Annual bluegrass (ABG) (Poa annua L.) is a prolific seed producer in the spring on golf courses that in turn decreases aesthetic quality and trueness of ball roll on coolseason putting greens. Proxy (ethephon) applied twice in the spring after green-up is the current industry standard after the loss of Embark (mefluidide) from the turf and ornamental market. However, plant growth regulators including Proxy have been used for years to help suppress ABG seedheads with inconsistent success. The primary objective of this study was to determine if ABG seedhead suppression is improved by adding a late fall application of Proxy to the two traditional spring applications of plant growth regulators at nine locations with diverse environments. A second objective was to determine the importance of including Primo Maxx (trinexapac-ethyl) in fall and spring applications. Adding a late fall application of Proxy prior to the two spring applications (F+S+S) improved control of ABG seedheads over the traditional two spring applications (S+S), but the magnitude of improvement varied among locations. Abbreviations: ABG, annual bluegrass; AUSCPC, area under seedhead cover progress curve; CBG, creeping bentgrass; DAISA, days after initial spring application; F+S+S, Proxy + Primo Maxx applied once in fall plus twice in spring; GDD, growing degree day; S+S, Proxy + Primo Maxx applied twice in spring. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.

Fall N fertilizers are applied to turfgrass at predetermined rates instead of being based on plant-N status. Normalized difference vegetative index (NDVI) and the sufficiency index (SI) concept are used to assess plant-N status in some agronomic crops but has not been evaluated for turfgrass. This study was conducted across 3 yr in Connecticut to determine fall and spring NDVI SI values in a mixed species, cool-season lawn. Field experiments were set out with varying fall N rates with NDVI measured weekly in October and November, and in late April. Quadratic and Linear-Response and Plateau (LRP) models were significant (P < .0001) for all fall and spring SI values in response to fall N rates. Fall SI was maximized between 140 and 155 kg N ha −1 for the quadratic model and plateaued between 79 and 102 kg N ha −1 for the LRP model. Spring SI was maximized at 189 and plateaued at ≥116 kg N ha −1 for quadratic and LRP models, respectively. In relation to commonly recommended fall N rates of 24.5, 49, and 98 kg N ha −1 , the models suggest that no supplemental N is needed when SI is ≥92, ≥95, and ≥99% of the N-rich reference in the fall, respectively. Late April SI >89% of spring N-rich reference would indicate that excess fertilizer was applied the previous fall at rates >49 kg N h −1. The NDVI SI can provide site-specific fall N fertilization guidance of cool-season turfgrass lawns.

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Cold deacclimation sensitivity has been cited as an important factor associated with winterkill susceptibility of annual bluegrass (Poa annua L.). Increased potential for deacclimation for this species has been attributed to higher metabolic activities in response to warm winter temperatures. We hypothesized that using plant growth regulators to inhibit turfgrass growth and metabolism during winter months could potentially suppress premature deacclimation and increase survival of annual bluegrass. The specific objectives of this study were to examine the effects of varying rates of autumn-applied trinexapac-ethyl (TE) and prohexadione-Ca (PC) on winter hardiness and spring recovery of an annual bluegrass putting green. The study was conducted over the winters of 2015-2016 and 2016-2017. Treatments included an untreated control and four rates of TE (0.05, 0.10, 0.2, and 0.4 kg a.i. ha -1 ) and PC (0.06, 0.12, 0.25, and 0.50 kg a.i. ha -1 ). Freezing tolerance was assessed based on controlled freeze tests to estimate the lethal temperature resulting in 50% regrowth (LT 50 ). General turfgrass health was also assessed based on visual turf quality and normalized difference vegetation index (NDVI). Late-autumn PGR applications impacted the freezing tolerance of annual bluegrass during Year 1, but no treatment effects were detected in Year 2. Plant growth regulator treated turf, pooled over chemicals and rates, exhibited lower freezing tolerance (Year 1), turf quality, and NDVI (Years 1 and 2) compared to untreated turf particularly at the higher application rates. By the end of May in both years, all treatments recovered to the same levels. INTRODUCTIONAnnual bluegrass (Poa annua L.) in high maintenance turf is often considered a problematic weed (Huff, 2003). Annual bluegrass is sensitive to a range of abiotic and biotic stresses,