Master of Science / Department of Horticulture, Forestry, and Recreation Resources / Jack D. Fry / Dollar spot, caused by Sclerotinia homoeocarpa F.T. Bennett, and silvery-thread moss (Bryum argenteum Hedw.) are pests affecting creeping bentgrass (Agrostis stolonifera L.) that typically require pesticide inputs. New strategies for pest management may reduce chemical inputs. The objectives of these 2009-2010 field studies were to evaluate: 1) creeping bentgrass cultivars for dollar spot susceptibility; 2) alternative chemical controls for silvery-thread moss; and 3) the response of silvery-thread moss to nitrogen (N) sources. During peak dollar spot development, ‘Declaration’, ‘A-4’, and ‘Crenshaw’ had 7.5, 139.4, and 288.9 infection centers m[superscript]-2 under fairway and 2.1, 27.2, and 106.9 infection centers m[superscript]-2 under putting green conditions, respectively. Two spring and two fall spot applications of sodium or potassium bicarbonate (45 g a.i. L[superscript]-1), premixed essential oil, and broadcast applications of carfentrazone-ethyl at 0.09 kg a.i. ha[superscript]-1 suppressed moss 39% to 55% compared to untreated in 2009. Spot sprays of sodium or potassium bicarbonate, and essential oil, were phytotoxic to creeping bentgrass and required up to 8 or 18 days, respectively, to return to acceptable quality. Fertilization with liquid urea (N at 16.3 kg ha[superscript]-1 biweekly, 210 kg ha[superscript]-1 annually) resulted in 147%, 150%, and 155% more moss than fertilization with IBDU, organic N, and granular urea, respectively, and 156% more moss compared to untreated. Fertilization with urea (liquid or granular) resulted in the best creeping bentgrass color. Averaged across the entire season, plots treated with organic N had unacceptable color in 2009. Nitrogen concentrations in moss tissue ranged from 0.4% to 1.0% and were always significantly lower than N concentrations observed in creeping bentgrass (1.1% to 2.1%), regardless of treatment. In 2010, moss treated with liquid urea had higher tissue N concentrations (1.0%) than untreated moss (0.5%) or that fertilized with IBDU (0.4%). In summary, use of dollar spot-resistant creeping bentgrass cultivars could reduce fungicide requirements. Bicarbonate and essential oil products can reduce moss severity at a similar level to carfentrazone-ethyl, but rates and/or application methods need to be optimized to avoid injury to creeping bentgrass. Applications of liquid urea enhanced moss coverage in creeping bentgrass compared to other N sources.

Master of Science / Department of Horticulture and Natural Resources / Dale J. Bremer / Recent advances in small unmanned aerial systems (sUAS) may provide rapid and accurate methods for turf research and management. The study was to evaluate early drought detection ability of ultra-high resolution remote sensing with sUAS technology, and compare it with traditional techniques on fairway-height ‘Declaration’ creeping bentgrass (Agrostis stolonifera L.) treated from severe deficit to well-watered irrigation (15, 30, 50, 65, 80, and 100% evapotranspiration replacement). Airborne measurements with a modified digital camera mounted on a hexacopter included reflectance from broad bands (near infrared [NIR, 680-780 nm], and green and blue bands [overlapped, 400-580 nm]), from which eight vegetation indices (VIs) were derived for evaluation. Canopy temperature was measured only in the final year with a thermal infrared camera mounted on a drone. Traditional measurements were volumetric water content (VWC), visual quality (VQ), percentage green cover (PGC), and VIs from handheld devices. Declines in VWC in irrigation-deficit treatments were consistently detected by the NIR band and six VIs from sUAS, and NDVI and red band from a handheld device, before drought stress was evident in VQ. These bands and indices predicted drought stress at least one week before symptoms appeared in VQ. Canopy temperature predicted drought stress as early as the best VIs and NIR, 16 days before symptoms appeared in VQ in 2017. Only the NIR and GreenBlue VI [(green-blue)/(green+blue)] consistently predicted drought stress throughout three years. Results indicate using ultra-high resolution remote sensing with sUAS can detect drought stress before it is visible to the human eye and may prove viable for irrigation management on turfgrass.

