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Research UPDATE – Influence of Herbicide Combinations and Sequential Applications on Windmillgrass (Chloris verticillata) Control

(By Nic Mitchell and Jared Hoyle, KSU Turfgrass Research and Extension)

Windmillgrass (Chloris verticillata Nutt.) populations commonly infest turfgrass systems in the mid-west, which result in aesthetically unacceptable turfgrass stands. Windmillgrass is a perennial monocot bunch-type grass. It often spreads by stolons and by its panicle shape seed which acts much like tumble weed.

Prior research found that Pylex (topramezone) and Acclaim Extra (fenoxaprop) result in fair to minimal control of windmillgrass with a single application. Tenacity (mesotrione) which, labeled for two applications for best control of windmillgrass, recommends the second application should be three weeks after initial application. Additionally, studies have shown the addition of triclopyr to HPPD inhibitor herbicides increases windmillgrass control in a controlled environment.

The goal of this research was to determine the effect of a sequential postemergent herbicide applications and the addition of triclopyr to HPPD inhibitors herbicides on windmillgrass control.

Research trials were initiated in 2018 at Rocky Ford Turfgrass Research Center in Manhattan, Kansas. Windmillgrass was infested in a low maintenance tall fescue (Schedonorus arundinaceus) system. Seven herbicide combinations were applied as a single application or with a sequential application and non-treated control was included for comparison for a total of 15 individual treatments. All herbicide treatments were applied on August 16, 2018 and treatments that received a sequential application were applied on September 9, 2018. Herbicide treatments consisted of Pylex (topramezone) at 2 fl oz/a, Tenacity (mesotrione) at 8 fl oz/a, Acclaim (fenoxaprop) at 39 fl oz/a, Alligare Triclopyr 4 (triclopyr) at 32 fl oz/a, Pylex (topramezone) at 2 fl oz/a + Alligare Triclopyr 4 (triclopyr) at 32 fl oz/a, Tenacity (mesotrione) at 8 fl oz/a + Alligare Triclopyr 4 (triclopyr) at 32 fl oz/a, Acclaim (fenoxaprop) at 39 fl oz/a + Alligare Triclopyr 4 (triclopyr) at 32 fl oz/a, and a nontreated control. Data collection consisted of visual percent windmillgrass cover (0-100%) and were transformed to percent windmillgrass control for presentation purposes. Analysis of variance (ANOVA) was performed in SAS 9.4 (SAS Institute Inc., Cary, NC) and means were separated according to Fisher’s protected least significant difference (LSD) level at 0.05.

We found that Pylex (topramezone) applied at 2 fl oz/a resulted in 87% windmillgrass control at 8 weeks after treatment. A single application of Pylex (topramezone) at 2 fl oz/a + Alligare Triclopyr 4 (triclopyr) at 32 fl oz/a and Tenacity (mesotrione) at 8 fl oz/a + Alligare Triclopyr 4 (triclopyr) at 32 fl oz/a resulted in 96% and 97% windmillgrass control 8 weeks after initial treatment, respectively. All treatments that received a sequential application on September 9, 2018 excluding the non-treated control and Acclaim (fenoxaprop) at 39 fl oz/a provided 100% windmillgrass control at 8 WAT. Acclaim (fenoxaprop) at 39 fl oz/a applied on August 16, 2018 followed by an application at 39 fl oz/a on September 9, 2018 resulted in 88% windmillgrass control.

Table 1. Windmillgrass (Chloris verticillata Nutt.) control 8 weeks after initial application from single and sequential applications at Rocky Ford Turfgrass Research Center in Manhattan, KS; 2018.

Treatment Herbicide Rate Application Date Controla
___%___
1 non-treatedb 4 Cc
2 Pylex + MSOd 2 fl oz/a + 1% v/v Aug. 16, 2018 87 A
3 Tenacity + NISd 8 fl oz/a + 0.25% v/v Aug. 16, 2018 9 C
4 Acclaim Extra + NIS 39 fl oz/a + 32 fl oz/100 gal Aug. 16, 2018 16 C
5 Triclopyr 32 fl oz/a Aug. 16, 2018 64 B
6 Pylex + Triclopyr + MSO 2 fl oz/a + 32 fl oz/a + 1% v/v Aug. 16, 2018 96 A
7 Tenacity + Triclopyr +NIS 8 fl oz/a + 32 fl oz/a + 0.25% v/v Aug. 16, 2018 97 A
8 Acclaim Extra + Triclopyr +NIS 39 fl oz/a + 32 fl oz/a + 32 fl oz/100 gal Aug. 16, 2018 63 B
9 Pylex + MSO 2 fl oz/a + 1% v/v Aug. 16, 2018 fbe Sept. 9, 2018 100 A
10 Tenacity + NIS 8 fl oz/a + 0.25% v/v Aug. 16, 2018 fb Sept. 9, 2018 100 A
11 Acclaim Extra + NIS 39 fl oz/a + 32 fl oz/100 gal Aug. 16, 2018 fb Sept. 9, 2018 88 A
12 Triclopyr 32 fl oz/a Aug. 16, 2018 fb Sept. 9, 2018 100 A
13 Pylex + Triclopyr + MSO 2 fl oz/a + 32 fl oz/a + 1% v/v Aug. 16, 2018 fb Sept. 9, 2018 100 A
14 Tenacity + Triclopyr +NIS 8 fl oz/a + 32 fl oz/a + 0.25% v/v Aug. 16, 2018 fb Sept. 9, 2018 100 A
15 Acclaim Extra + Triclopyr +NIS 39 fl oz/a + 32 fl oz/a + 32 fl oz/100 gal Aug. 16, 2018 fb Sept. 9, 2018 100 A

a Ratings were conducted 8 weeks after initial application; October 11, 2018.

b Non-treated control contained approximately 65% windmillgrass cover throughout the research trial. 4% control was observed due natural declining of windmillgrass populations to environmental considerations on October 11, 2018.

c Treatment means followed by a common capital letter are not significantly different according to Fisher’s protected LSD (α= 0.05).

d MSO, methylated seed oil and NIS, non-ionic surfactant were added to treatments according to herbicide manufacture recommendations.

e fb, followed by.


Always remember to READ THE LABEL for the correct rate, turfgrass tolerance, and specific instructions before application!!!

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