Search

Annual grassy weeds are problematic in intensively managed turfgrass systems due to a lack of selective and affordable control options. Four projects were conducted from 2020-2023 to evaluate novel techniques for Annual bluegrass (Poa annua L.), goosegrass (Eleusine indica L. Gaertn.), and smooth crabgrass (Digitaria ischaemum Schreb.) control on golf course putting greens or putting green surrounds. Hybrid bermudagrass Cynodon transvaalensis Burtt. Davy. x dactylon L. Pers.) tolerated cumyluron regardless of application timing, endothall when applied during full dormancy, and methiozolin when applied during mid-transition. Methiozolin half-life in the upper 2-cm of 12 hybrid bermudagrass putting greens was approximately 14 days and was prolonged in similar studies by seven orders of magnitude when herbicide was applied to bare ground compared to adjacent Kentucky bluegrass (Poa pratensis L.) turf. In a study conducted in Alabama, California, Florida, and Virginia, methiozolin at labeled use rates applied biweekly controlled smooth crabgrass >80% in creeping bentgrass (Agrostis stolonifera L.) and hybrid bermudagrass turf. Although similar programs also controlled goosegrass, acceptable control required more applications than are allowed on the product label. Targeted application devices (TAD), such as spot sprayers and dabbers that are used for individual plant treatment of escaped weeds, were tested for uniformity of fluid delivery. Fluid output of dabbing devices was highly variable and dependent on reservoir fill level, reservoir air seal, human user, and contact time, but largely independent of peak force exerted during the dabbing event. These studies suggest that new products are available to improve annual grassy weed control in turfgrass systems, but proper application timing and device calibration is important to achieve best results.

Thermal imaging is a developing tool that can help turf managers reduce water consumption and improve irrigation scheduling, but in-depth studies are needed to maximize this potential. This study evaluated the ability of thermal imaging to identify water stress in a creeping bentgrass (Agrostis stolonifera ‘007’) putting green. Water use and canopy temperature (Tc) were measured for plots subjected to three levels of measured water replacement (full, half, and none) to evaluate changes over a range of soil water potentials (SWP). Water use was consistent across the irrigation treatments up to several days before observed wilt with crop coefficients (Kc) between 0.83-1.01. As drought conditions progressed (SWP c decreased. Segmented linear regression was used to quantify the trends and identify the critical value of -1501 kPa. Various metrics utilizing Tc were evaluated for a response to water stress. Two metrics, standard deviation of Tc and Tc relative to non-water stressed turf, show potential to indicate periods of stress prior to visible wilt. A strong diurnal pattern was observed in all Tc metrics confirming the need to normalize Tc for current weather conditions. Multiple regression using 2018 data was used to develop a model using weather parameters of air temperature, solar radiation, relative humidity, and wind speed to estimate Tc values of a non-water stressed baseline. A two parameter model using air temperature and solar radiation input provided a strong fit (adjusted R2=0.955) and when applied to unpublished dataset from a 2016 study measuring Tcon a creeping bentgrass putting green. This study shows water use remained consistent until SWP reached a wilting point, followed by a sharp decrease in water use approaching Kc of zero. We show that metrics utilizing Tc can be early indicators of water stress in turfgrass. However, further research with different microclimates and plot sizes would be needed to identify specific values of these metrics that quantify water stress. We also describe a multiple regression model to predict Tc of non-water stressed baseline under various weather conditions. Understanding how Tc of turf with no water stress behaves in different weather can improve identification of water stress. Advisor: William C. Kreuser

