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BACKGROUND Annual bluegrass is a troublesome weed in managed turf systems. A survey was conducted to evaluate the prevalence of herbicide resistance in golf course populations of annual bluegrass in eastern Texas. Screenings were conducted for two photosystem II (PS II)‐inhibitor herbicides [simazine preemergence (PRE), amicarbazone postemergence (POST)], two acetolactate synthase (ALS) inhibitors (foramsulfuron POST, trifloxysulfuron POST) and one microtubule assembly inhibitor (pronamide PRE/POST). RESULTS Ninety percent of the populations were found to be resistant to at least one of the tested herbicides. The TX15‐14 population was >490‐, 178‐, 10‐, 26‐, 4.3‐ and 3.8‐fold, and the TX15‐27 population was >490‐, 16‐, 28‐, 84‐, 5.2‐ and 4.1‐fold less sensitive to simazine, amicarbazone, foramsulfuron, trifloxysulfuron, pronamide POST and pronamide PRE, respectively, compared to the susceptible standard TX15‐SUS. Populations resistant to pronamide POST were completely controlled by pronamide PRE at the label recommended rate. The ALS and psbA gene sequence analysis indicated the presence of target site mutations (Ser‐264‐Gly in the psbA gene of TX15‐14 and Trp‐574‐Leu in the ALS gene of TX15‐27). However, given the absence of any target‐site mutation in the ALS gene of TX15‐14, the psbA gene of TX15‐27 and α‐tubulin of both populations, nontarget site mechanisms of resistance are suspected. CONCLUSION This is the first case of multiple herbicide resistance in annual bluegrass populations to three herbicide modes of action. Results show the widespread occurrence of multiple herbicide resistance in golf course annual bluegrass populations in eastern Texas and emphasize the need for the development and implementation of effective resistance management practices. © 2020 Society of Chemical Industry

Municipal water restrictions across the southern and southwestern United States have created additional challenges for maintaining safe playing surfaces on recreational turf facilities. In recent years, many cities within these regions have begun to impose irrigation restrictions during winter months. Although winter overseeding has been regularly practiced in these areas, interest and use of colorants as an alternative to overseeding has grown due to decreasing water availability and budget concerns. Data on relative performance of colorant-treated vs. overseeded dormant turf would be of interest to turf managers, because colorants may be more cost-effective and require less water than winter overseeding. The objectives of this 2-year field study were to evaluate effects of winter treatments on performance (green cover, surface hardness, and soil moisture attributes), turfgrass injury resulting from simulated traffic, and spring transition of ‘Tifway’ bermudagrass (Cynodon dactylon L. × Cynodon transvaalensis Burtt-Davy) under a 1-day per week irrigation schedule. Treatments included 1) untreated bermudagrass, 2) fall colorant-treated bermudagrass, 3) perennial ryegrass (Lolium perenne L.) overseeded bermudagrass, and 4) turf-type annual ryegrass (Lolium multiflorum Lam.) overseeded bermudagrass. In both years, treatment differences were detected for percent green cover, soil volumetric water content (VWC), percent visual turfgrass injury, surface hardness, and percent bermudagrass transition. Percent green cover and visual turfgrass injury levels were similar between annual and perennial ryegrass in year 1, whereas loss of green cover and greater turfgrass injury were noted in annual ryegrass during the spring of year 2. Residual benefits of fall colorant applications extended into February of year 1, but dissipated by late December of year 2, likely due to higher rainfall and warmer temperatures, which prevented full bermudagrass shoot dormancy. Overseeding reduced bermudagrass spring transition by up to 50% compared with untreated and colorant-treated plots. Fall colorant treatments did not accelerate bermudagrass transition compared with untreated plots. Results of the study demonstrate that environmental differences from season to season can impact the relative benefits derived from colorant applications, as well as the performance of annual and perennial ryegrass.

Phoma macrostoma is a bioherbicide being developed for selective weed control in turfgrass. The previous research with this product is limited to cool-season turfgrass systems with little information available on appropriate application rates or weed control spectrum for weeds common to warm-season turf. Studies were conducted to evaluate application rates and weed control spectrum of P. macrostoma on common dandelion (Taraxacum officinale G.H. Weber ex Wigg.), slender aster (Aster subulatus var. ligulatus Shinners), common mallow (Malva neglecta Wallr.), common purslane (Portulaca oleracea L.), California burclover (Medicago polymorpha L.), and annual sow thistle (Sonchus oleraceus L.). Although most weeds exhibited susceptibility to P. macrostoma, control differed by weed species and study. P. macrostoma had the greatest efficacy on dandelion, but provided little efficacy on common purslane and common mallow. Warm-season turfgrass tolerance was also evaluated across five commonly used warm-season turfgrass species. No turfgrass injury was observed at any rate on any species; however, weed control data suggest that P. macrostoma may not offer effective broadspectrum weed control similar to common synthetic herbicides, when applied at the rates used in this study.

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Shade is a major problem facing turf managers worldwide. Availability of low-cost devices and methods for quantifying daily light integral (DLI) offer the turf manager the ability to more precisely determine DLI levels in shade, yet minimal DLI requirements for acceptable turf quality (DLI m ) for many commonly used warm-season turf cultivars grown under longer-term chronic shade stress have not been extensively tested. The objectives of this 2-yr field shade study were to (a) determine effects of growth regulator trinexapac-ethyl (TE) and season (summer or fall) on DLI m of nine commercially available bermudagrass (Cynodon spp.) and zoysiagrass (Zoysia spp.) cultivars; (b) determine effects of shade level and TE on summer percent green cover and root growth; and (c) determine effects of shade treatments on soil temperatures across the growing season. Significantly higher DLI m were noted during summer compared to fall for all cultivars in the study. The DLI m were generally higher for bermudagrass than zoysiagrass cultivars. 'Tifway' required the highest DLI m (ranging from 23.5 to 27.2 mol m −2 d −1 ) of the bermudagrasses. 'TifGrand', 'Celebration', and 'Latitude 36' showed comparable DLI m during summer and fall. Fewer consistent differences were detected between zoysiagrasses, with 'Zorro' and 'Zeon' showing the lowest summer DLI m (18.1 and 19.1 mol m −2 d −1 , respectively) and 'Geo' showing the lowest fall DLI m (11.7 mol m −2 d −1 ). Trinexapac-ethyl reduced DLI m only in Zorro, 'Palisades', and 'JaMur' zoysiagrass, but had no effect on bermudagrass DLI m . The DLI m for a number of cultivars were higher than those previously reported in the literature, which may be attributed to lower mowing heights and/or use of permanent shade structures that were not removed for the duration of the 27-mo study. The findings should benefit turf managers by guiding data-driven, seasonalbased, warm-season turfgrass cultivar selection for shaded environments.

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