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Doctor of Philosophy / Department of Horticulture, Forestry, and Recreation Resources / Jack Fry and Megan Kennelly / Rough bluegrass (RBG, Poa trivialis L.) is a difficult-to-control weed that commonly infests cool-season turfgrass swards after movement of vegetative propagules or contamination from seed lots. Rough bluegrass is less tolerant of heat stress than desirable cool-season species such as tall fescue (TF, Festuca arundinacea Schreb. Syn [italicize]Schedonorus [italicize]arundinaceus Schreb.), and often declines during mid-summer due to biotic or abiotic stresses. The objectives of these 2011-2013 controlled environment and field experiments were to: 1) observe growth and physiological differences between ‘Laser’ and ‘Pulsar’ RBG and TF; 2) differentiate between physiological and pathological contributors to RBG decline; 3) determine the effects of TF seeding rate and mowing height on TF/RBG establishment when RBG is a seed contaminant; 4) evaluate herbicide combinations for selective RBG control; and 5) evaluate seasonal timing of glyphosate for nonselective RBG control. Tall fescue was less affected by elevated temperature than RBG. At 35°C, Laser and Pulsar experienced similar reductions in quality, gross photosynthesis (Pg), shoot and root biomass, and root length density compared to when grown at 23°C, but maximum electrolyte leakage was greater for Pulsar (63%) than for Laser (49%). Cell membrane thermostability could contribute to the better heat tolerance of Laser RBG. Evaluation of RBG foliage and roots did not reveal a fungal pathogen associated with RBG decline. Still, repeated applications of azoxystrobin (610 g a.i. ha⁻¹) or pyraclostrobin (556 g a.i. ha⁻¹) increased RBG quality, cover, and Pg during summer compared to untreated RBG, possibly due to poorly understood non-target physiological effects of the fungicides. Mowing TF at 7.6 or 11.4 cm reduced RBG incidence up to 57% compared to mowing at 3.8 cm. Tall fescue seeding rate had no effect on RBG incidence. Several herbicides and herbicide combinations resulted in some RBG injury in the field, but bispyribac-sodium was the only treatment that provided RBG control (16 to 92%) in Manhattan, KS; Hutchinson, KS; and Mead, NE. Spring-applied glyphosate resulted in the lowest RBG coverage (1 to 31%) among field studies in Manhattan and Mead, followed by late-summer applications (6 to 58%), and mid-summer applications (9 to 86%).

Bermudagrass (Cynodon spp.) is the most common turfgrass used on golf course putting greens in the southeastern United States (Lyman et al., 2007). In 2013, the National Turfgrass Evaluation Program (NTEP) started a 5-year trial of warm-season putting green cultivars. One of the bermudagrass cultivars in the study is MSB-285 (experimental cultivar). MSB-285 is a sister plant of MSB-264 (Philley and Munshaw, 2011) and is a distinct cultivar of C. dactylon × C. transvaalensis. MSB-285 has a more extensive root system and upright growth habit than traditional bermudagrass putting green cultivars (Philley and Munshaw, 2011). Due to MSB-285’s unique genetic makeup and growth habit, the objectives of this research were to determine if best management practices used to maintain ultradwarf bermudagrasses would be suitable for MSB-285 and to determine the water-use characteristics of MSB-285 compared to industry standard cultivars.

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.