In 2011, Poa annua L. (Poa) biotypes were collected from greens of two golf courses in Lexington, Kentucky: 1.) The Lexington Country Club (LCC) and 2.) The University Club (UC). The samples were collected based on exhibiting one of two appearances while on the same green: 1.) dark green, with few to no flower heads (dark biotype) or 2.) light green, with numerous flower heads (light biotype). Two PGRs, paclobutrazol and flurprimidol, and two herbicides, bispyribac-sodium and amicarbazone, were applied to the plants both in the field and the greenhouse. Quality ratings were recorded weekly in both the field and greenhouse and grass clippings were collected and measured weekly in the greenhouse. Flurprimidol controlled the dark biotypes and paclobutrazol controlled the light biotypes in the field in 2011. However, only location by treatment interactions were in 2012; flurprimidol, bispyribac-sodium, and amicarbazone controlled the biotypes from the LCC while paclobutrazol controlled the biotypes from UC. In the greenhouse study there was a significant three way interaction between color, location, and treatment for quality. PGRs controlled the light biotypes from LCC and the dark biotypes from UC. Herbicides controlled the light biotypes more than the dark, however, the light biotypes recovered after amicarbazone treatments. PGRs reduced clipping weights of the dark biotypes more than the light and herbicides reduced clipping weights of the light biotypes more than the dark. Both PGRs and herbicides reduced clipping weights of the Poa collected from the LCC more than UC. These results demonstrate both the potential for differential responses between Poa biotypes to PGRs and herbicides and that these differences, like all things about Poa, may be complex. A laboratory experiment was also designed to examine the absorption and potential metabolism of 14C-labeled flurprimidol in creeping bentgrass (Agrostis stolonifera (L.)), bermudagrass (Cynodon dactylon (L.)), Kentucky bluegrass (Poa pratensis (L.)), perennial ryegrass (Lolium perenne (L.)), tall fescue (Festuca arundinacea (Schreb.)), and zoysiagrass (Zoysia japonica (Steud.)) and light and dark Poa biotypes collected from golf greens. Flurprimidol absorption and translocation was greater for warm season grasses than cool season grasses. Only parent flurprimidol was detected in all turf species.

Annual bluegrass (Poa annua L.) is a problematic weed in turfgrass that has evolved resistance to twelve different herbicide sites of action. The mitotic-inhibiting herbicide pronamide has both pre- and post-emergence activity on susceptible annual bluegrass populations. Still, post-emergence activity may be compromised in some resistant populations due to the lack of root uptake or an unknown foliar resistance mechanism. Spray droplet size may affect foliar and soil deposition of pronamide, thus potentially explaining variation in population control or differential foliar and root uptake. Pronamide, flazasulfuron, and pronamide + flazasulfuron deposition were quantified on annual bluegrass as affected by spray-droplet size. The efficacy of these herbicide treatments in resistant (R) and susceptible (S) annual bluegrass populations was then evaluated with two droplet sizes (400 and 1000 μm). Absorption and translocation of pronamide were investigated in R and S populations following foliar-only and soil-only pronamide applications.

