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Water is a basic necessity for turfgrass growth and metabolic processes, with optimal levels required for the maintenance of turf quality and function. As water restrictions for irrigation of landscapes become more widespread across the United States, turfgrass managers will need to rely on management strategies to improve the performance of turfgrasses under reduced irrigation environments. Therefore, the objectives of the research were to (i) compare the performance of different Agrostis species and cultivars under reduced irrigation, (ii) evaluate the use of wetting agents for maintaining turf quality under reduced irrigation, (iii) and examine the physiological mechanisms associated with improved drought resistance traits of Agrostis species. To address our primary objectives, we conducted a two-year field study comparing cultivars of three bentgrass species, including ‘Revere’ and ‘Tiger II’ colonial bentgrasses (Agrostis capillaris), ‘Legendary’ and ‘Greenwich’ velvet bentgrasses (A. canina), and ‘13M’, ‘T-1’, ‘L-93’, and ‘Penncross’ creeping bentgrasses (A. stolonifera) in response to reduced irrigation with and without the use of a wetting agent. In general, the use of a wetting agent did not result in any significant differences in turf quality or soil moisture content among treatments. There were significant differences in turf quality among bentgrass species and cultivars under reduced irrigation. Colonial bentgrass cultivars maintained high turf quality, and were found to be well suited for fairways under reduced irrigation. Due to excessive thatch accumulation in our study, velvet bentgrass cultivars exhibited significant declines in quality regardless of irrigation level. Among creeping bentgrass cultivars, T-1 exhibited improved drought tolerance compared to the older cultivars of creeping bentgrass. Based on results from the field study, we further evaluated the drought resistance and recovery characteristics among five cultivars of colonial bentgrass (‘Barking’, 'Tiger II’, ‘Revere’, ‘Capri’, and ‘Greentime’). Under moderate drought stress, Barking, Tiger II, and Revere all exhibited lower leaf relative water content levels compared to Capri and Greentime, although no significant differences in turf quality or soil water content were observed during the drought period. Following re-watering, Barking and Tiger II exhibited the most rapid recovery from drought (as measured by percent green cover), while Capri and Greentime exhibited delayed recovery. Therefore, although significant differences in turf performance during drought stress were not observed, recovery potential seems to vary among the different cultivars of colonial bentgrass.

Mesotrione is the first triketone herbicide registered for use in turfgrass. Triketones prevent carotenoid biosynthesis by inhibiting the enzyme p-hydroxyphenylpyruvate dioxygenase (HPPD). Although mesotrione controls many species of grass and broadleaf weeds, it is best know for selective control of perennial grasses like creeping bentgrass (Agrostis stolonifera L.). Field trials conducted at Virginia Tech and Blacksburg Country Club determined that several programs that integrate herbicide treatment and turf seeding effectively transitioned creeping bentgrass contaminated golf roughs back to a tall fescue [Schedonorus phoenix (Scop.) Holub] monoculture. However, mature weeds require multiple mesotrione applications for effective control. This requirement is a major limitation to mesotrione's competitiveness in turfgrass markets. Several greenhouse and laboratory studies were conducted to evaluate scenarios where mesotrione rates were titrated and applied daily to mimic ascending, descending, and intervallic time-release patterns. These patterns were applied following an initial treatment to foliage or soil to mimic a potential sprayable or granular time-release formulation. These scenarios effectively controlled five targeted weed species equivalent to the standard of two broadcast sprays, regardless of initial application placement or release pattern. However, both time-release treatments and the standard injured tall fescue based on leaf counts, plant weights, and visual phytotoxicity ratings. Additional growth chamber studies found that changes in relative humidity from 50 to 90% caused a 4- to 18-fold increase in plant phytotoxicity with a concomitant decrease in photochemical efficiency when mesotrione was applied to foliage of smooth crabgrass (Digitaria ischaemum (Schreb.) Schreb. ex Muhl.). Furthermore, white tissue was found predominately in the two youngest leaves when mesotrione was applied to soil, but in older leaves when applied only to foliage. Laboratory studies were conducted to evaluate interspecific differences in 14C mesotrione absorption and translocation between two plant species when applied to foliage or roots. Annual bluegrass (Poa annua L.) absorbed 2- to 4-fold more radioactivity than Kentucky bluegrass (Poa pratensis L.). Both species absorbed less radioactivity through roots than through foliage and root absorbed radioactivity was more often exuded into Hoagland's solution while foliar absorbed radioactivity was often found in other foliage. / Ph. D.