Goosegrass [Eleusine indica (L.) Gaertn.] and smooth crabgrass [Digitaria ischaemum (Schreb.) Schreb. ex Muhl.] are problematic weeds in bermudagrass and creeping bentgrass turf. Increased incidences of herbicide resistant weed populations and severe use restrictions on formerly available herbicides have increased need for selective, postemergence control options for these weeds in creeping bentgrass and bermudagrass turf. This weed management exigency has led turf managers to utilize less effective, more expensive, and more injurious options to manage goosegrass and smooth crabgrass. Although potentially injurious, topramezone can control these weeds, especially goosegrass, at low doses. Low-dose topramezone may also improve bermudagrass and creeping bentgrass response. An initial investigation of three 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibiting herbicides in different turf types showed that Kentucky bluegrass, perennial ryegrass, and tall fescue were highly tolerant to topramezone, while creeping bentgrass and bermudagrass could tolerate topramezone doses that may control grassy weeds. Further investigation suggested that frequent, low-dose topramezone applications or metribuzin admixtures could enhance weed control and may conserve turfgrass quality. A novel mixture of topramezone at 3.7 g ae ha-1 and metribuzin at 210 g ai ha-1 controlled goosegrass effectively and reduced bermudagrass foliar bleaching associated with topramezone 10-fold compared to higher doses of topramezone alone in 19 field and 2 greenhouse trials. In an attempt to further enhance bermudagrass tolerance to topramezone, post-treatment irrigation was applied at various timings. When bermudagrass turf was irrigated with 0.25-cm water at 15 or 30 minutes after herbicide treatment, bermudagrass injury was reduced to acceptable levels when following low-dose topramezone plus metribuzin but not when following high-dose topramezone alone. Goosegrass control was reduced significantly by post-treatment irrigation in all cases, while irrigation reduced goosegrass control by low-dose topramezone plus metribuzin to below-commercially-acceptable levels. Novel, low-dose, frequent application programs containing topramezone or siduron were developed for season-long crabgrass or goosegrass control on creeping bentgrass greens. Greens-height creeping bentgrass quality was preserved following five biweekly treatments of siduron at rates between 3,400 to 13,500 g ai ha-1 and topramezone at 3.1 g ha-1. Siduron programs controlled smooth crabgrass and suppressed goosegrass while topramezone programs controlled goosegrass and suppressed smooth crabgrass. In laboratory and controlled-environment experiments, goosegrass absorbed three times more 14C than bermudagrass within 48 hours of 14C-topramezone treatment. Bermudagrass also metabolized topramezone twice as fast as goosegrass. Metribuzin admixture reduced absorption by 25% in both species. When herbicides were placed exclusively on soil, foliage, or soil plus foliage, topramezone controlled goosegrass only when applied to foliage and phytotoxicity of both bermudagrass and goosegrass was greater from topramezone than from metribuzin. Metribuzin was shown to reduce 21-d cumulative clipping weight and tiller production of both species while topramezone caused foliar discoloration to newly emerging leaves and shoots with only marginal clipping weight reduction. These data suggest that selectivity between bermudagrass and goosegrass is largely due to differential absorption and metabolism that reduces bermudagrass exposure to topramezone. Post-treatment irrigation likely reduces topramezone rate load with a concomitant effect on plant phytotoxicity of both species. Metribuzin admixture decreases white discoloration of bermudagrass by decreased topramezone absorption rate and eliminating new foliar growth that is more susceptible to discoloration by topramezone.

Light is one of the primary growth-limiting factors of turfgrass. Without sufficient quantities of photosynthetically active radiation (PAR; 400-700 nm wavelength), turfgrass quality will decline and could ultimately result in plant death. PAR light can be expressed in a daily quantity known as the daily light integral (DLI) and has been utilized to determine minimum light requirements for turfgrass as well as other plants. With an estimated 25% of all turfgrass being maintained under some level of shaded conditions, it is imperative to define minimum DLI requirements of various turfgrass systems to ensure acceptable turf quality. In addition, it is necessary to evaluate novel methods of quantifying and assessing light conditions so that turfgrass managers can direct appropriate agronomic decisions. This research aims to determine a minimum DLI requirement of a creeping bentgrass putting green, evaluate an efficient quantification method of DLI requirements for multiple warm season turfgrasses in an established landscape, and to estimate PAR reduction with total visible light measuring devices under various tree species. After evaluation of creeping bentgrass putting green turfgrass quality and coverage under 0, 70, 80, and 90% shade for two years, a minimum DLI requirement was estimated to be 30 mol m-2 d-1. In a controlled research setting over two years, minimum DLI requirements of four warm season turf types, ‘Astro-DLM’ bermudagrass, common bermudagrass, ‘Cavalier’ zoysiagrass, and ‘Meyer’ zoysiagrass, were determined to be 20.4, 25.9, 15.0, and 21.1 mol m-2 d-1, respectively. However, an efficient method to determine DLI requirements in an established golf course landscape was able to accurately estimate DLI requirements for just two of the four warm season turf types and further evaluation is needed. PAR reduction beneath tree shade canopies varied among tree species, but was not able to be estimated from visible light measurements with sufficient precision. This results of this research establishes minimum DLI requirements of popular turfgrass selections for turfgrass managers to utilize as a baseline when making agronomic decisions in shaded conditions. Additionally, alternate methodology is evaluated to efficiently and accurately estimate minimum DLI requirements.

