Application Timing Affects Tolerance of Zoysiagrass to Fluazifop‐P‐butyl and Safening Effect of Triclopyr

Abstract

1789 RESEARCH Z oysiagrass (Zoysia spp.) is a warm-season turfgrass widely adopted in the transitional zone and southeastern regions of the United States due to good turf quality and low nutrient input requirements. Zoysiagrass exhibits more shade and winterkill tolerance than bermudagrass (Cynodon spp.), fewer disease and insect problems than St. Augustinegrass [Stenotaphrum secundatum (Walter) Kuntze], and moderate salinity tolerance and wear tolerance compared with other warm-season grasses (Patton, 2010;Patton et al., 2017a). The most troublesome weeds in zoysiagrass turf are frequently other warm-season grasses with a similar growth habit and growing season. For example, bermudagrass is often one of the most problematic weeds to control, especially for golf courses during the process of transitioning from bermudagrass to zoysiagrass fairways ( Johnson, 1992). Use of nonselective herbicides for long-term bermudagrass control is usually not practical and can be costly, since bermudagrass will eventually regrow from rhizomes and compete with the zoysiagrass ( Johnson and Carrow, 1995). The aryloxyphenoxyproponiate (AOPP) herbicide fluazifop-P-butyl is labeled for bermudagrass suppression in zoysiagrass; however, previous studies reported significant injury to zoysiagrass despite nearly 100% control of bermudagrass ( Johnson, 1987). Finding ways to increase the rate of AOPP ABSTRACT Aryloxyphenoxypropionate (AOPP) herbicides, such as fluazifop-P-butyl, can be used for postemergence control of grassy weeds in zoysiagrass (Zoysia spp.), although the turf might suffer transient injury. This injury can be reduced by tank mixing fluazifop-P-butyl with triclopyr, an herbicide that behaves as a safener for AOPP herbicides. To characterize seasonal variation in zoysiagrass injury caused by fluazifop-P-butyl and triclopyr applications, we conducted a 2-yr study on three Zoysia spp. cultivars ('Empire', 'Geo', and 'Zeon') at Jay, FL, from August 2015 to April 2017, evaluating how injury and turf quality were affected after spring, summer, and fall applications. The level of injury and changes in turf quality were influenced by fluazifop-Pbutyl application timing, but the most sensitive season varied with the cultivar. The seasons with the greatest injury were also the ones in which the safening activity of triclopyr was most effective. In addition, when triclopyr was applied with fluazifop-P-butyl, the quality of all evaluated cultivars recovered to the level of nontreated controls by 2 wk after treatment. Nonstructural carbohydrate content was not affected by herbicide applications, but there were major differences in glucose and starch content between above-and belowground tissue depending on cultivar and season. Overall, our study confirmed that tank mixing triclopyr can reduce fluazifop-P-butyl phytotoxicity in zoysiagrass, and in the case of relatively tolerant cultivars, it might allow the use of rates higher than the current labeled rate with little negative impact on turf quality while providing better control of ...

Transgressive segregation and maternal genetic effects of non–target site fluazifop-P-butyl tolerance in Zoysia spp.

“…However, as with most traits controlled by multiple mechanisms, environmental conditions also inevitably play a role in the outcome of herbicide applications, and fluazifop-P-butyl sensitivity in zoysiagrass has been documented to vary depending on the environment and time of the year (Liu et al. 2019b). This significantly increases the difficulty of breeding a commercial line that performs predictably under variable environmental conditions or during different times of the year.…”

“…Because the tolerance is a polygenic trait, research should be conducted to identify the responsible QTLs to enable the use of marker-assisted selection and avoid the need to regularly conduct herbicide-sensitivity screenings (Délye et al 2011;Gupta et al 2010;Schneider et al 1997). However, as with most traits controlled by multiple mechanisms, environmental conditions also inevitably play a role in the outcome of herbicide applications, and fluazifop-P-butyl sensitivity in zoysiagrass has been documented to vary depending on the environment and time of the year (Liu et al 2019b). This significantly increases the difficulty of breeding a commercial line that performs predictably under variable environmental conditions or during different times of the year.…”

Variation in tolerance mechanisms to fluazifop-P-butyl among selected zoysiagrass lines

“…Another challenge is the stability of the tolerance trait. Liu et al (2017) reported that fluazifop-P-butyl injury varied depending on the time of the year when the application is made and that the magnitude of this seasonal effect on herbicide susceptibility was also influenced by the cultivar. Even if a line with a single tolerance mechanism were to be generated, the complex nature of fluazifop-P-butyl tolerance may lead to unstable phenotypes due to large genotype by environment interactions, and thereby may limit their commercial value.…”