Low temperature injury is among the greatest challenges facing golf courses with ultradwarf bermudagrass (UDB) (Cynodon dactylon (L.) Pers. x C. transvaalensis Burtt-Davy) putting greens in Virginia. This research focused on the impact of turf covers, fungicide programming, core aeration, and trinexapac-ethyl (TE) on UDB cold tolerance, winter quality, and cold de-acclimation (CD). Our results indicate that the use of turf covers significantly increased UDB canopy and soil temperatures when air temperatures were below -3.9°C. Air gaps under covers and the use of double turf covers increased soil and canopy temperatures compared to single covers alone in some instances, but results were inconsistent. Late fall and early winter fungicide applications of chlorothalonil and azoxystrobin improved UDB quality throughout winter dormancy and spring green up. The addition of a pigmented phosphonate significantly improved winter and spring UDB quality. The addition of acibenzolar-S-methyl to fungicide programs did not improve winter UDB quality or spring green up. Summer core aeration programs were evaluated for their impact on spring green up, turfgrass quality, surface firmness, and moisture retention. Spring UDB green up was improved incrementally as surface disruption increased. Treatments with 20%, 15%, and 10% surface disruption produced higher color vs treatments with lower surface disruption. Surface firmness and volumetric water content of UDB were impacted by construction method but were not significantly impacted by core aeration programs. Field research revealed that 'fall only' and 'fall and winter' TE applications improved UDB quality but only 'fall and winter' delayed UDB premature CD in early spring when UDB can be susceptible to low temperature injury. Growth chamber studies evaluated the impact of TE on UDB cold tolerance to -9.4°C x time duration. Regression analysis predicted a 50% mortality exposure point for UDB under TE treatments of 9.84 hours at -9.4°C (r2=0.836) compared to 11.38 hours at -9.4°C (r2=0.671) for non-treated UDB during cold acclimation. Winter and spring scenarios resulted in delayed CD under TE but no differences in cold tolerance when exposed to -9.4°C. Together, these results increase our understanding of the impact of management practices on UDB winter quality, CD, and low temperature injury. / Doctor of Philosophy / Ultradwarf bermudagrass putting greens are commonly found on golf courses in warm climates. These grasses thrive in heat and humidity but are susceptible to injury or death when exposed to cold temperatures. This research is focused on evaluating management practices that may impact bermudagrass' susceptibility to injury from cold temperature exposure. The cultural practices evaluated include turf covers, fungicide programming, core aeration, and the use of plant growth regulators to manipulate the turfgrasses own self defense mechanisms. Our results show that the use of turf covers significantly increased putting green canopy and soil temperatures when air temperatures were below -3.9°C. Air gaps under covers and the use of double turf covers increased soil and canopy temperatures compared to single covers alone in some instances, but results were inconsistent. Late fall and early winter fungicide applications of commonly-used fungicides improved putting green quality throughout winter dormancy and spring green up. The addition of a green-pigmented phosphonate fungicide significantly improved winter and spring putting green quality. The addition of a plant defense activator, acibenzolar-S-methyl to fungicide programs did not improve winter quality or spring green up. Summer core aeration programs were evaluated for their impact on spring green up, turfgrass quality, surface firmness, and moisture retention. Spring green up was improved incrementally as surface disruption increased. Treatments with 20%, 15%, and 10% surface disruption produced higher color vs treatments with lower surface disruption. Surface firmness and soil moisture content of the putting greens were impacted by construction method but were not significantly impacted by core aeration programs. Field research revealed that 'fall only' and 'fall and winter' plant growth regulator applications improved ultradwarf bermudagrass quality but only 'fall and winter' delayed premature green-up in early spring when the turfgrass can be susceptible to low temperature injury. Growth chamber studies revealed that plants treated with the growth regulator, trinexapac-ethyl were more sensitive to low-temperature exposure than non-treated plants. Together, these results increase our understanding of the impact of management practices on UDB winter quality, CD, and low temperature injury.

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. / Doctor of Philosophy / Goosegrass and smooth crabgrass 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. Although potentially injurious, topramezone (Pylex™) can control these weeds, especially goosegrass, at low doses. Low-dose Pylex™ may also improve bermudagrass and creeping bentgrass response. An initial investigation evaluating tembotrione (Laudis®), Pylex™, and mesotrione (Tenacity®) in different turfgrass species showed that Kentucky bluegrass, perennial ryegrass, and tall fescue were highly tolerant to Pylex™ at rates ranging from 0.75 to 2.25 fl. oz./A, while creeping bentgrass and bermudagrass were low to moderately tolerant to Pylex™. Further investigation suggested that frequent, low-dose (less than 0.25 fl. oz./A) Pylex™ applications or metribuzin (Sencor®) admixtures could enhance weed control and may conserve turfgrass quality. A novel mixture of Pylex™ at 0.15 fl. oz./A and Sencor® at 4 oz. wt./A controlled goosegrass effectively and reduced bermudagrass injury to near acceptable levels and significantly less than Pylex™ applied alone at 0.25 fl. oz/A. In an attempt to further enhance bermudagrass tolerance to Pylex™, post-treatment irrigation was applied at different timings. When bermudagrass turf was irrigated at 15 or 30 minutes after herbicide treatment, bermudagrass injury was reduced to acceptable levels when following Pylex™ at 0.25 fl. oz./A plus Sencor® at 4 oz but not when following Pylex™ applied alone at 0.5 fl. oz./A. Goosegrass control was reduced significantly by post-treatment irrigation in all cases, while irrigation reduced goosegrass control by low-dose Pylex™ plus Sencor® to below-commercially-acceptable levels. Novel, low-dose, frequent application programs containing Pylex™ or siduron (Tupersan®) were developed for season-long crabgrass or goosegrass control in creeping bentgrass greens. Greens-height creeping bentgrass quality was preserved following five biweekly treatments of Tupersan® at rates between 6 and 24 lb./A and Pylex™ at 0.125 fl. oz./A. Tupersan® programs controlled smooth crabgrass and suppressed goosegrass while Pylex™ programs controlled goosegrass and suppressed smooth crabgrass. The data from these studies indicate that utilizing low-dose Pylex™ in combination with Sencor® can impart acceptable bermudagrass safety while also controlling goosegrass effectively. For creeping bentgrass greens, the low-dose, frequent application of Tupersan® is the safest legal option for golf course superintendents to control smooth crabgrass effectively, while having some ability to suppress goosegrass.