Annual bluegrass (Poa annua L.) and roughstalk bluegrass (Poa trivialis L.) are among the most troublesome grass weeds on golf courses throughout the United States. Herbicides for selective control of these weeds in cool-season fairways are limited and ineffective. Methiozolin is a new isoxazoline herbicide that controls annual bluegrass on putting greens and shows promise for possible weed control in fairways. Kentucky bluegrass (Poa pratensis L.) is among the most common turfgrass species used for golf fairways in the Northern United States and its response to methiozolin has scarcely been tested. A 2.5-yr field study was conducted at four Virginia locations to evaluate methiozolin efficacy for selective annual bluegrass and roughstalk bluegrass control in creeping bentgrass (Agrostis stolonifera L.) or Kentucky bluegrass fairways. Another study evaluated the response of 110 Kentucky bluegrass varieties to three rates of methiozolin. Annual bluegrass has long been presumed to impact putting green trueness, or the ability of the greens canopy to provide a smooth and directionally-consistent ball roll. Although much research has evaluated the impact of greens management on ball roll distance, no peer-reviewed research has evaluated how canopy surface factors, such as weedy annual bluegrass, will influence ball roll direction. Laboratory and field research was conducted to elucidate and overcome experimental errors that may be limiting assessment of ball directional imprecision caused by greens canopy anomalies. Techniques to minimize experimental error were employed in field studies at two Virginia golf courses to determine the influence of annual bluegrass on ball directional imprecision, bounce, and acceleration. Study results suggest that annual bluegrass patches in a creeping bentgrass putting surface can cause subtle increases in ball directional imprecision and bounce but several sources of error must be controlled before these effects can be measured. By using a mechanical putter to avoid directional errors associated with simulated-putt devices, selecting golf balls with balanced centers of gravity, eliminating legacy or "tracking" effects of repeated ball rolls via canopy brushing, and scoring ball direction 30 cm prior to terminal acceleration, we were able to detect an increase in ball directional imprecision of 8 mm m⁻¹ when balls rolled over a single patch of annual bluegrass compared to adjacent rolls on visually-pure creeping bentgrass. In herbicide efficacy studies, methiozolin-only treatments did not significantly injure creeping bentgrass or Kentucky bluegrass, reduce quality, or reduce normalized difference vegetative index regardless of application timings and rates. In general, fall applications of methiozolin reduced roughstalk bluegrass and annual bluegrass cover more than the spring-only treatments. At 1 year after the last treatment, methiozolin at 1500 g ha⁻¹ applied four times in fall at 2-wk intervals for two consecutive years controlled roughstalk bluegrass and annual bluegrass ≥85% and more consistently than other herbicides or treatment regimes. Spanning 110 Kentucky bluegrass varieties, a commercially-acceptable threshold of 30% Kentucky bluegrass injury required between 3.4 to more than 10 times the methiozolin rate needed for annual bluegrass control. Results indicate that annual bluegrass increases directional imprecision and bounce of golf balls rolling across a greens canopy. Methiozolin could be a viable herbicide for managing annual and roughstalk bluegrass in Kentucky bluegrass and creeping bentgrass fairways but weed control efficacy may be dependent on application timing. By measuring small differences in ball directional imprecision as influenced by greens canopy factors, future research efforts will aim to help turf managers choose appropriate greens management techniques.

Light reflectance from plants can be used as a non-invasive predictor of health and yield for many cropping systems, and has been investigated to a lesser extent with managed turfgrass systems. The frequent agronomic inputs associated with maintaining golf course grasses allow for exceptional stand quality under harsh growing conditions, but often expend resources inefficiently, leading to either stand loss or unnecessary inputs in localized areas. Turfgrass researchers have adopted some basic principles of light reflectance formerly developed for cropping systems, but field radiometric-derived narrow-band algorithms for turfgrass-specific protocols are lacking. Research was conducted to expand the feasibility of using radiometry to detect various turfgrass stressors and improve speed and geographic specificity of turfgrass management. Methods were developed to detect applied turfgrass stress from herbicide five days before visible symptoms developed under normal field growing conditions. Soil volumetric water content was successfully estimated using a water band index of creeping bentgrass canopy reflectance. The spectral reflectance of turfgrass treated with conventional synthetic pigments was characterized and found to erroneously influence plant health interpretation of common vegetation indices because of near infrared interference by such pigments. Finally, reflectance data were used to estimate root zone temperatures and root depth of creeping bentgrass systems using a gradient of wind velocities created with turf fans. Collectively, these studies provide a fundamental understanding of several turfgrass-specific reflectance algorithms and support unique opportunities to detect stresses and more efficiently allocate resources to golf course turf.

