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Imazapyr Herbicides

Imazapyr was registered with the EPA for aquatic use in 2003. The active ingredient is isopropylamine salt of imazapyr, (2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-3-pyridinecarboxylic acid). Formulations that can be used on aquatic vegetation include Habitat™, Ecomazapyr 2sl™, Imazapyr 2sl™, and Polaris AC. Imazapyr is used for control of emergent and floating-leaf vegetation. Imazapyr is not recommended for control of submersed vegetation.

Aquatic Use and Considerations

Imazapyr is a systemic herbicide that moves throughout the plant tissue and prevents plants from producing a necessary enzyme, acetolactate synthase (ALS), which is not found in animals. Susceptible plants will stop growing soon after treatment and become reddish at the tips of the plant. Plant death and decomposition will occur gradually over several weeks to months. Imazapyr should be applied to plants that are actively growing. If applied to mature plants, a higher concentration of herbicide and a longer contact time will be required.

Imazapyr is used to control the invasive plants common reed (Phragmites australis), purple loosestrife (Lythrum salicaria) and Japanese knotweed (Polygonum cuspidatum). Native species that are also controlled include cattails (Typha spp.), water lilies (Nymphaea sp.), pickerelweed (Pontederia cordata), duckweeds (Lemna spp.) and arrowhead (Sagittaria spp.).

It is important to note that repeated use of herbicides with the same mode of action can lead to herbicide-resistant plants, even in aquatic plants. More resistant weeds have developed to the ALS inhibitor herbicides than to other herbicide types, and so this mechanism of action may be more susceptible to developing resistance. In order to prevent herbicide resistance, avoid using the same type of herbicides year after year, and when possible, use non-herbicide methods of control instead.

Shoreline Knowledge Base Biology and Control of Aquatic Plants

Biology and Control of Aquatic Plants 
Imazapyr Chemical Fact Sheet

Note: Products may not be registered for use in your state or locale. Check to be sure a specific use pattern is approved in your area before use. Check product labeling or your local state agency for more information. Most current product labels are available by visiting the product manufacturers website or at https://www.cdms.net

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Arsenal AC Applicators Concentrate Herbicide, BASF

Arsenal AC Applicator's Concentrate Herbicide, when it comes to controlling unwanted brush, traditional mechanical methods don't really cut it. Re-sprouts and increased stem densities lead to more mowing – and more costs.

Active Ingredient: Isopropylamine Salt of Imazapyr 53.1%

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Habitat Aquatic Herbicide, SePRO

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Active Ingredient: Ispropylamine salt of Imazapyr 27.77%

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Polaris Herbicide, Nufarm

Nufarm Polaris is a liquid post-emergent herbicide that contains Imazapyr for effective management of grasses and broadleaf weeds, undesirable emergent and floating aquatic vegetation, and many brush and vine species in a variety of settings. Nufarm Polaris provides a multi-purpose label that includes vegetation management, aquatic and railroad applications.

Active Ingredients : Imazapyr 27.7%

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