New Herbicides for 2021, Part I

By Scott McElroy, Ph.D. – Professor, Department of Crop, Soil, and Environmental Sciences Jim Harris – Research Associate, Department of Crop, Soil, and Environmental Sciences, Auburn University

The following article will discuss select new products that will be available for turfgrass industry use in 2021. The discussion of these products is not an endorsement of the products and exclusion of products that may be newly available is not opposition to those products. Products discussed have been researched in Dr. McElroy’s research group and some available data is presented. Always follow the label regardless of what any article may say about a product. The label is the law.

New herbicide products do not necessarily mean new active ingredients. New herbicide product names may simply be repackaged active ingredients or novel mixtures of previously available active ingredients. Novel active ingredients are a rarity with respect to new herbicide products. The lack of a novel active ingredient does not necessarily mean that the products do not bring a new control angle to the turfgrass industry. Novel combinations of older active ingredients can provide additive or even synergistic herbicide effects and can broaden the spectrum of weeds controlled. But with new combinations it is important to understand the activity of individual active ingredients contained in the products.

Coastal

Coastal herbicide is a new combination of older products – imazaquin, prodiamine, and simazine. Imazaquin previously labeled as Image can now be purchased as the stand alone product Scepter T&O. Prodiamine was first labeled as Barricade and simazine was first labeled as Princep (There are other product names, it is simply easier to refer to the first product name used).

New herbicide mixtures primarily target new combinations of post herbicides — Trimec-type herbicides or herbicides with mixtures of sulfentrazone (Dismiss) and quinclorac (Drive). Echelon is a combination of prodiamine and sulfentrazone, pre and post, respectively, but few (if any) others exist. Coastal is another unique combination because it also combines both pre and post herbicides. Prodiamine is strictly a preemergence herbicide with no postemergence activity. Simazine is used for post winter weed control, primarily Poa annua, but it can provide 14–28 days of residual. Imazaquin is a postemergence herbicide with minimal residual activity.

Coastal is labeled for use on bermudagrass, centipedegrass, St. Augustinegrass, and zoysiagrass. Like the name implies, it is primarily targeted at warm-season turf along the gulf coast. Being registered for weed control on the four-primary warmseason grasses is important for lawn care because it does not require the changing of products from one turfgrass lawn to the next.

Research conducted in 2019–2020 evaluated Coastal in September and October for Poa annua and winter annual broadleaf control. Coastal was applied at 32 or 64 fl oz/a with or without metsulfuron (MSM) at 0.5 oz/a. A comparison treatment Specticle at 6.5 fl oz/a plus metsulfuron at 0.5 fl oz/a was included.

• All treatments controlled Poa annua completely regardless of split or single applications (data not shown). The additional benefit of Coastal is that it also provided effective control of the annual broadleaf, small hop clover (Trifolium dubium; Figure 1). Coastal with and without metsulfuron reduced hop clover cover to 2–4%, while hop clover cover was > 25% in non-treated plots. The combination of residual activity from prodiamine and simazine combined with the postemergence activity of simazine and imazaquin likely lead to the effective control.

FIGURE 1: Small hop clover control with Coastal.

Vexis

Vexis is a new herbicide product containing the new active ingredient pyrimisulfan. It is a sedge control herbicide with excellent cool and warm-season turfgrass safety. It is also labeled for golf and residential turf. Vexis is currently only sold as a granular. A sprayable formulation is currently in the registration pipeline.

There are many herbicide options for sedge control in turf. Twenty to 30 years ago, herbicides for sedge control in turfgrass were primarily limited to MSMA and Basagran (bentazon). Now, several ALS-inhibitors are available including Sedgehammer (halosulfuron), Monument (trifloxysulfuron), Certainty (sulfosulfuron), Celero (imazosulfuron), and Katana (flazasulfuron). Also, Dismiss (sulfentrazone) is a PPO-inhibitor that provides a different mode of action for sedge control in cases of herbicide resistance.

Vexis is an ALS inhibiting herbicide, so it does not bring a new mode of action to the table for sedge control. The current benefits of Vexis are that it can be applied as a granular and with a high level of cool and warm-season turfgrass safety. Safety across cool and warm-season turfgrass is beneficial for the transition zone where such grasses may be directly adjacent to each other. Expect new herbicides in the future that use pyrimisulfan in a novel mixture to gain a greater spectrum of weed control.

Scepter T&O

Imazaquin was first used in turfgrass under the trade name of Image. Since then, the “Image” name has been re-branded for the home lawn care market and an Image branded product can contain atrazine, MSMA (in the past), or other active ingredients. Image is less of a herbicide brand name and more of a marketing strategy for herbicide products in the consumer herbicide space.

Scepter T&O has replaced Image as the standalone product containing only imazaquin. There is nothing new about Scepter T&O, only the name has changed. Imazaquin is a unique, probably overlooked product. As products age, marketing budgets do not keep up and consumers are attracted to the newer, flashier products. Newer products are not necessarily better, but they can highlight some of the issues with an older active ingredient.

Imazaquin is one of those active ingredients that was exposed with the introduction of new products. While it has sedge, broadleaf, and cool season grass activity, one of the needs of newer products is broad spectrum activity and excellent turfgrass safety. Imazaquin is effective for sedge control, but it really needs a tank-mix partner like MSMA for consistent effectiveness. It is not broad spectrum for broadleaf weed control either and Poa annua control can be inconsistent.

Research was conducted in 2019 to evaluate combinations of Scepter T&O for doveweed control. Treatments included Scepter 5.7 oz/a plus Dismiss 4.0 fl oz/a applied three times (24 June, 16 July, 5 August), Scepter 8.5 oz/a plus Dismiss 6.0 fl oz/a applied two times (24 June, 16 July), Scepter T&O at 8.6 oz/a plus metsulfuron at 0.5 oz/a applied two times (24 June, 16 July), and Celsius at 4.9 oz/a applied twice (24 June and 16 July). All treatments contained non-ionic surfactant and were applied at 30 gallons per acre spray volume.

Doveweed plot cover was approximately 20 to 30% at the time of application on 24 June (Figure 2). Following sequential applications, all treatments reduced doveweed cover to 0 to 3% cover two weeks after the second applications. Three applications of Scepter plus Dismiss at a lower rate was not more effective when rated on 13 September than two applications at a higher rate (Figure 3). All treatments were statistically equivalent in doveweed plot cover (2–6%) as rated on 13 September while non-treated plots had approximately 80% plot cover. Based on past research and observations, all treatments provided excellent doveweed control.

FIGURE 2

Final Thoughts

This article is meant to highlight a select set of new herbicides entering the turfgrass market. Expect follow up articles this year discussing other new products.

FIGURE 3 A – Non-Treated

August 9, 2019 – 4 Days After C Application

FIGURE 3 B – Scepter 5.7 oz/a + Dismiss 4.0 oz/a ABC

August 9, 2019 – 4 Days After C Application