Annual bluegrass is a winter annual grass that is problematic on golf putting greens due to its light green color, prolific seedhead production and intolerance to stress. On creeping bentgrass putting greens, herbicides for annual bluegrass control are limited. A new herbicide, methiozolin, developed by Moghu Research Center, LLC, in Daejeon, South Korea, safely and selectively controls annual bluegrass in creeping bentgrass and several other turfgrass species. Methiozolin typically controls annual bluegrass over several weeks, allowing desirable turfgrass time to grow into areas previously infested by annual bluegrass with little surface disruption. The mode of action of methiozolin is unknown, but has been proposed to act as either a cell wall biosynthesis inhibitor (CBI) or an inhibitor of tyrosine aminotransferase (TAT). Field studies were conducted at Virginia Tech to investigate strategies promoting surface recovery on putting greens following atypically rapid annual bluegrass loss resulting from methiozolin application, intensive core-cultivation as well as potential interactions with plant growth regulators (PGR's), like ethephon. In the rapid annual bluegrass removal study, all treatments receiving additional fertility via synthetic fertilizer with or without trinexapac-ethyl or biostimulant recovered 1 to 3 weeks more quickly than treatments that did not include additional fertility. Addition of the PGR trinexapac-ethyl inconsistently regulated speed of canopy recovery, both increasing and decreasing recovery speed. Under normal maintenance conditions, methiozolin does not negatively influence putting green recovery, however, if the putting green is exposed to droughty conditions, methiozolin can reduce recovery time by several weeks. Core-cultivation should be avoided in conjunction with methiozolin and ethephon applications because when this procedure was conducted on the same day as herbicide application it significantly damaged creeping bentgrass, reducing cover to 19% at 2000 g ai ha⁻¹, compared to the non-treated at 62%. Regarding the question of methiozoling mode of action, laboratory studies supported the claim that addition of exogenous 4-hydroxyphenylpyruvate (4-HPP) alleviates symptoms of methiozolin exposure in lesser duckweed, a model monocot species, but feeding various turfgrass species and annual bluegrass exogenous 4-HPP did not alleviate symptoms. Creeping bentgrass secondary root length and density was not affected by methiozolin, although annual bluegrass, Kentucky bluegrass and perennial ryegrass secondary root lengths were reduced. Based on these data, it does not appear that TAT inhibition is a primary mode of action of methiozolin in turfgrass. Studies were conducted to determine if methiozolin inhibited cell wall biosynthesis in desirable turfgrass species and annual bluegrass. All species exhibited decreased enrichment of ¹³C in cell-wall sugars form ¹³C-glucose in response to methiozolin and a known cell wall biosynthesis inhibitor, indaziflam. Indaziflam and methiozolin at 0.01 µM inhibited ¹³C enrichment of all sugars less than methiozolin at 1.0 µM, for xylose, arabinose and glucose, but not galactose. Addition of 4-HPP increased incorporation of ¹³C into xylose, but had no other influence on ¹³C incorporation into other cell wall sugars. Lack of species specific response indicates that cell wall biosynthesis inhibition is probably not the source of interspecific species responses observed in the field.

Annual bluegrass (Poa annua L.) is considered the most problematic weed on golf greens because of its fecund characteristic, low heat and disease tolerance in the summer, massive seed head reproduction, and bright green color. Methiozolin was initially an herbicide for weed control in crop fields and now is being developed for annual bluegrass control on golf greens. It has shown effectiveness and safety on multiple grass species, including creeping bentgrass (Agrostis stolonifera), kentucky bluegrass (Poa pratensis), and bermudagrass (Cynodon dactylon). As a systemic herbicide, methiozolin is mainly taken up by root absorption and shows limited acropetal movement in the plant. It is recommended that methiozolin be watered in immediately after application. Nitrogen, as one of the essential elements of plants, plays an important role in the lateral growth and chlorophyll formation of creeping bentgrass, which can greatly influence the recovery rate, color, and other quality characteristics of the turfgrass surface. Digital Image Analysis (DIA) is a new method for turfgrass surface quality evaluation. DIA has shown efficiency in data analysis with an equal accuracy as the normalized difference vegetation index (NDVI) and better consistency than visual evaluation method (NTEP).Two experiments were conducted on the Ohio State University Golf Club practice green and one on a USGA green at the Ohio Turfgrass Foundation Research and Education Facility. The first project on the OSU Golf Club putting green was designed to study the interaction of methiozolin, nitrogen rate and fertilizing frequency on creeping bentgrass recovery and annual bluegrass suppression/control in the spring with fall only methiozolin treatments and fall/spring methiozolin treatments. The second project consisted of three methiozolin rates and four rates to determine the best combination of spring methiozolin rate and spring nitrogen application strategies that shows best control over annual bluegrass while benefiting creeping bentgrass recovery and safety. The third project at the OSU Research and Education Facility was to study the effects of five nitrogen rates on the lateral growth/recovery and quality of creeping bentgrass with/without methiozolin treatments. The first project found that there was no significant interaction between methiozolin, nitrogen rates and fertilizing frequency in the spring. Spring methiozolin applications had a negative effect on creeping bentgrass color and recovering rate, but also a subsequent control on annual bluegrass after methiozolin fall treatments. Among all nitrogen strategies, the 24.4 kg N ha-1 every two weeks and the 12.2 kg N ha-1 every week were the best for creeping bentgrass green-up and recovery in the spring of 2014. The second experiment project found that methiozolin rates higher than the protocol rate (0.53 kg a.i. ha-1) had significant negative effects on annual bluegrass color and significantly more decrease on annual bluegrass population. Both creeping bentgrass and annual bluegrass color increased significantly with higher nitrogen rates and 24.4 kg N ha-1 had significantly more decrease on annual bluegrass population, which means higher nitrogen rates benefits creeping bentgrass more than annual bluegrass under methiozolin treatments. The third study found that there was no significant negative effects of methiozolin on creeping bentgrass color or lateral growth. According to the regression, there was a quadratic relation between creeping bentgrass color and time. The lateral growth rate of creeping bentgrass was constant through time and was only influenced by the nitrogen rate.

