The Lowdown on Herbicides

Always Read the Label Before Applying Herbicides

There are currently 19 families of herbicides and thousands of different formulations and brand names available, which can make deciding which product to use seem daunting. To help streamline the process, TCWP only carries products that treat species listed on the State Designated and County Declared Lists.

Basic Classification of Herbicides

Auxin Mimic Herbicides

Chemical Names: Aminopyralid (Milestone & Opensight), 2,4-D (Speedzone & Weedmaster/Rangestar), & Dicamba (Speedzone & Weedmaster/Rangestar)Common Use Names/Product Names: Milestone, Opensight, Speedzone, Weedmaster, or RangeStar (read on for specific uses for each brand)Mode of Action & Best Uses: Auxin Mimic Herbicides work particularly well on herbaceous, broadleaf plant species, and have limited control of some annual grasses. They cause the plant to undergo rapid, uncontrolled growth, which eventually kills the plant.Milestone and Opensight can be used in noncrop, natural areas, and rangeland. They provide residual control for germinating seeds. These products should not be used within the drip line of conifers, or to vegetation that may be composted, or used on desirable vegetation.Speedzone does not provide residual control that Milestone and Opensight provides, but it is a good alternative for treatments in lawns. WeedMaster - In instances when grass hay will be used on desirable vegetation, Weedmaster provide control of broadleaf species without impacting desirable vegetation through hay or manure.

ALS inhibitors

Chemical Names: chlorsulfuron (Telar), metsulfuron-methyl (Escort & Opensight), rimsulfuron (Laramie), and imazapic (Plateau)Mode of Action & Best Uses:  Inhibit branch chain amino-acid synthesis or acetolactate synthase (ALS) inhibiting herbicides, also referred to as acetohydroxyacid synthase (AHAS). Controls many broadleaf species, some grass species, and some shrubby species. Not for use in lawns.

Sulfonylureas

Telar (Chlorsulfuron)Best Uses:  Best for most of TCWP listed species because it is very effective and less harsh on non-target plants than Escort – toadflax, hoary alyssum, field bindweed, houndstongue, common mulleinEscort & Opensight (Metsulfuron-methyl)Best Uses: Works well on most TCWP listed species, but can have more non-target damage on desirable grasses and shrubby species (such as willow and sage).Laramie (Rimsulfuron)Mode of Action: Cheatgrass control – in September/October this can be used as a replacement for Telar in a tank mix with Milestone to control more listed species when also treating cheatgrass.

Imidazolinones

Plateau (Imazapic)Mode of Action & Best Uses: Much less selective that the other listed herbicides. Controls cheatgrass, but also impacts non-target grasses, forbs, and potentially trees if applied incorrectly.

EPSP Synthase Inhibitors

Chemical Name: glyphosate (Roundup)Mode of Action & Best Uses:  Inhibit branch chain amino-acid synthesis or acetolactate synthase (ALS) inhibiting herbicides, also referred to as acetohydroxyacid synthase (AHAS). Controls many broadleaf species, some grass species, and some shrubby species. Not for use in lawns.Roundup (Glyphosate)Mode of Action & Best Uses: Inhibits 5-enolpyruvylshikimate-3-phosphate (EPSP) synthase which is needed for protein systhesis. A non-selective herbicide. Excellent for “bareground” control (eg driveways and walkways). Can be used under the dripline of trees to treat invasive species without impacting the tree.Diving into the world of herbicides can be a bit overwhelming, but that is what TCWP is here for. For advice on controlling invasive species, herbicide questions, or for a free consultation of your Teton County residence, please contact Teton County Weed & Pest District at 307-733-8419.