Spring dead spot (SDS), a monocyclic, soil-borne disease caused by Ophiosphaerella spp., affects the rhizomes and stolons of bermudagrass (Cynodon dactylon L. Pers), and is particularly severe in regions with extended dormancy, such as the transition zone. This research evaluates three aspects of SDS management: environmental influences, disease mapping, and the economic feasibility of precision treatments. To measure the relationship between local topography and SDS localization, UAV imagery was collected from 16 golf course fairways across three locations in Virginia and SDS coordinates were recorded. Using state lidar data, environmental factors such as slope, aspect, annual sunlight, and landform type were quantified. Generalized linear mixed-effects models revealed increased odds of SDS occurrence on north-facing slopes and landforms such as peaks and shoulders (p ≤ 0.001), while pits, valleys, and south-facing slopes were associated with decreased odds (p < 0.001). However, topographic features accounted for only 4.2% of the variance in disease distribution, indicating that other factors also play significant roles in SDS development. In parallel, precision treatment strategies (spot and zonal applications) were evaluated in a randomized complete-block design. Compared to full-coverage and untreated controls, precision treatments achieved similar disease control (p ≤ 0.001) while reducing the treated area by 48–52% (p ≤ 0.001), demonstrating a previously described Python script for spring dead spot detections efficacy in generating actionable disease maps. Finally, the economic viability of precision SDS management was assessed at the Independence Golf Club in Midlothian, VA. Cost analyses comparing precision and conventional treatments showed that a GNSS-equipped sprayer, used for precision applications, provided cost savings over a 10-year horizon when applying isofetamid or a combination product of pydiflumetofen + azoxystrobin + propiconazole. Conversely, this strategy was not cost-effective with annual applications of tebuconazole due to its low cost per application. These findings suggest that adopting precision treatment methods with appropriate fungicides can reduce costs and improve sustainability in SDS management. Together, these studies highlight the potential for integrating disease mapping, environmental analysis, and economic modeling to optimize SDS management strategies in turfgrass systems. / Doctor of Philosophy / Spring dead spot (SDS) is the most economically important disease of bermudagrass in the United States. It is caused by Ophiosphaerella spp. of fungi, which infect the horizontal growth structures of the plants causing damage in the fall leaving plants more susceptible to damage over the winter, these areas then fail to emerge from winter dormancy. Damage from SDS is often severe and long lasting making it important to avoid. While SDS has been well-studied, many important questions remain, including ways to improve management efficiency with fungicides and the reasons the disease develops where it does. To address questions on precision management we used a previously described Python script to build custom disease maps of SDS on golf course fairways. We looked at 16 fairways across 3 different locations in Virginia and treated them with either full-coverage applications, precision spot or zonal treatments based on the script, or left them untreated. Fairways treated with the spot and zonal treatments showed similar SDS suppression to full-coverage treatments the following year while using an average of 49% less fungicide. Next, we targeted concerns held by golf course superintendents. The first of these projects looked at the economic viability of these precision treatments over an entire golf course. To answer this, we recorded the amount of labor and money associated with precision treatments over an entire 18-hole course and found that the net present value over 10 years of purchasing a new GNSS sprayer for precision applications could be less than purchasing a new conventional sprayer for traditional applications. Finally, many golf course superintendents will say that SDS occurs more often on north-facing slopes. We looked at SDS locations in fairways that received little to no treatment previously and compared that to topography data. We found that while north-facing slopes and several other factors including the shape of the land itself were more likely to have SDS, the degree to which this is the case is not biologically relevant. These projects together highlight the complex nature of SDS and show that while its biology is complex, it is possible to control using precision turfgrass management techniques.

Nitrogen is an essential plant nutrient in the biosphere. Although N is necessary and beneficial for life, it is also a common pollutant in the atmosphere and hydrosphere as it may be lost to the atmosphere as ammonia (NH3) or nitrous oxide (N2O) gases or to groundwater as nitrate (NO3-) following fertilization. Polymer coated urea (PCU) is one type of N fertilizer which uses temperature-controlled diffusion to control N release to better match plant demand and mitigate environmental losses of N. The objectives of this project were to simultaneously compare the effects of PCU on gaseous (as N2O and NH3) and aqueous (as NO3-) N losses to the environment as compared to uncoated urea in grass systems over the entire PCU N-release period and to investigate the viability of photoacoustic infrared spectroscopy as a method to ascertain N2O and NH3 losses following fertilization. Two field studies were conducted on established turfgrass sites with a mixture of Kentucky bluegrass (KBG; Poa pratensis L.) and perennial ryegrass (PRG; Lolium perenne L.) in sand (Site 1) and loam (Site 2) soils. Each study compared an untreated control to 200 kg N ha-1 applied as either uncoated urea or PCU (Duration 45 CR®). In these studies PCU reduced NH3 emissions by 41-49% and N2O emissions by 16-54%, while improving growth and verdure. Leachate NO3- observations were inconclusive at each site. Glasshouse studies were conducted to compare N2O and NH3 emissions from PCU and uncoated urea to an untreated control utilizing a non-static, non-flow-through chamber in conjunction with photoacoustic infrared spectroscopy (PAIRS) for gas collection and analysis. Three short-term studies (17-21 d) were done with sand, sandy loam, and loam soils and a full-term (45 d) study with the loam soil. Each study was done in maize (Zea mays L.). Volatilization of ammonia was reduced by 72% and 22% in the sandy loam and loam soils, respectively, in 2008-2009 and by 14% in the loam in 2010. Evolution of N2O was reduced by 42% and 63% in the sandy loam and loam soils in 2008-2009 and by 99% in the loam in 2010. Overall, PCU decreased gaseous losses of N following fertilization while providing a steady supply of N to the plant. The utilization of PAIRS is a viable analysis method which gives higher temporal resolution analysis than is typically reported. These considerable decreases in environmental losses of N are major steps toward conserving natural resources and mitigating the negative environmental impacts associated with N fertilization in grass systems.