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.

Photocatalytic TiO₂ [titanium dioxide] generates strong oxidative effects when illuminated with ultraviolet (UV) light with wavelengths of less than 385 nm. UVB has wavelengths ranging from 280 to 315nm. Previous research indicates the oxidative species and UVB radiation can react and cause cellular damage to microorganisms, which may reduce Sclerotinia homoeocarpa growth and help to control dollar spot disease development. The objectives of this study were to investigate the interactions of TiO₂ and UVB radiation, both in vitro and in vivo, on the growth and development of dollar spot. Factorial treatments consisting of five rates of TiO₂ and three doses of UVB radiation were arranged in a completely random design. The in vitro study showed that the mycelia linear extension of S. homoeocarpa was significantly inhibited by UV radiation. The highest UVB radiation (0.2754mol·m⁻²·day⁻¹ [mol per square meter per day]) resulted in the least mycelium growth. Regression analysis predicted that 14 days after inoculation the mycelium diameter of plates exposed to the highest UVB radiation without TiO₂ would be 27mm; while the non-treated control was predicted to be 243mm. There were no significant differences among TiO₂ rates compared to the non-treated control. Results were similar in the in vivo study where creeping bentgrass (Agrostis stolonifera L) was grown in pots in a growth chamber, and exposed to three doses of UVB radiation for 12 hours per day and 4 rates of TiO₂. The lowest UVB radiation (0.04549 mol·m⁻²·day⁻¹) treatment resulted in the largest infected area (58mm in diameter). Medium and high UVB radiation doses (0.1064 mol·m⁻²·day⁻¹ and 0.5444 mol·m⁻²·day⁻¹, respectively) reduced the infected area to 40mm and 46mm 14 days after inoculation respectively. Overall, it appears that UVB radiation may be involved in regulating the overall size of S. homoeocarpa growth, and applications photocatalytic TiO₂ may result in an increase in disease due to its UV screening capability.

Previous research has indicated that strobilurin fungicide applications may improve summer stress tolerance of creeping bentgrass (Agrostis stolonifera L.) putting greens. In this experiment, strobilurin fungicides were integrated within a summer fungicide program to evaluate disease severity and plant physiological effects. Fungicide programs were applied on a ‘Dominant Southern’ creeping bentgrass putting green; all of which consisted of five fungicide spray applications from June to August during 2011 and 2012. The 2nd and 5th application in each program consisted of a strobilurin fungicide. Strobilurin fungicides evaluated included pyraclostrobin, azoxystrobin, fluoxastrobin, or trifloxystrobin. The remaining fungicide applications were identical across programs. Measurements of visual quality, spectral reflectance, turfgrass cover, rooting characteristics, and disease severity were collected. The non-treated control was similar to treated plots in all parameters in 2011, and until 42 and 56 days after initial treatment (DAIT) the following year. At this time, fungicide programs began to exhibit greater visual quality, turfgrass cover, and spectral reflectance compared to the non-treated control. Differences in physiological effects coincided with the first observation of brown patch (Rhizoctonia Solani Kühn) in the experimental area. These data suggest that strobilurin fungicides exhibit excellent efficacy for disease control during summer, and that direct physiological effects may be transient and observable over the long term. A 2-year field experiment was conducted to determine if applications of pyraclostrobin, azoxystrobin, fluoxastrobin, and trifloxystrobin could improve plant physiological effects of a ‘Dominant Southern’ creeping bentgrass putting green in the absence of visible foliar disease. Experimental units were arranged in a split-plot randomized complete block design. A fungicide mixture containing chlorothalonil and iprodione and a no fungicide treatment served as the whole-plots. Chlorothalonil and iprodione were applied at 14-day intervals. Sub-plots were treated with strobilurin fungicides (azoxystrobin, pyraclostrobin, fluoxastrobin, and trifloxystrobin) and a non-treated control. Sub-plots were applied at 14-day intervals. Neither differences in disease severity nor any physiological effect was observed on any assessment date over the course of two years. The results of this experiment suggest that while strobilurin fungicides perform well for disease control, detectable plant physiological effects under field conditions were limited.