A series of studies were conducted to examine the antioxidant status, drought and disease tolerance, and growth response to foliar application of soluble seaweed (Ascophyllum nodosum) extracts (SE) and humic acid (HA; 25% active HA or 2.9% active HA) in tall fescue (Festuca arundinacea Schreb), Kentucky bluegrass (Poa pratensis L.) and creeping bentgrass (Agrostis palusttis Huds.) grown under low (-0.5 MPa) and high (-0.03 MPa) soil moisture environments. Foliar application of humic acid (2.9 % active HA) at 23.7 and 47.4 l/ha improved leaf water status, shoot and root development in tall fescue, Kentucky bluegrass and creeping bentgrass grown under drought. Humic acid (2.9% active HA) at 15.5 l/ha or SE at 326 g/ha significantly reduced dollarspot incidence and improved turf quality in creeping bentgrass. Drought stress induced an increase of antioxidants alpha-tocopherol and ascorbic acid concentrations in the three turfgrass species. In the experiment with Kentucky bluegrass, drought stress increased beta-carotene concentration, but did not significantly influence superoxide dismutase (SOD) activity. Foliar application of humic acid (25% active HA) at 5 l/ha and/or SE at 326 g/ha consistently enhanced alpha-tocopherol and ascorbic acid concentrations, leaf water status, and growth in the three cool-season turfgrass species grown under low and high soil moisture environments. In the experiment with Kentucky bluegrass, application of HA at 5 l/ha plus SE at 326 g/ha also increased beta-carotene content and SOD activity under low and high soil moisture environments. There were close positive correlations between the antioxidant status and shoot or root growth in the three turfgrass species regardless of soil moisture levels. The antioxidant SOD activity, photosynthetic capacity in terms of Fvm690, and chlorophyll content in terms of Fm730/Fm690 exhibited a seasonal fluctuation in endophyte [Neotiphodium coenophialum (Morgan Jones and Gams) Glenn, Bacon, Price and Hanlin] -free and endophyte-infected tall fescue. Application of SE enhanced SOD activity, photosynthetic capacity, and chlorophyll content in tall fescue, especially at 4 weeks after SE treatment. The SOD activity, photosynthetic capacity and chlorophyll content were not significantly influenced by the endophyte infection. A close positive correlation between SOD and photosynthetic capacity during the summer was found in endophyte-free and endophyte-infected tall fescue. / Ph. D.

Leptosphaerulina spp. are common fungi that have been reported to colonize several turfgrass species. Controversy exists regarding the relationship of Leptosphaerulina spp. and their turfgrass hosts. The fungus has been classified as a saprophyte, senectophyte, weak pathogen, and pathogen of turfgrasses. There has also been conflicting reports regarding the delineation of species within the genus Leptosphaerulina. Because of the uncertainty regarding the ecology and taxonomy of the genus in relation to turfgrasses the present study was undertaken. The ITS and EF-1á gene regions were sequenced and analyzed to compare to the multiple taxonomic schemes reported in the literature. The ITS region offered no resolution of species; however, the phylogeny of the EF-1á gene was consistent with the six-species model of Graham and Luttrell. Inoculation experiments were performed on unstressed and artificially stressed plants to determine whether the fungi are pathogens, senectophytes, or saprophytes of turfgrasses. Perennial ryegrass and creeping bentgrass plants were stressed by placing them in a dew chamber set at 38ºC, 100% R.H., and no light for two and one days respectively. Plants were inoculated with cultures of Leptosphaerulina isolated from turfgrasses, and maintained at optimum conditions reported for infection and colonization. There was no visible difference between inoculated and uninoculated plants, and examination of cleared and stained leaves with a light microscope revealed spores that germinated and produced appressoria, but failed to penetrate the epidermal cells. The lack of infection and colonization suggests that Leptosphaerulina spp. are saprophytes of turfgrasses. / Master of Science

