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. / Annual bluegrass and roughstalk bluegrass are among the most troublesome grass weeds on golf courses throughout the United States. Both these weedy bluegrass species reduces the aesthetics and playability of golf turf, including fairways, tees, and putting greens. Since both annual bluegrass and roughstalk bluegrass favors growing conditions very similar to that of desirable cool-season grasses, especially Kentucky bluegrass and creeping bentgrass – the most prominent cool-season grasses on golf courses throughout the Northern USA, selective removal of these weedy bluegrass species from the desirable turf sward is very difficult. Moreover, genetic similarity of annual bluegrass and roughstalk bluegrass to Kentucky bluegrass accentuates the difficulty in selective control even more. Commercially-available herbicides for selective control of these weedy bluegrass species in cool-season golf fairways are limited and often ineffective for long-term control. Methiozolin (PoaCure®) is a new herbicide that has been extensively studied and shown to control annual bluegrass on golf putting greens and shows promise for possible weed control in fairways. However, PoaCure® has scarcely been tested to selectively and safely control annual bluegrass and roughstalk bluegrass in cool-season golf fairways. Therefore, field research was conducted at four Virginia locations to evaluate PoaCure® efficacy for selective, long-term annual bluegrass and roughstalk bluegrass control in creeping bentgrass or Kentucky bluegrass fairways. To assess the weed-control potential of PoaCure® on a broader spectrum of Kentucky bluegrass varieties grown here in VA and other cool-season grass growing parts of the nation, another field research was conducted to evaluate the response of 110 Kentucky bluegrass varieties to three different field application rates of PoaCure®. In PoaCure® weed control efficacy studies, PoaCure® by itself did not injure or reduced quality of creeping bentgrass or Kentucky bluegrass regardless of application timings and rates. In general, fall applications of PoaCure® reduced roughstalk bluegrass and annual bluegrass green cover more than the spring-only treatments. At trial completion, which was 2.5 years after trial initiation and 1 year after the last herbicidal treatment, PoaCure® at 82 fl oz/A applied four times in fall at 2-wk intervals for two consecutive years provided ≥85% control of annual bluegrass and roughstalk bluegrass and did so more consistently than other herbicides or treatment regimes in the study. In the tolerance study of 110 Kentucky bluegrass varieties, a commercially-acceptable threshold of 30% injury required between 3.4 to more than 10 times the PoaCure® rate needed for annual bluegrass control. Results from herbicide efficacy and tolerance studies indicate that PoaCure® 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. In addition to being difficult to control and aesthetically unpleasing to view, annual bluegrass has also long been blamed for missed golf putts. Some researchers have surmised that a golf ball's direction may be altered when the ball traverses an anomaly in the greens surface, such as annual bluegrass, but no scientific studies have tested this assumption. 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. Study results suggest that an isolated patch of annual bluegrass increases ball directional imprecision by 8 mm m^-1 compared to visibly-pure creeping bentgrass and that tools and methodology currently reported in scientific literature are not precise enough to discern these subtle changes in direction. At Virginia Tech, we devised a new methodology to discern subtle changes in ball roll directional precision and bounce as influenced by an isolated patch of annual bluegrass in an otherwise visually-pure creeping bentgrass canopy. We used a mechanical putter to minimize directional errors associated with commercially-available simulated putt-devices, selected balanced golf balls, eliminated legacy of repeated ball rolls by brushing putting green surface canopy between ball rolls, scored ball direction prior to terminal acceleration with pressuresensitive paper, and used high-speed video and motion tracking software to measure ball wobble and bounce. Results indicate that annual bluegrass increases directional imprecision and bounce of golf balls rolling across a greens canopy.