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Xi Xiong, Ken Diesburg and Daniel T. Lloyd

Winter application of glyphosate on dormant zoysiagrasses (Zoysia spp.) is a common practice for control of fall-emerging weeds in the upper transition zone. However, repeated application can lead to selection of resistant weed populations. This study evaluated glufosinate, another non-selective herbicide, for weed control and safety on dormant zoysiagrass turf. Field plots were established on three sites during two growing seasons. At two application timings, glufosinate at rates of 0.84 or 1.68 kg·ha−1 were compared with glyphosate at 0.56 kg·ha−1 and a nontreated control. Application timings included 2 to 3 weeks or 2 to 3 days before zoysiagrass spring green-up. Regardless of rate, glufosinate was similar in effectiveness to glyphosate for control of annual bluegrass (Poa annua L.) and mouseear chickweed (Cerastium vulgatum L.). Application timing significantly affected phytotoxicity on zoysiagrass turf. For applications at 2 to 3 weeks before initiation of zoysiagrass green-up in spring, no negative impact on zoysiagrass was found. However, when applications were made within days of zoysiagrass resuming growth, both glufosinate and glyphosate reduced turf quality up to 40%. This study suggests that glufosinate can be an alternative to glyphosate for weed management on dormant zoysiagrass turf, but applications should be timed at least 2 weeks before initiation of spring growth.

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Daniel T. Lloyd, Douglas J. Soldat and John C. Stier

Fall fertilization of turfgrass in northern climates is often considered to be agronomically beneficial, although research on nitrogen (N) uptake during cold temperatures is sparse and environmental concerns exist regarding nitrate leaching. Therefore, the objective of this study was to evaluate N uptake potential, use, and plant metabolic response in a climate-controlled environment evaluating the responses of various cool-season turfgrass species to variable N rates and temperature regimens. Creeping bentgrass (Agrostis stolonifera L.), kentucky bluegrass (Poa pratensis L.), and annual bluegrass (Poa annua var. reptans L.) were seeded and grown for 3 months and then acclimated in a growth chamber to one of three climate regimens corresponding to 15 Sept., 15 Oct., and 15 Nov. in Madison, WI. Grasses were fertilized at 0, 25, 49, or 98 kg·ha−1 N with 15N-labeled ammonium sulfate (10 atom % 15N) by applying a liquid solution of 75 mL per pot (1 cm of solution in depth). Data collected included verdure biomass, root mass, net canopy photosynthesis, and 15N fertilizer uptake. For all turfgrass species, shoot growth increased in response to N application in the September regimen, but not in October or November regimens. N uptake was significantly lower in the November regimen compared with September with an average of 73% of fertilizer recovery in September compared with 57% and 38% in October and November, respectively. Root mass and net canopy photosynthesis were greatest in the November treatments, although these responses were generally unaffected by N application rate. The results of this study indicate that N uptake capacity is greatly reduced as average daily temperatures approach 0 °C. Nitrogen application rates should be adjusted downward to maximize uptake efficiency in cold temperatures.