whether these epigenetic changes truly influence gene expression at these sites, the changes detected at the treatment level could prime the plants for future incidents of stress, including herbicides.