Urban development alters the physical and chemical properties of soil which presents challenges for vegetation establishment. Compost, when applied as a soil amendment, can help to ameliorate these challenges. In field trials, we evaluated the effect of surface-applied composts and standard hydroseeding applications on changes in soil properties and turfgrass stand on a highway roadside. The short-term effects of (1) no compost application; (2) 2.5 cm compost surface mulch; (3) 2.5 cm compost application, incorporated; (4) 5.0 cm compost application, incorporated; (5) 0.6 cm compost blanket; and (6) straw mat on turfgrass establishment, quality and changes in soil properties were measured on an urban soil devoid of topsoil. In greenhouse studies, we compared the effect of depth of planting of two variously-sized turfgrass seeds in compost. The soils of the disturbed roadside and the urban soil had increased Mehlich I-extractable soil K, Mg, and P following compost application. Analysis of botanical composition on the highway roadside demonstrated that the percentage of fescue decreased with time, while weed species increased inversely in both treatments. Compost amendments on the urban soil increased turfgrass color over time, whereas turfgrass density was not affected by time. Turfgrass density was greatest in applications of a 5 cm depth compost incorporated 7-10 cm into the soil. No differences were observed in biomass harvested among treatments. Tall fescue seeds had greater germination and establishment than smaller sized bermudagrass seeds when sown below the surface of compost, regardless of depth. Composts help to regenerate topsoil-like functionality in disturbed soils by promoting vegetation establishment, including weeds, on highway roadsides and improving turf quality on urban soils. / Master of Science

