Imidazolinones

Imidazolinones are a class of synthetic herbicides that belong to the imidazolinone chemical family. They act as inhibitors of acetolactate synthase (ALS), the enzyme responsible for the first step in the biosynthesis of the branched-chain amino acids valine, leucine, and isoleucine. By blocking this pathway, imidazolinones disrupt plant growth and cause death in susceptible species. They are systemic and can be absorbed through roots or foliage and translocated within the plant.

Common members include imazapyr, imazethapyr, imazamox, imazaquin, and imazapic. These herbicides control a range of annual grasses and broadleaf weeds and are widely used in crops where ALS-tolerant varieties or crops with tolerance to imidazolinones are grown. They can be applied pre- or post-emergence depending on the product and the target weeds, with selectivity arising from crop tolerance or from specific mitigation strategies.

Resistance management is a consideration with this class, as weeds can evolve resistance to ALS inhibitors through target-site mutations or other mechanisms. Cross-resistance can occur among ALS-inhibiting herbicides, so integrated weed management and rotation with herbicides of different modes of action are advised to sustain effectiveness.

Environmental and safety notes indicate that persistence and mobility vary by compound and environmental conditions. Imidazolinones generally have moderate mammalian toxicity, but risk depends on exposure, formulation, and application practices. Regulatory status and usage restrictions vary by country, with labeling specifying rates, timing, and environmental safeguards.