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Pursuit / imazethapyr

Chemical Structure

Chemical Name:

2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-5-ethyl-3-pyridinecarboxylic acid.

Chemical Family:


WSSA Resistance Group:


Crop/non-crop registration:

Soybeans, beans, imidazolinone-resistant (IR) corn, alfalfa for seed

Sensitive weeds:

Many annual BLW (broadleaf weeds) species and several annual grasses, especially when applied PPI, PRE, or early POST (2-leaf stage of weeds): green and yellow foxtails, barnyardgrass, witchgrass, cocklebur, velvetleaf, common ragweed, wild mustard, redroot pigweed, lambsquarters, smartweed.

Application method:


Absorption & Translocation:

Readily absorbed by foliage;root absorption also occurs but is slower; translocated via both the xylem and phloem.

Mode of Action:

Inhibition of acetolactate synthase.

Metabolic pathway inhibited:

Inhibits acetolactate synthase (ALS), also called acetohydroxyacid synthase (AHAS), a key enzyme in the biosynthesis of the branched-chain amino acids isoleucine, lecucine, and valine.

Basis of Selectivity:

Metabolized by tolerant species to non-phytotoxic compounds.


Growth of treated plants is inhibited within a few hours after application and susceptible weeds are no longer competitive with the crop; injury symptoms usually appear 1-2 wks after application; following growth inhibition, meristematic areas gradually become chlorotic and necrotic, and this is followed by a slow general foliar chlorosis and necrosis.


Intermediate-long (4-6 months) depending on weather and soil conditions (more persistent under dry conditions); see additional comments section below.


Oral LD50 = >5000 mg/kg - practically non-toxic (PURSUIT = >5000 mg/kg - practically non-toxic).

Additional comments:

Rotational cropping restricted to soybeans, white and kidney beans, processing peas, corn, spring barley, spring wheat, and winter wheat (but for this latter crop, a period of 100 days is required between application of imazethapyr and planting); do not plant other crops the year following application as injury may result; can be applied up to 30 days prior to planting; can be used in reduced and no-till situations; POST applications require the addition of a surfactant and liquid fertilizer solution for maximum efficacy; temporary soybean discoloration and/or stunting may occur with POST applications.