Creeping bentgrass is the most popular turfgrass species on golf course putting greens throughout the world due to its fine texture, recuperative ability and dense growth habit. Drought stress is an environmental induced condition that is common to turfgrasses. Foliar fertilization is a common maintenance practice that is conducted and utilized on golf course putting greens due to the reduced total input, quick response and reduced environmental impact. The cuticle of creeping bentgrass creates a hydrophobic barrier that foliar applied fertilizers need to penetrate to be used by the plant. The cuticle morphology and composition is subject to change due to the environment. Therefore, the primary objectives of this thesis were to determine how the cuticle of creeping bentgrass was affected by drought stress, understand the influence of the cuticle on foliar fertilization absorption, and investigate methods to aid foliar applications. Due to the limited literature on creeping bentgrass cuticle layer and methodology of studying the cuticle layer of grasses, a preliminary growth room study was conducted. Creeping bentgrass plugs were harvested and transplanted into a growth room where treatments were conducted. Treatments included a control with 100% ET returned and two drought treatments, where 50% and 25% ET was returned. Cuticle morphological and compositional changes were studied. Results revealed, 1–hexacosanol, comprising approximately 88% of the entire cuticle of creeping bentgrass. The remaining 12% was comprised of fatty acids, alkanes, an aldehyde and a five unknown compounds. Total wax load showed a pattern of increasing due to the drought stress. Cuticle crystalloid density increased significantly with drought stress. 15N–labeled urea was applied foliarly and % recovery was determined to evaluate the effect of drought on foliar uptake. Percent 15N recovery was significantly reduced in the two drought treatments compared to the control. The increase in total wax was negatively correlated with %15N recovery. Results suggest cuticle morphology and quantity may limit foliar fertilizer absorption. A second study was conducted investigating drought stress on creeping bentgrass cuticle and foliar absorption. Treatments included control and drought where 100% or 50% ET was returned daily for 10d. Foliar absorption was studied with 15N–labeled urea applied with or without surfactant addition. Cuticle morphology and compositional changes were studied along with % 15N recovery. Total wax and crystalloid density increased significantly due to drought treatments. This was caused mainly by an increase in primary alcohols and fatty acids. Percent 15N recovery was affected by irrigation treatment and surfactant addition. The results presented suggest that the surfactant addition allows for improved penetration or adherence to cuticles influenced by drought stress. Genetically modified plants can be engineered to tolerant environmental stresses, and could prove beneficial to regular maintenance practices. Transgenic creeping bentgrass was developed at Clemson University using the overexpression of Arabidopsis vacuolar H+–pyrophosphatase (AVP1) gene. Wild-type (WT) and transgenic (TG) cuticles were studied for differences in morphology and composition under control and drought treatments. The TG cuticle morphology was similar to the WT, but small differences were seen. Crystalloid density increased due to drought in the WT but not in the TG. Irrigation treatment had no significant effect on total cuticle wax for either WT or TG. Interestingly, the TG cuticle wax load was significantly higher (>1 μg cm–2) than the WT cuticle wax load. This was due to a larger amount of primary alcohols and fatty acids in the TG cuticle. Results suggest that the TG cuticle provides a less rough surface that would not influence a foliar applied solution, especially under drought stress where crystalloid density is not affected. Fractal analysis was used to study and classify the crystalloid shape of WT and TG creeping bentgrass. The analysis was used to related cuticle chemical composition data, crystalloid shape and the fractal dimension. It was revealed that there was a significant difference in fractal dimension for the TG and WT crystalloids. The change in fractal dimension was thought to be the TG cuticle preparing itself for stress and therefore making its cuticle more hydrophobic to create a better protection barrier.

