Zoysiagrass and weed response to herbicides during post-dormancy transition

Abstract

Winter annual weeds begin to germinate as zoysiagrass enters winter dormancy in autumn. These weeds can suppress zoysiagrass shoot development the following spring through competition for sunlight, moisture, and nutrients. Previous research involving winter annual weed control in dormant turfgrass has been conducted primarily on bermudagrass, but less is known about how various herbicides used for this purpose will influence zoysiagrass post-dormancy transition. Two field studies were conducted at 7 site yr between 2016 and 2020 to evaluate 17 herbicide treatments that are typically marketed for broadleaf weed control in spring and 18 herbicide treatments that are typically marketed for annual bluegrass control during winter for effects on a variety of weeds and semi-dormant ‘Meyer’ and dormant ‘Zeon’ zoysiagrass, respectively. Glufosinate, glyphosate + simazine, and indaziflam + simazine controlled Persian speedwell over 90% and significantly higher than auxin-type and other herbicide combinations evaluated. The combination of simazine and glyphosate had better dandelion and Persian speedwell control than glyphosate applied alone. Glufosinate controlled dandelion, hairy bittercress, and Persian speedwell more effectively than glyphosate. In ‘Meyer’ zoysiagrass, glyphosate and glufosinate controlled annual bluegrass equivalently while in ‘Zeon’ zoysiagrass, glyphosate controlled annual bluegrass more than glufosinate. Foramsulfuron or simazine containing treatments controlled annual bluegrass >90%. Flumioxazin admixture with diquat, glufosinate, or glyphosate improved annual bluegrass control. Herbicide treatments containing diquat, glufosinate, glyphosate, and metsulfuron alone or in a tank-mix should not be applied to ‘Meyer’ zoysiagrass with 5% visual green turf cover due to high injury potential. In both studies, glufosinate was more injurious to ‘Meyer’ and ‘Zeon’ zoysiagrass than glyphosate. Overall, several herbicides that control annual bluegrass or broadleaf weeds can be safely applied to ‘Zeon’ zoysiagrass during dormancy or ‘Meyer’ zoysiagrass during post-dormancy transition.

Factors influencing subcanopy leaf and stolon exposure and associated absorption and translocation of herbicides in semidormant zoysiagrass

“…However, it has been noted that close inspection of dormant zoysiagrass can reveal green tissue at the base of stems and subcanopy leaves that are at least partially green (Velsor et al 1989). Nonselective herbicides, such as glyphosate or glufosinate, are commonly used to control winter weeds in dormant turfgrass, but only five peer-reviewed articles have reported dormant-zoysiagrass response to these herbicides (Craft et al 2023a;Hoyle and Reeves 2017;Rimi et al 2012;Velsor et al 1989;Xiong et al 2013). These five articles indicate that glyphosate and glufosinate did not injure zoysiagrass when treated "prior to green-up" or "during dormancy."…”

“…Despite evidence of glyphosate and glufosinate being safely applied to dormant zoysiagrass (Craft et al 2023a) and product labels for these herbicides indicating their use on "dormant turfgrass," turfgrass managers are hesitant to use nonselective herbicides on dormant zoysiagrass. Extension bulletins from Arkansas and Tennessee recommend against treating dormant zoysiagrass with glyphosate (Boyd 2016;Brosnan and Breeden 2011).…”