Field studies were conducted during 2006 and 2007 to evaluate control of saw greenbriar and southern dewberry by various pasture herbicides and to assess forage tolerance of Tifton 85 bermudagrass to these herbicides. Herbicides evaluated in each study included triclopyr, picloram, 2,4-D, fluroxypyr, dicamba, aminopyralid, metsulfuron methyl and various combinations of the above. Visual ratings were taken on each herbicide efficacy experiment. Visual evaluations of phytotoxicity, measurements of dry matter yield, and forage quality were quantified for each of the bermudagrass tolerance trials. Saw greenbriar was best controlled at approximately one year after treatment by triclopyr at 10.9% ae v/v with diesel as the carrier (88-98%), although the lower rate of triclopyr + diesel at 0.87% ae v/v + 5% v/v and triclopyr alone at 0.87% ae v/v provided 49 to 86% control. Triclopyr + fluroxypyr at 0.25% ai v/v + 0.086% ai v/v gave best control of southern dewberry in both years when applied as an individual plant treatment (IPT) six weeks after shredding. In general, shredding 45 days prior to herbicide application gave an advantage to southern dewberry control versus not shredding. In 2006, triclopyr + fluroxypyr (IPT) was the only treatment to decrease Tifton 85 dry matter yield at the first harvest, with no effect observed at the second harvest. In 2007, both broadcast treatments containing triclopyr + fluroxypyr and the IPT treatment of triclopyr decreased dry matter yield at the first harvest, with triclopyr (IPT) being the only treatment to lower dry matter yield at the second harvest. Field studies were also conducted in 2006 and 2007 to assess sharppod morningglory control in Roundup Ready Flex® and LibertyLink® cotton systems. Herbicides evaluated included glyphosate, glufosinate, prometryn, fluometuron, and diuron. Visual ratings of percent weed control and sharppod morningglory plant counts were taken to assess control. Prometryn at 1.8 kg ai ha⁻¹ and fluometuron at 1.8 kg ai ha⁻¹ provided significant preemergence control (33-81%) of seedling sharppod morningglory. All rates of glyphosate (1.06 and 1.54 kg ai ha⁻¹) and glufosinate (0.45 and 0.6 kg ai ha⁻¹) controlled sharppod morningglory from 55 to 100% at both application timings. The addition of diuron at 1.12 kg ai ha⁻¹ to glyphosate and glufosinate at the late season application enhanced sharppod morningglory control by 3 to 16%. Additionally, in both years, no reduction in cotton yield was observed in the morningglory infested treatment when compared to the weed free treatment.

As average global temperatures rise, cool-season C3 turfgrasses, such as the most commonly grown Kentucky bluegrass (Poa pratensis L.; KBG), struggle to tolerate extreme summer heat and increase their water consumption. Hybrid Bermudagrass (Cynodon dactylon [L.] Pers. × Cynodon transvaalensis Burtt Davy; HBG) is a warm-season C4 grass that may be increasingly suited for northern ecosystems traditionally classified as transition or cool-season climate zones. Glasshouse and field studies were conducted to compare HBG and KBG water use. The objective of the glasshouse study was to evaluate plant health and growth for two HBG cultivars (‘DT-1’ and ‘NorthBridge’) compared to a blend of KBG cultivars in all combinations of deficit, moderate, and high irrigation at optimum or short mowing height. The study was conducted in a glasshouse at Provo, UT, USA from 2020-2021. Grass was grown in pots arranged in a randomized complete block, full factorial design, with four replications of each treatment. The moderate KBG was also significantly different from both high and deficit for verdure and for the last half of NDVI. The objective of the field study was to evaluate two HBG cultivars (‘Tahoma 31’ and ‘Latitude 36’) compared to a blend of KBG cultivars for water loss and canopy health, temperature, and growth when subjected to deficit, moderate, and high irrigation. The study was arranged in a randomized complete block, full factorial design with three replications per treatment, and was conducted at Provo, UT, USA throughout the summer of 2021. In both the glasshouse and field trials, the deficit irrigated KBG consistently scored lower for NDVI and visual turf quality than all other treatments, including moderate and high KBG. This same trend was seen in the field study for percent cover. Although not observed in the glasshouse trial, it was observed in the field trial that the different irrigation levels of HBG resulted in no significant differences for any measurements but the HBG regularly scored better than KBG. The canopy temperatures of deficit irrigated KBG were also higher than all other treatments on most dates. The shoot mass, thatch mass, and total biomass of KBG were significantly less than either HBG cultivar. In the glasshouse trial it was observed that all deficit grasses were significantly lower than the other irrigation treatments and HBG had significantly deeper roots than KBG, although these results were not seen in the field trial. The data suggest that irrigation needs will be less for HBG than KBG and that HBG could provide a water-saving turfgrass alternative to KBG in semi-arid, cool-season regions with increasing water scarcity.