Suppressing zoysiagrass in cool-season turf

Figure 1 Zoysiagrass can encroach into cool-season rough and is easily recognizable by golfers in winter months. (Photo: Aaron Patton)

Zoysiagrass (Zoysia japonica) is a desirable turfgrass for golf courses in the Transition Zone because of its low maintenance requirement, but it can become invasive when it spreads via rhizomes and stolons into adjacent areas where it is unwanted. Further, some golfers and superintendents find the winter dormant color undesirable when patches of zoysiagrass exist in a stand of cool-season grasses (Figure 1).

Previous attempts to control zoysiagrass with the nonselective herbicide glyphosate were successful when two or more applications were made in a season or when 2 lbs. ae/A or more (equivalent to 2.7 quarts/A or more of a 41-percent glyphosate formulation) was used in a single application. However, no selective herbicide is registered for use to control zoysiagrass in cool-season turf. The objective of this experiment was to evaluate the efficacy of two 4-HPPPD-inhibiting herbicides, Pylex (topramezone, BASF) and Tenacity (mesotrione, Syngenta), and a lipid synthesis inhibitor, Prograss (ethofumesate, Bayer Environmental Science), for selectively controlling zoysiagrass in cool-season turf with fall applications.

Table 1 (See below for explanation)

Herbicide assessment on zoysia

Field experiments were conducted at the W.H. Daniel Turfgrass Research and Diagnostic Center in West Lafayette, Ind., in 2013-2014, 2014-2015 and 2015-2016 in separate but adjacent areas. The soil at the location was a Mahalasville-Treaty silty clay loam with a pH of 6.8 and 3.5 percent organic matter. The experimental area was a mature stand of Zen 500 zoysiagrass (Zoysia japonica) planted by seed in 1998. Plots were mown weekly at 2 inches during the experiment.

The design for this experiment was a randomized complete block with three (year 1) or four (years 2 and 3) replications and 25-sq. ft. plots. Herbicides and rates included: Tenacity at 5.33 fl. oz./A tank-mixed with a nonionic surfactant at 0.25 percent v/v; Pylex at 1.33 fl. oz./A tank-mixed with a methylated seed oil at 0.5 percent v/v; Prograss 1.5 at 64 fl. oz./A; and a nontreated check for comparison (Table 1). We selected herbicides based on a combination of factors that included their safety for cool-season turfgrasses, control of perennial warm-season grasses, lack of zoysiagrass inclusion among tolerant turfgrasses on the herbicide label, and/or anecdotal evidence suggesting the herbicide may injure zoysiagrass.

Figure 2 Visible bleaching symptoms on zoysiagrass prior to winter dormancy from Tenacity (T) and Pylex (Py) applications. We observed little herbicide injury in the fall from Prograss (Pr) applications. The nontreated check (N) is shown for comparison. All labels are shown at the far-right edge of the plot. Photo taken Sept. 16, 2013 (two weeks after the initial application). (Photo: Aaron Patton)

Herbicides were applied starting in late August or early September each year, and each herbicide was applied three times at either a 2- or 3-week interval based on label recommendations (Table 1). We chose the application window in order to induce herbicide injury before the start of and during cold acclimation prior to winter, with the goal that a combination of herbicide and winter injury would control the zoysiagrass. We applied herbicides using a CO2 pressurized backpack sprayer equipped with XR8002 nozzle tips (Teejet, Spraying Systems Co., Wheaton, Ill.) calibrated to deliver 87 gallons/A at 30 psi.

We visually rated zoysiagrass injury (bleaching or phytotoxicity) in the fall at each application date, and visually assessed it on a 0-percent to 100-percent scale, where 0 percent was complete green tissue and 100 percent was completely bleached leaf tissue and/or a completely brown zoysiagrass plot. We also rated zoysiagrass green coverage on a 0-percent to 100-percent scale in June and July during the summer following applications. We converted data from percent coverage to percent control in each replication as {[1– (treatment coverage/coverage in nontreated plot)] × 100} prior to analysis. We analyzed all data using SAS, and means were separated using Fisher’s protected least significant difference (α=0.05).