No description available.

<p dir="ltr">Water scarcity and acute drought continue to be serious concerns, even in humid climates where precipitation normally exceeds evapotranspiration (ET), highlighting the need for improved landscape water conservation practices. Lawns represent the largest area in most managed landscapes and require regular mowing, feeding and sometimes supplemental summer irrigation to persist. A general historical guideline for lawn irrigation is to supply 25-38 mm per growing wk-1 in the absence of rainfall. This fixed volume is often applied on a programmatic “set and forget” three times per week schedule (e.g. M-W-F). This application guideline often results in excess irrigation as it does not take into account plant need or prevailing environmental conditions. Further, in times of acute summer drought policymakers may restrict irrigation to once or twice weekly to conserve water. The effects of these regulations on turf health and potential water savings are unclear. Thus, two multi-year summer field studies were conducted to identify opportunities for improved lawn water conservation. Study one evaluated the effect of varying weekly irrigation volume and frequency on mature Kentucky bluegrass (Poa pratensis L.:KBG) located under a fixed-roof rainout structure. Turfgrass response was measured as visual turf quality (TQ), digital green color (DGC), volumetric soil water content (VWC) and area under the curve for each response variable. In year one, KBG was subject to six irrigation programs and compared to a high deficit control for 49 days. The programs were: 25 mm total water wk-1 applied either three times (M-W-F) or twice (M and F) weekly, 19 mm total wk-1 twice weekly (M and F), 13 mm total wk-1 once weekly and 60 or 80% accumulated ETo three times weekly. Due to poor performance, the high deficit control and 60% ETo were excluded from further evaluation. In year two, seven programs were evaluated: 33 mm total water wk-1 applied once, twice, or three times weekly, or every-other-day, 25 mm total wk-1 applied twice or three times weekly and 80% ETo twice weekly for 63 days. In both years, generally, 25-33 mm wk-1 applied two or three times wk-1 produced the most consistent TQ, DGC and highest VWC. Study two compared three supplemental irrigation programs to a natural rainfall control for six widely planted cool-season lawn grasses for 70 days. The six lawn grasses were: a KBG sod, seeded drought tolerant and susceptible KBG cultivars, a turf-type tall fescue (Schedonorus arundinaceus (Schreb.) Durmort.: TTTF) blend and two KBG and perennial ryegrass (Lolium perenne L.:PRG) mixtures. In Study two, highly significant differences p < .001 occurred for irrigation program and lawn grasses. While supplemental irrigation aided all grasses, rainfall in year one and two measured 119 mm and 343 mm, respectively, affecting data in each study year. Area under the turfgrass quality curve (AUTQC) was lowest for the rainfall control (339 and 425) and highest for 33 mm wk-1 applied three times (507 and 526) and 80% ETo programs (508 and 535) in year one and two, respectively. Annual responses for DGC and VWC generally followed TQ trends. For grasses subject only to natural rainfall, TTTF, and the KBGs were generally superior to the KBG:PRG mixtures, thus emphasizing the importance of species selection. In summary, these studies compared a traditional “set and forget” irrigation program to a range of alternative programs and different lawn grasses. These data provide evidence for irrigation savings by employing a combination of planting drought tolerant lawn species and adopting a more limited irrigation program. Future field studies should include the evaluation of adaptive, data-driven programs based on forecast environmental conditions and threshold responses like DGC or predetermined VWC set points calibrated for varying soil types and growing environments.</p>

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal.

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal

Stormwater runoff has negative impacts on water resources, human health and environment. In this research the effectiveness of Rain Water Harvesting (RWH) systems is examined as a stormwater Best Management Practice (BMP). Time-based, evapotranspiration-based, and soil moisture-based irrigation scheduling methods in conjunction with RWH and a control site without RWH were simulated to determine the effect of RWH as a BMP on a single-family residence scale. The effects of each irrigation scheduling method on minimizing water runoff leaving the plots and potable water input for irrigation were compared. The scenario that reflects urban development was simulated and compared to other RWH-irrigation scheduling systems by a control treatment without a RWH component. Four soil types (sand, sandy loam, loamy sand, silty clay) and four cistern sizes (208L, 416L, 624L, 833L) were evaluated in the urban development scenario. To achieve the purpose of this study; a model was developed to simulate daily water balance for the three treatments. Irrigation volumes and water runoff were compared for four soil types and four cistern sizes. Comparisons between total volumes of water runoff were estimated by utilizing different soil types, while comparisons between total potable water used for irrigation were estimated by utilizing different irrigation scheduling methods. This research showed that both Curve Number method and Mass-Balance method resulted in the greatest volumes of water runoff predicted for Silty Clay soil and the least volumes of water runoff predicted for Sand soil. Moreover, increasing cistern sizes resulted in reducing total water runoff and potable water used for irrigation, although not at a statistically significant level. Control treatment that does not utilize a cistern had the greatest volumes of predicted supplemental water among all soil types utilized, while Soil Moisture-based treatment on average had the least volume of predicted supplemental water.

No description available.