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

Windmillgrass (Chloris verticillata Nutt.) populations commonly infest turfgrass systems in the midwest, which result in aesthetically unacceptable turfgrass stands. Pylex (topramezone) and Acclaim Extra (fenoxaprop) have resulted in fair control of windmillgrass with single applications. For adequate control of windmillgrass, a sequential application of Tenacity (mesotrione), three weeks after the initial application, is recommended. Additionally, studies have shown the addition of triclopyr to HPPD inhibitor herbicides increases windmillgrass control in a controlled environment. Field experiments were initiated in 2018, at the Kansas State University Rocky Ford Turfgrass Research Center in Manhattan, KS, to determine the influence of herbicide combinations with the addition of triclopyr and sequential applications on windmillgrass control.


Influence of Herbicide Combinations and Sequential Applications on Windmillgrass (Chloris verticillata) Control
Nicholas Mitchell and Jared Hoyle Summary Windmillgrass (Chloris verticillata Nutt.) populations commonly infest turfgrass systems in the midwest, which result in aesthetically unacceptable turfgrass stands. Pylex (topramezone) and Acclaim Extra (fenoxaprop) have resulted in fair control of windmillgrass with single applications. For adequate control of windmillgrass, a sequential application of Tenacity (mesotrione), three weeks after the initial application, is recommended. Additionally, studies have shown the addition of triclopyr to HPPD inhibitor herbicides increases windmillgrass control in a controlled environment. Field experiments were initiated in 2018, at the Kansas State University Rocky Ford Turfgrass Research Center in Manhattan, KS, to determine the influence of herbicide combinations with the addition of triclopyr and sequential applications on windmillgrass control.

Rationale
Windmillgrass is a problematic perennial grassy weed commonly found in established turfgrass in the midwest. Currently, mesotrione and topramezone (4-hydroxyphenylpyruvate dioxygenase [HPPD] inhibitor) are the only available labeled post-emergent active ingredients available for windmillgrass control in turfgrass systems.

Objective
The objective of this study was to determine the effect of sequential postemergent herbicide applications and the addition of triclopyr to HPPD inhibitor herbicides on windmillgrass control.

Study Description
Research trials were initiated in 2018 at Rocky Ford Turfgrass Research Center in Manhattan, KS. Windmillgrass (Chloris verticillata Nutt.) populations consisted of 65% cover in a low maintenance tall fescue (Schedonorus arundinaceus) system. Throughout the research, trial plots were maintained at 3 inches and no supplemental irrigation was applied. Treatments were arranged in a randomized complete block design with 4 replications. Seven herbicide combinations were applied as a single application or with a sequential application, and a 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. A surfactant was added to each herbicide treatment according to the manufacturer's directions. Herbicide treatments were applied using a CO 2 pressurized backpack boom sprayer calibrated to deliver 43.56 GPA at 37 psi. Data collected for research trials consisted of visual percent windmillgrass cover (0-100%) and were transformed to percent windmillgrass control for presentation purposes. Evaluations were conducted weekly for 8 weeks after the initial application. 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.

Kansas State University Agricultural Experiment Station and Cooperative Extension Service
Brand names appearing in this publication are for product identification purposes only. No endorsement is intended, nor is criticism implied of similar products not mentioned. Persons using such products assume responsibility for their use in accordance with current label directions of the manufacturer. Non-treated control contained approximately 65% windmillgrass cover throughout the research trial. Only 4% control was observed on October 11, 2018, due to natural declining of windmillgrass populations because of environmental conditions. c Treatment means followed by a common capital letter are not significantly different according to Fisher's protected LSD (α= 0.05). d Methylated seed oil (MSO) and non-ionic surfactant (NIS) were added to treatments according to herbicide manufacture's recommendations. e fb = followed by.