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Annual bluegrass is a winter annual grass that is problematic on golf putting greens due to its light green color, prolific seedhead production and intolerance to stress. On creeping bentgrass putting greens, herbicides for annual bluegrass control are limited. A new herbicide, methiozolin, developed by Moghu Research Center, LLC, in Daejeon, South Korea, safely and selectively controls annual bluegrass in creeping bentgrass and several other turfgrass species. Methiozolin typically controls annual bluegrass over several weeks, allowing desirable turfgrass time to grow into areas previously infested by annual bluegrass with little surface disruption. The mode of action of methiozolin is unknown, but has been proposed to act as either a cell wall biosynthesis inhibitor (CBI) or an inhibitor of tyrosine aminotransferase (TAT). Field studies were conducted at Virginia Tech to investigate strategies promoting surface recovery on putting greens following atypically rapid annual bluegrass loss resulting from methiozolin application, intensive core-cultivation as well as potential interactions with plant growth regulators (PGR's), like ethephon. In the rapid annual bluegrass removal study, all treatments receiving additional fertility via synthetic fertilizer with or without trinexapac-ethyl or biostimulant recovered 1 to 3 weeks more quickly than treatments that did not include additional fertility. Addition of the PGR trinexapac-ethyl inconsistently regulated speed of canopy recovery, both increasing and decreasing recovery speed. Under normal maintenance conditions, methiozolin does not negatively influence putting green recovery, however, if the putting green is exposed to droughty conditions, methiozolin can reduce recovery time by several weeks. Core-cultivation should be avoided in conjunction with methiozolin and ethephon applications because when this procedure was conducted on the same day as herbicide application it significantly damaged creeping bentgrass, reducing cover to 19% at 2000 g ai ha⁻¹, compared to the non-treated at 62%. Regarding the question of methiozoling mode of action, laboratory studies supported the claim that addition of exogenous 4-hydroxyphenylpyruvate (4-HPP) alleviates symptoms of methiozolin exposure in lesser duckweed, a model monocot species, but feeding various turfgrass species and annual bluegrass exogenous 4-HPP did not alleviate symptoms. Creeping bentgrass secondary root length and density was not affected by methiozolin, although annual bluegrass, Kentucky bluegrass and perennial ryegrass secondary root lengths were reduced. Based on these data, it does not appear that TAT inhibition is a primary mode of action of methiozolin in turfgrass. Studies were conducted to determine if methiozolin inhibited cell wall biosynthesis in desirable turfgrass species and annual bluegrass. All species exhibited decreased enrichment of ¹³C in cell-wall sugars form ¹³C-glucose in response to methiozolin and a known cell wall biosynthesis inhibitor, indaziflam. Indaziflam and methiozolin at 0.01 µM inhibited ¹³C enrichment of all sugars less than methiozolin at 1.0 µM, for xylose, arabinose and glucose, but not galactose. Addition of 4-HPP increased incorporation of ¹³C into xylose, but had no other influence on ¹³C incorporation into other cell wall sugars. Lack of species specific response indicates that cell wall biosynthesis inhibition is probably not the source of interspecific species responses observed in the field. / 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.

Annual bluegrass (Poa annua L.) and roughstalk bluegrass (Poa trivialis L.) are among the most troublesome grass weeds on golf courses throughout the United States. Herbicides for selective control of these weeds in cool-season fairways are limited and ineffective. Methiozolin is a new isoxazoline herbicide that controls annual bluegrass on putting greens and shows promise for possible weed control in fairways. Kentucky bluegrass (Poa pratensis L.) is among the most common turfgrass species used for golf fairways in the Northern United States and its response to methiozolin has scarcely been tested. A 2.5-yr field study was conducted at four Virginia locations to evaluate methiozolin efficacy for selective annual bluegrass and roughstalk bluegrass control in creeping bentgrass (Agrostis stolonifera L.) or Kentucky bluegrass fairways. Another study evaluated the response of 110 Kentucky bluegrass varieties to three rates of methiozolin. Annual bluegrass has long been presumed to impact putting green trueness, or the ability of the greens canopy to provide a smooth and directionally-consistent ball roll. Although much research has evaluated the impact of greens management on ball roll distance, no peer-reviewed research has evaluated how canopy surface factors, such as weedy annual bluegrass, will influence ball roll direction. Laboratory and field research was conducted to elucidate and overcome experimental errors that may be limiting assessment of ball directional imprecision caused by greens canopy anomalies. Techniques to minimize experimental error were employed in field studies at two Virginia golf courses to determine the influence of annual bluegrass on ball directional imprecision, bounce, and acceleration. Study results suggest that annual bluegrass patches in a creeping bentgrass putting surface can cause subtle increases in ball directional imprecision and bounce but several sources of error must be controlled before these effects can be measured. By using a mechanical putter to avoid directional errors associated with simulated-putt devices, selecting golf balls with balanced centers of gravity, eliminating legacy or "tracking" effects of repeated ball rolls via canopy brushing, and scoring ball direction 30 cm prior to terminal acceleration, we were able to detect an increase in ball directional imprecision of 8 mm m⁻¹ when balls rolled over a single patch of annual bluegrass compared to adjacent rolls on visually-pure creeping bentgrass. In herbicide efficacy studies, methiozolin-only treatments did not significantly injure creeping bentgrass or Kentucky bluegrass, reduce quality, or reduce normalized difference vegetative index regardless of application timings and rates. In general, fall applications of methiozolin reduced roughstalk bluegrass and annual bluegrass cover more than the spring-only treatments. At 1 year after the last treatment, methiozolin at 1500 g ha⁻¹ applied four times in fall at 2-wk intervals for two consecutive years controlled roughstalk bluegrass and annual bluegrass ≥85% and more consistently than other herbicides or treatment regimes. Spanning 110 Kentucky bluegrass varieties, a commercially-acceptable threshold of 30% Kentucky bluegrass injury required between 3.4 to more than 10 times the methiozolin rate needed for annual bluegrass control. Results indicate that annual bluegrass increases directional imprecision and bounce of golf balls rolling across a greens canopy. Methiozolin could be a viable herbicide for managing annual and roughstalk bluegrass in Kentucky bluegrass and creeping bentgrass fairways but weed control efficacy may be dependent on application timing. By measuring small differences in ball directional imprecision as influenced by greens canopy factors, future research efforts will aim to help turf managers choose appropriate greens management techniques. / Ph. D.