Table 2 † Within columns, means followed by the same letter are not significantly different (∝=0.05). The nontreated check was excluded from the analysis. (Graph: Aaron Patton)

Herbicide effects on control

Our analysis revealed several instances where the treatments performed differently in each year, so zoysiagrass injury and control data from each year are presented separately. Three weeks after initial treatment, Pylex and Tenacity applications injured zoysiagrass more than Prograss (Figure 2), with the Pylex treatment providing 29-percent and 10-percent more injury than Tenacity in 2013 and 2015, respectively (Table 2). Injury was similar between Pylex and Tenacity applications in 2014 (Table 2). Subsequent injury ratings were consistent with those three weeks after initial treatment and are not shown for brevity. Zoysiagrass entered winter dormancy shortly after the last herbicide application each year (Table 1).

Figure 3 Herbicide and Application Year (Graph: Aaron Patton)

Zoysiagrass response to the previous year’s herbicide applications differed. In both 2013 and 2015, zoysiagrass control was highest from Pylex (equal to or greater than 46 percent) when measured in both June and July (Figure 3). In 2014, the response was similar between Pylex and Tenacity, but zoysiagrass control was less than 11 percent by July (Figure 3). It’s unclear why less Pylex control was observed in 2014. Application timings and the first day of freezing temperatures were similar in each year (Table 1). The average minimum air temperature during winter (December through March) was different for each year (2012-2013 = 15.1 degrees F, 2013-2014 = 19.3 degrees F, 2014-2015 = 28.5 degrees F) but did not help explain differences in the results. Although Tenacity caused about 49 percent or greater injury in all three years when rated three weeks after initial treatment (Table 2), it provided little to no zoysiagrass control (Figure 3). Prograss provided little to no zoysiagrass control in our study from fall applications. (Note: Anecdotal reports from superintendents suggest Prograss is more injurious to zoysiagrass when applied in spring, but we have yet to test this).

Pylex is labeled to control or suppress perennial warm-season grasses including common bermudagrass (Cynodon dactylon), dallisgrass (Paspalum dilatatum) and nimblewill (Muhlenbergia schreberi). Our study demonstrated that Pylex also provides zoysiagrass suppression, albeit inconsistent and incomplete control. Common bermudagrass control with Pylex is enhanced when coupled with overseeding of a cool-season turfgrass species. As such, late-summer and early fall Pylex applications followed by interseeding a cool-season turfgrass is our recommended strategy for zoysiagrass removal in cool-season turf.Aaron Patton, Ph.D., is a turfgrass scientist, and Daniel V. Weisenberger was a research associate (now retired) at Purdue University. You may reach Patton at ajpatton@purdue.edu for more information. The complete paper on which this article is based can be found at: Patton, A.J. and D.V. Weisenberger. 2017. Suppressing zoysiagrass (Zoysia japonica) in cool-season turf with topramezone. Crop, Forage, and Turf Management doi:10.2134/cftm2016.07.0052.

Acknowledgements
The authors want to express their gratitude to the Midwest Regional Turf Foundation for partial funding of this research.
References
Anonymous. 2013. Pylex herbicide label. BASF Corporation, 26 Davis Drive. Research Triangle Park, NC 27709.
Brosnan, J.T., and G.K. Breeden. 2013. Bermudagrass (Cynodon dactylon) control with topramezone and triclopyr. Weed Technol. 27(1):138-142.
Daniel, W.H. 1974. Turf Renovation with Glyphosate. Abstr. Annu. Meet Weed Sci. Soc. Am. p. 19.
Klingman, D.L. 1976. Killing Zoysia japonica ‘Meyer’ with herbicides. Proc. Ann. Meet. Northeastern Weed Sci. Soc. 30:344.
Patton, A.J., B.M. Schwartz, and K.E. Kenworthy. 2017. Zoysiagrass (Zoysia spp.) history, utilization, and improvement in the United States: A Review. Crop Science. 57:S-37–S-72. doi:10.2135/cropsci2017.02.0074

Table 1
† Treatments were applied with the same start date. Because of the shorter application interval for Tenacity, the last application was two weeks earlier than Prograss and Pylex.
‡ Oct. 23, 2013, Oct. 20, 2014 and Oct. 17, 2015 were the first autumn days with freezing temperatures recorded in West Lafayette, Ind. in each year, respectively, which signaled the end of the growing season, though zoysiagrass continued to maintain some green cover into November each year.
§ A nonionic surfactant at 0.25 percent v/v was tank-mixed with Tenacity and methylated seed oil at 0.5 percent v/v; was tank-mixed with Pylex. (Graph: Aaron Patton)