Creeping bentgrass (Agrostis stolonifera L.) is a species commonly used in high maintenance turf areas. When grown under shade conditions, A. stolonifera becomes thin, elongated, and looses stem and root mass which ultimately leads to loss of turfgrass coverage. These responses to light stimuli are mediated, in part, by phytohormones, gibberellins. Suppression of gibberellin levels by overexpression of genes involved in their catabolism has been proven to successfully control plant stature. Gibberellin suppression also alters plant morphology and photosynthetic characteristics. The objective of this study was to determine the effect of runner bean (Phaseolus coccineus) GA2ox gene (PcGA2ox) overexpression (which increases gibberellin catabolism) on creeping bentgrass quality and performance under various light conditions and intense, short mowing height. GA2ox overexpression resulted in superior quality of Ax6549 under all shade treatments by delaying the decline of its color and coverage. Photosynthetic characterization indicated higher photosynthate supply per leaf area unit and enhanced low light use efficiency as potential factors associated with superior performance of Ax6549 under reduced light conditions. However, growth analysis data indicated lower growth efficiency and leaf productivity in Ax6549. Although this appeared to be contradictory to data obtained through photosynthetic characterization, this contradiction could be explained by increased self shading in Ax6549 due to greater leaf width and having a more horizontal leaf orientation. Morphological data did not help clarify the methods of improved performance of Ax6549 under shaded conditions. Whole canopy photosynthetic measurements performed at different cutting heights are likely needed to further explain the incongruities between photosynthetic and growth analysis data.

Creeping bentgrass (Agrostis stolonifera L.) is a major low-cut cool-season turfgrass used worldwide. The objectives of this research were to: 1) to gain insight into the diurnal fluctuation of N metabolism and effects of cytokinin (CK) and nitrate; 2) to characterize the impacts of N and CK on creeping bentgrass under heat stress; 3) to investigate the simultaneous effects of CK and N on the antioxidant responses of heat stressed creeping bentgrass; and 4) to examine the expression pattern of the major heat shock proteins (HSPs) in creeping bentgrass during different heat stress periods, and then to study the influence of N on the expression pattern of HSPs. The transcript abundance of nitrate reductase (NR), nitrite reductase (NIR), plastidic glutamine synthetase (GS2), ferredoxin-dependent glutamate synthase (Fd-GOGAT), and glutamate dehydrogenase (GDH) and N metabolites in shoots were monitored during the day/night cycle (14/8 h). All the measured parameters exhibited clear diurnal changes, except GS2 expression and total protein. Both NR expression and nitrate content in shoots showed a peak after 8.5 h in dark, indicating a coordinated oscillation. Nitrate nutrition increased diurnal variation of nitrate content compared to control and CKHowever, CK shifted the diurnal in vivo NR activity pattern during this period. Grass grown at high N had better turf quality (TQ), higher Fv/Fm, normalized difference vegetation index (NDVI), and chlorophyll concentration at both 15 d and 28 d of heat stress than at low N, except for TQ at 15 d. Shoot NO3-, NH4+, and amino acids increased due to the high N treatment, but not water soluble proteins. High N also induced maximum shoot nitrate reductase activity (NRmax) at 1 d. CK increased NDVI at 15 d and Fv/Fm at 28 d. In addition, grass under 100 µM CK had greatest NRmax at both 1 d and 28 d. Under high N with 100 µM CK, root tZR and iPA were 160% and 97% higher than under low N without CK, respectively. Higher O2- production, H2O2 concentration, and higher malonydialdehyde (MDA) content in roots were observed in grass grown at high N. The activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), and guaiacol peroxidase (POD) in roots were enhanced by high N at 19, 22, and 24% levels, respectively, relative to low N. Twenty-eight days of heat stress resulted in either the development of new isoforms or enhanced isoform intensities of SOD, APX, and POD in roots compared to the grass responses prior to heat stress. However, no apparent differences were observed among treatments. No CK effects on these antioxidant parameters were found in this experiment. At week seven, grass at medium N had better TQ, NDVI, and Fv/Fm accompanied by lower shoot electrolyte leakage (ShEL) and higher root viability (RV), suggesting better heat resistance. All the investigated HSPs (HSP101, HSP90, HSP70, and sHSPs) were up-regulated by heat stress. Their expression patterns indicated cooperation between different HSPs and that their roles in creeping bentgrass thermotolerance were affected by N level.

Creeping bentgrass (Agrostis stolonifera L.) is commonly used on golf course greens and fairways in cool-humid regions but is plagued by numerous fungal diseases, one of which is dollar spot disease (Sclerotinia homoeocarpa F. T. Bennett). Dollar spot occurs frequently throughout the growing season requiring biweekly fungicide applications for complete control. The objective of this study was to investigate methods of reducing the number of fungicide applications needed to maintain dollar spot at acceptable levels through dew removal and potential mechanisms of resistance in bentgrass. In the first study, a combination of mowing three times a week and dragging by hose the remaining four days to remove dew was used in an attempt to reduce disease severity. The main effect of this combination treatment was not significant (p>0.05) and did not reduce the number of fungicide applications compared to normal mowing three times a week. However, dollar spot was managed curatively with 20-80% fewer applications compared to a normal preventative fungicide program. In the second experiment, two experimental germplasms with varying disease resistance were tested for the possible production of antifungal compounds known as phytoanticipins. Preliminary results indicate the resistant line may contain compounds not present in the susceptible line.

