Effect of temperature and heat units on zoysiagrass response to herbicides during post-dormancy transition

Abstract

In the transition zone, turfgrass managers generally utilize dormancy period of warm-season turfgrass to apply herbicides for managing winter annual weeds. Although this weed control strategy is common in bermudagrass, it has been less adopted in zoysiagrass (Zoysia spp.) due to variable turfgrass injury during post-dormancy transition. Previous research reported that air temperature could affect weed control and crop safety from herbicides. Growth chamber studies were conducted to evaluate zoysiagrass response to glyphosate and glufosinate as influenced by three different temperature regimes during and after treatment. A field research study was conducted at four-site years to assess the influence of variable heat unit accumulation on zoysiagrass response to seven herbicides. In the growth chamber study, glufosinate injured zoysiagrass more than glyphosate and reduced time to reach 50% green cover reduction, regardless of the rate when incubated for 7 d under different temperature levels. When green zoysiagrass sprigs were incubated for 7 d at 10 C, the rate of green cover reduction was slowed for both herbicides; however, green cover was rapidly reduced under 27 C. After incubating treated zoysiagrass plugs having 5% green cover at 10 C for 14 d, glyphosate-treated plugs reached 50% green cover in 22 d similarly to nontreated plugs but less than the 70 d required for glufosinate-treated plugs. Zoysiagrass response to glyphosate was temperature dependent, but glufosinate injured zoysiagrass unacceptably regardless of temperature regime. Diquat, flumioxazin, glufosinate, and metsulfuron+rimsulfuron injured zoysiagrass at 200 or 300 growing-degree-day at base 5 C (GDD5C) application timings, but foramsulfuron and oxadiazon did not injure zoysiagrass regardless of GDD5C. The relationship of leaf density to green turf cover is dependent on zoysiagrass mowing height and both metrics are reduced by injurious herbicides. Research indicates that glufosinate injures zoysiagrass more than glyphosate, and speed and magnitude of herbicide injury generally increases with temperature.

Regional response of zoysiagrass turf to glufosinate and glyphosate applied during postdormancy transition based on accumulated heat units

“…Zoysiagrass response to glyphosate is generally acceptable when turf is treated not later than 200 GDD 5C . Craft et al (2023) demonstrated that the magnitude of herbicide injury on zoysiagrass after glyphosate application is temperature dependent, while glufosinate-injured turfgrass, regardless of temperature prevalent during application timing. Three times more glufosinate absorbed into zoysiagrass leaves compared to glyphosate and both herbicides absorbed more readily into stolons compared to leaves (Craft 2021).…”

“…However, when zoysiagrass was mown at 6.5 cm at the other four site years, zoysiagrass had 91 green leaves dm −2 (Figure 2). Previous research conducted in Blacksburg, VA, on turf mown within the same height ranges indicates that the 237 green leaves dm −2 at 1.9 cm height of cut (HOC) would result in 39% green turf, and the 91 green leaves at 6.5 cm HOC would result in 20% green turf cover of zoysiagrass (Craft et al 2023). These estimates agree with the actual observed green cover at 350 GDD 5C , which averaged 49% and 18% over the 4 site years each for turf maintained at 1.8 and 6.5 cm, respectively (data not shown).…”

“…Growth and development of zoysiagrass based on the GDD has been reported (Patton et al 2004), but restricted to limited geographical regions. Although zoysiagrass response to glyphosate and glufosinate has differed based on accumulated GDDs in Virginia (Craft et al 2023) and in Italy (Rimi et al 2012), regional variations in factors such as seasonal precipitation legacy (Shen et al 2015) and winter severity (Schwab et al 1996) have altered plant responses between locations. Therefore, the objective of this study was to evaluate zoysiagrass turf response to glyphosate and glufosinate when applied at four GDD-based application timings spanning the period before and during the postdormancy transition of zoysiagrass at different sites in the transition zone and warm climatic region of the United States.…”