Allelopathy occurs when one organism releases a compound into the environment that affects the functioning of another organism. Scientists have long suspected that alleopathic plant compounds could offer novel, softer chemistries to the ongoing battle of controlling pests in agricultural fields. Strawberry growers rely on toxic fumigants to kill soilborne fungal pests, weeds, nematodes, and insects. Increased regulations have reduced the use of fumigants (including methyl bromide), and strawberry growers need new sustainable pest control solutions. We selected four putative allelochemicals with known fungicidal and herbicidal activity (ferulic acid, gallic acid, juglone, and p-Coumaric acid). We assessed the pesticidal activity of these plant compounds both in agar and in soil on two emerging soilborne fungal pathogens (Macrophomina phaseolina and Fusarium oxysporum f.sp. fragariae), and four annual weeds commonly found in strawberry production fields (Malva parviflora, Melilotus officinalis, Poa annua, and Senecio vulgaris). We also assayed lettuce (Lactuca sativa ‘Inferno’), which served as a positive control plant species due to its sensitivity to phytotoxic compounds. Fitted sigmoidal dose-response curves predicted EC50 and EC75 values for each combination of plant compound and pest. All plant compounds inhibited the in vitro radial mycelial growth of the two soilborne fungal pathogens in a dose-dependent manner. Fusarium oxysporum f.sp. fragariae was more sensitive to the plant compounds than Macrophomina phaseolina. Average EC50 values for the radial mycelial growth of two F. oxysporum f.sp. fragariae isolates were 75.1 parts per million by weight (ppmw) juglone, 469 ppmw p-Coumaric acid, and 687 ppmw ferulic acid. Average EC50 values for the radial mycelial growth of two M. phaseolina isolates were 196 ppmw juglone, 2869 ppmw p-Coumaric acid, and 5716 ppmw ferulic acid. The three compounds we assayed in vitro also reduced M. phaseolina colony forming unit counts in soil and the EC50 values were 476 ppmw ferulic acid, 612 ppmw juglone, and 827 ppmw p-Coumaric acid. Metconazole, the conventional fungicide control, did not inhibit M. phaseolina colony forming unit counts in soil at its label high rate. The plant compounds required similar or lower rates to inhibit colony forming units that grew from M. phaseolina overwintering structures (microsclerotia) in soil as to inhibit radial mycelial growth in vitro. Based on the EC50 value in soil assays, ferulic acid was the least expensive plant compound to apply on a per acre basis to inhibit M. phaseolina ($74,226). In F.oxysporum f.sp. fragariae soil assays, the compounds induced hormesis at lower rates and may be germination stimulant candidates. Metconazole and the high rates of every compound effectively or completely inhibited F. oxysporum f.sp. fragariae colony forming units in soil. The plant compounds were more herbicidal than fungicidal in vitro. When combining the in vitro seedling length results for L. sativa, M. parviflora, P. annua, and S. vulgaris the EC50 values differed significantly (p < .0001) and were: 47 ppmw juglone, 120 ppmw p-Coumaric acid, 189 ppmw ferulic acid, and 297 ppmw gallic acid. At least one rate of ferulic acid, juglone, and p-Coumaric acid inhibited the germination of all plant species, while gallic acid only inhibited the germination of P. annua at 1000 ppmw (p < .05). In soil, visible microbial contamination in individual wells of 24-well plates and seed dormancy made it difficult to fit curves to weed seedling length data. The soil assay L. sativa seedling length EC50 values 11 days after initial treatment were slightly higher than in vitro, although plant compounds were in the same order of phytotoxicity: 129 ppmw juglone, 616 ppmw p-Coumaric acid, 644 ppmw ferulic acid, and 1584 ppmw gallic acid. Based on the EC50 value in soil assays, the least expensive compound to inhibit L. sativa seedling length on a per acre basis was gallic acid ($21,676). Germination 26 days after initial soil treatment generally declined in a dose-dependent manner for each compound. There was a direct relationship between plant compound rate and seedling damage in soil with the higher rates of all compounds, except p-Coumaric acid, inducing damage comparable to a conventional herbicide (pendimethalin or oxyfluorfen). Contaminated treatments appeared to be due to an interaction between plant compounds and microorganisms because herbicide and water controls had almost no microbial growth 11 days after initial treatment. Further, there was a significant positive linear relationship between level of contamination in phenolic acid-treated wells (ferulic acid, gallic acid, and p-Coumaric acid, p < .0001) and the in soil rate. This relationship was slightly negative in juglone soil treatments (p = .0167), which may be due to its greater antimicrobial activity than the phenolic acids. We propose that herbicidal effects in soil were due to the joint effect of the plant compounds themselves, and the microbial growth in wells. Microbial growth was either antagonistic or additive to the inhibitory action of the plant compounds. The plant compounds we assayed were inhibitory of emerging fungal pathogens in strawberry production and common annual strawberry field weeds. Evidence presented in this thesis correlates well with past research that not only found plant compounds to be herbicidal and fungicidal, but also described their modes-of-action (such as the production of reactive oxygen species that causes necrotic lesions on roots, and inhibition of glycolytic enzyme activity that prevents germination), and implicate plant compounds as carbon sources for a variety of microorganisms. Compound prices are currently exorbitant, but may decline as demand increases. Whether or not they provide effective pest control may depend on soil texture, organic matter, microbial diversity, and other edaphic factors.