Shade stress on creeping bentgrass (Agrostis stolonifera) causes elongation of leaves, reduced energy availability for growth and lower levels of disease resistance resulting in poor quality putting surfaces. Decreased quantity or photosynthetic photon flux density (PPF) and quality or the red:far red light ratio (R:FR) of light affects the morphology of turfgrass plants by increasing production of giberellic acid and reducing available non-structural carbohydrates. The object of the study was to determine which source of nitrogen (N) is best suited to retaining turfgrass quality in shade and to see if the plant growth regulator trinexapac-ethyl [4-(cyclopropyl-α-hydroxy-methylene)-3,5-dioxo-cyclohexane carboxylic acid ethyl ester] (TE) (Syngenta AG, Switzerland) can improve density and combat the loss of surface quality of bentgrass under tree shade. Field studies were conducted on ‘Penncross’ creeping bentgrass (Agrostis stolonifera) in Columbus, in 2006, and 2007. Under three light environments: full sun (FS), reduced R:FR (DS), and reduced PPF (NS). Light reduction was >90% in both shade areas and the R:FR ratio was .38 in the DS area, 1.28 in NS, and 1.29 in FS. The three N treatments included (NH2)2CO, Ca(NO3)2 and (NH4)2SO4 foliarly applied weekly at a rate of 0.43g m-2 with or without TE applied bi-weekly at 0.3975 L ha-1.Chlorophyll content, along with non-structural carbohydrates, flavonoids, turf canopy color, dry matter and canopy densities were measured. There were no differences in soluble carbohydrate levels between treatments. Chlorophyll levels varied between TE treated and non-treated areas. Applications of (NH2)2CO consistently resulted in higher content of N15 in turfgrass plants also but there was no effect in nitrogen uptake kinetics due to light environment differences. TE had a negative impact on quantities of flavonoids. There was variation between the N treatments in relation to dry matter and carbohydrate content. (NH2)2CO in combination with TE provided the best visual quality surface as the season progressed. TE was effective in reduced PPF conditions and R:FR conditions which would indicate it as a possible product for use in shade management of creeping bentgrass Agrostis stolonifera. It was equally efficient in both light environments suggesting that prior shade research using NS is relevant to shade management in private industry. There was not a strong indication as to a preferred source of N.(NH2)2CO had positive impacts on total chlorophyll content.

Take-all, caused by Gaeumannomyces graminis, is a devastating root disease on cereal crops and turfgrasses worldwide. Three varieties of the fungus have been described and are distinguished from one another based on hyphopodium type and ascospore length. G. graminis var. avenae (Gga) produces simple hyphopodia and generally longer ascospores as compared with G. graminis var. tritici (Ggt) and var. graminis (Ggg). G. graminis isolates were subjected to morphological, molecular and pathogenicity assays in an effort to determine the most reliable method for differentiating varieties. A host pathogenicity test tube assay was developed to induce the formation of perithecia and ascospores and to determine the pathogenicity of isolates on wheat and oats. Gga isolates were distinguished from Ggt and Ggg based on pathogenicity on oats and the production of amplicons with an avenacinase-specific primer set, Gga:AV3. Ggt and Ggg were not distinguished due to overlaps among all characters. Gga is also the causal agent of take-all on creeping bentgrass. A rapid assay was developed and used to determine the effect of root zone mix composition on take-all incidence of creeping bentgrass. Sand type and organic matter amendment were shown to influence disease incidence. Plants grown in mason sands amended with 20% compost (v/v) had significantly less root disease incidence as compared with all other mixes. Gga is the only variety to produce avenacinase, detoxify avenacin and to infect oats. Avenacin production in creeping bentgrass was determined using fluorimetry, TLC and HPLC. Avenacin was not detected in creeping bentgrass and Ggt isolates were shown to be able to infect creeping bentgrass indicating Gga or Ggt may incite take-all patch. The development of a real-time PCR assay for Gga was unsuccessful due non-specific amplification from other varieties. However, avenacinase sequence information obtained indicated Gga and Ggt are more closely related to each other than to Ggg. Although Ggt does not express avenacinase activity, the aspartic acid residues which are believed to be the active sites of the avenacinase enzyme are conserved within the Ggt avenacinase-like gene sequence.