Managing soil hydrophobicity caused by localized dry spots (LDS) on sand based golf greens has become one of the greatest challenges for golf course superintendents and managers, especially as water restrictions intensify. The purpose of this study was to evaluate the effectiveness of thirteen soil surfactants in eliminating LDS and in maximizing root zone soil moisture on a sand based USGA golf green located on the California Central Coast. Potential water repellency of air dried cores (measured utilizing the water droplet penetration time (WDPT) method), phytotoxicity, and climate were analyzed during two experimental trials. Phytotoxicity data was collected for Trial I using visual quality ratings and for Trial II using a chlorophyll meter. Phytotoxicity decreased during Trial I. Differences in phytotoxicity as measured using chlorophyll index were not at all significant during Trial II (p = 1). Ten of the thirteen wetting agent treatments significantly (p < 0.001) decreased soil hydrophobicity compared with the other wetting agent treated plots and the non-treated control. More frequent application of Cascade Plus resulted in a more significant reduction in soil hydrophobicity. Increasing the application rates also resulted in the reduction of soil hydrophobicity. Wetting agent treatment 6-CP(10day) maintained the highest volumetric water content (VWC) but treatment 13-2079337 maintained the highest levels for wetting agents treated monthly.

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.

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. / Master of Science

A series of studies were initiated to investigate growth responses of Kentucky bluegrass (Poa praetensis L.) and creeping bentgrass (Agrostis palustris Huds.) to foliar applications of two plant growth regulators (PGR) and/or chelated Fe (Na Fe diethylene triamine pentaacetate). Environmental variables considered were N levels, soil moisture regimes, and saline irrigations. The two materials investigated for PGR properties were a commercial product called Roots (a cold-water extract of seaweed and peat humus fortified with "intermediate metabolites" and thiamine) and the systemic fungicide propiconazole, trade name: (Banner) and chemical name: [1- {(2-(2,4-dichlorophenyl)-4-propyl-l,3-dioxolan-2yl}methyl-l H-1,2,4-triazole]. Fortified seaweed extract (FSE) was applied at 9.3 L/ha, and propiconazole (PPC) was applied at 0.93 L a.i/ha. Each was applied alone or in conjunction with chelated Fe at 0.11 kg a.i/ha. Kentucky bluegrass foliage height, root and shoot dry weight, and several foliar nutrients increased following PGR treatments when grown under either limited soil moisture or saline irrigation. Foliar applications of PGR and/or chelated Fe to creeping bentgrass reduced wilting and evapotranspiration, and increased leaf water status, root strength, and shoot dry matter at two levels of N during and after drought stress. / Ph. D.

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. / Doctor of Philosophy / Annual grasses are difficult to control in "high-end" golf turf because few herbicides can be safely used near greens and key weeds have become resistant to the most common products. Several new products were tested for safety on hybrid bermudagrass greens. Methiozolin (PoaCure) was safe for use after post-dormancy greenup, endothall was safe when used while turf was still dormant, and cumyluron was safe regardless of application timing. The duration of preemergence weed control with methiozolin is reduced as temperatures increase and in turfgrass compared to bare ground systems. Half of the methiozolin product will dissipate in 14 days or less when applied to hybrid bermudagrass putting greens or Kentucky bluegrass lawns in spring. Methiozolin controlled smooth crabgrass for the entire season in several Southeastern states, but goosegrass control was slightly below acceptable levels when the product was used within annual dose restrictions. Applicators, such as dabbers and spot sprayers, that are used to treat individual plants improve turf safety and reduce chemical cost, but these devices had not been previously tested for uniformity of fluid output. Studies found that these devices can vary in output by several orders of magnitude depending on the type of devices used, the person using the device, and duration of contact with the turf as the user presses a dabbing device over a weed. Within-device errors were equally problematic and governed by the amount of downward pressure exerted by the fluid contained in the device reservoir. For every 10% of fluid capacity added, fluid dispense rate increases approximately 33%. When the air seal of the fluid fill cap is broken, fluid output approximately doubles compared to when this seal is maintained because loss of vacuum increases downward force of the fluid column. These studies suggest that new products are available to improve annual grassy weed control in ornamental turf, but proper application timing and device calibration is important to achieve best results.

No description available.

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. / Ph. D.

No description available.