<p>  </p> <p>Annual bluegrass (<em>Poa annua</em> L.) is the most troublesome weed in turfgrass systems and the second most troublesome weed across all grass crops. Controlling annual bluegrass is exceptionally complicated due to its high genetic adaptability to new environments. Additionally, prolific seed production allowed the rapid development of herbicide resistance to 12 herbicide modes of action. Experiments were initiated with the goal to better understand annual bluegrass ecology and resistance to ethofumesate. A dose-response experiment was initiated in 2022 to determine the potential level of ethofumesate resistance in annual bluegrass collected from seed production systems. Seed from 55 annual bluegrass populations was obtained from three sources: seed production fields (31 populations), seed cleaning process (6 populations), and seed testing prior to retail distribution (18 populations). </p> <p>Individual seedlings (2–3 tillers) were treated with ten doses of ethofumesate: 0, 0.6, 1.1, 2.8, 5.6, 8.4, 11.2, 16.8, 22.4, and 44.8 kg ai ha−1; with 1.1 to 2.2 kg ha−1 as the label application rates for perennial ryegrass (<em>Lolium perenne</em> L.). The resistance to susceptible ratio of populations across all sources ranged from 0.48 to 5.48. The most resistant populations from production fields, removed during the seed cleaning process, or found in seed testing lots had ED50 values of 12.1, 13.1, and 9.4 kg ai ha−1, respectively. Further, 68% of the populations found in production fields had ED50 higher than 6 kg ai ha−1, which indicates that annual bluegrass resistance is common in grass seed production. A garden study was initiated in November 2020 to assess the development, reproduction, and survival of ten annual bluegrass populations in Indiana. Annual bluegrass plants were maintained in the absence of turf competition and not subjected to typical turfgrass management practices including irrigation, mowing and fertilization. Data collected in included growth rate, biomass production, ground cover, morphology, flowering time, seed production and morphology, and both winter survival and subsequent summer survival of plants. Principal component analysis indicated that certain populations grouped together based on their development, morphology, stress tolerance, and seed production. Plants from the cooler climates (OR, PA, and IN) were characterized by higher growth rates and biomass compared to southern ecotypes. These three populations survived the longest during the summer, with the PA population averaging the highest ground cover of 276 cm2 on 23 July 2021. Plants from warm climates (AL, FL, NC, SC, TN, TX) had poor summer survival. Additionally, the FL population had the highest winterkill of 68%, followed by TX at 45%. The NJ population was distinct from other populations, and plants had robust aboveground biomass and high seed production. The results indicate that the development, reproduction, and survival of different annual bluegrass biotypes are dependent on the climate of origin. A third experiment was designed to understand patterns of germination and seed longevity in populations from five climates across the U.S. at two depths of burial. Seed was retrieved in 6-month intervals up to 24 months. Seed viability by depth (surface vs. 5-cm deep) of burial differed only 18 months after the initiation of the study. However, seed viability did differ among populations on each date of seed retrieval. Viability was low ranging from 0.21 to 0.91%, and populations originating from cool climates (New Jersey, Pennsylvania, and Oregon) generally had higher viability than populations originating from warmer climates. Annual bluegrass seed tested in this study typically had low levels of survival (<0.5%); however, all populations retained some level of viability 24 months after burial, which would allow future reproduction of this troublesome weed. Overall, this research determined that herbicides alone will likely be ineffective at controlling annual bluegrass and that knowledge of the development, reproduction, and survival of local annual bluegrass populations should be factored into an integrated weed management strategies created for each site. </p> <p>  </p>

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.