Dollar spot is one of the most common diseases of warm- and cool-season turfgrass stands and is especially devastating on creeping bentgrass (Agrostis stolonifera L.). The fungus Sclerotinia homoeocarpa degrades the foliage by creating silver, dollar-sized depressions of dead and bleached turf. Frequent fungicide applications and cultural management strategies are required throughout the growing season to prevent or reduce severity of this disease. Previous research has demonstrated that ferrous sulfate applied at 48.8 kg ha-1 suppresses dollar spot epidemics without traditional fungicides. In vitro studies showed 100 to 1,000 mg kg-1 of ferrous sulfate directly suppressed S. homoeocarpa growth of an isolate collected from an established, intensively-maintained creeping bentgrass putting green. Genetic diversity of S. homoeocarpa segregates isolates into two groups; strains generally associated with warm-season and cool-season grasses. It is unknown whether isolates of each group react similarly in the presence of ferrous sulfate. Our research explored use rates of ferrous sulfate required to suppress 50% of dollar spot in the field and in vitro. Ferrous sulfate (heptahydrate 20% Fe, Valudor Products Inc) rates in field trials included 0, 4.88, 24.4, 48.8, and 97.6 kg ha-1. Our results indicate a hyperbolic relationship between ferrous sulfate rate and dollar spot reduction. Using this model, 26.4 kg ha-1 reduced dollar spot incidence by 50%. We concluded that ferrous sulfate suppresses 50% of S. homoeocarpa mycelial growth at between 480 and 720 mg L-1 concentration in 0.25 strength potato dextrose agar in vitro, and fungitoxic activity of ferrous sulfate was dependent primarily on historical fungicide inputs at isolate collection sites. The use of ferrous sulfate may supplement traditional fungicide use. Chlorothalonil is the most common fungicide used to suppress dollar spot in turfgrass. Annual site-use limitations of chlorothalonil often prevent turf managers from achieving acceptable dollar spot control throughout the season. It is not known how ferrous sulfate may contribute to a successful chlorothalonil fungicide program. Therefore, we examined whether ferrous sulfate can be used to minimize chlorothalonil requirements through reducing active ingredient concentrations and extending the longevity, while still maintaining acceptable disease control. Chlorothalonil treatments were applied at 0, 2.28, 4.57, 6.86, and 9.16 kg ai ha-1 (Daconil WeatherStik) across plots treated with and without 48.8 kg ha-1 ferrous sulfate applied bi-weekly. Ferrous sulfate reduced the chlorothalonil rates necessary for 80% disease reduction by 36 to 51% across all trials. Additional studies showed that ferrous sulfate applied with chlorothalonil increased duration of disease control by five days and eliminated two seasonal treatments. Our research expands the guidelines for practical ferrous sulfate usage for dollar spot suppression by elucidating the rate-to-disease relationship and providing best management practices involving admixtures with chlorothalonil. / Master of Science / Turfgrass systems offer many environmental and recreational benefits. Managing turfgrass stands that are free of damaging turf pests is essential to providing aesthetically pleasing lawns, golf courses, and sports fields. Creeping bentgrass is one of the most common turfgrass types found on golf course putting greens but is also used on golf course fairways and tee boxes. There are many diseases that can be found on creeping bentgrass when environmental conditions are favorable. Of these diseases, dollar spot is the most common. When dollar spot is present, half-dollar sized spots of bleached turf can be seen. In order to prevent these easily noticeable spots from appearing, fungicide applications are required in a given growing season to prevent the pathogen from infecting. Available fungicides are very effective at providing control but can be very costly. Beyond fungicide use, other research has shown various cultural practices to reduce disease incidence. Previous research has shown that iron sulfate applied to creeping bentgrass can reduce dollar spot epidemics without the use of fungicides. Laboratory studies have shown a similar trend as ferrous sulfate at varying concentrations directly suppressed dollar spot pathogen growth. In both cases, a limited range of ferrous sulfate rates was tested. To obtain more information we explored use rates of ferrous sulfate required to suppress 50% of dollar spot in the field and in vitro. Ferrous sulfate rates in field trials ranged from 0 to 97.6 kg ha⁻¹ . Results from these trials were used to create a hyperbolic regression. Using this model, we were then able to determine that 26.4 kg ha⁻¹ iron sulfate was required to suppress 50% of the dollar spot in the field. For the laboratory studies we concluded that ferrous sulfate suppresses 50% of the dollar spot pathogen mycelial growth between 480 and 720 mg L ⁻¹ iron sulfate concentrated potato dextrose agar. Although there are many different fungicides available for dollar spot control, the active ingredient chlorothalonil is the most common used. Due to the mode of action which chlorothalonil exhibits, it is much less likely that the pathogen causing dollar spot can become resistant. Although resistance is not an issue, governmental annual site-use limitations restrict turf managers from achieving desirable control. The use of iron sulfate in conjunction with chlorothalonil has not been previously studied. Chlorothalonil treatments were applied at a range of labeled use rates across plots treated with and without 48.8 kg ha⁻¹ ferrous sulfate applied bi-weekly. Ferrous sulfate reduced the chlorothalonil rates necessary for disease reduction. If a threshold of 80% is used, up to 50% reduction in chlorothalonil use was observed. Supplemental studies investigating the duration of control achieved by the combination showed an increase of up to 5 days and eliminated the need for two applications across one season. This research fills a huge gap in our knowledge base on the practical use of iron sulfate for dollar spot control.

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Ryegrass cultivars, experimental accessions, blends and composite mixtures were tested for overall adaptation to overseeded turfgrass management practices under desert conditions. Entries were significantly different from each other for color and overall turfgrass quality. Gennplasm for overseeding differs for tolerance to close mowing under desert conditions. In most cases, the better adapted entries had superior scores in two years of testing.

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