Penoxsulam: A Modern Herbicide for Rice Weed Management

Technical Introduction

Penoxsulam (IUPAC: 2-(2,2-difluoroethoxy)-6-(trifluoromethyl)-N-(5,8-dimethoxy[1,2,4]triazolo[1,5-c]pyrimidin-2-yl)-benzenesulfonamide) is a systemic, post-emergence herbicide belonging to the triazolopyrimidine sulfonamide class.

It works by inhibiting acetolactate synthase (ALS/AHAS), an enzyme essential for the biosynthesis of branched-chain amino acids (valine, leucine, and isoleucine). This leads to growth inhibition and eventual death of susceptible weeds.

• Mode of Action: ALS inhibitor (HRAC Group B).

• Systemicity: Rapidly absorbed by foliage and roots, translocated throughout the plant.

• Selectivity: Specifically designed for rice (both transplanted and direct-seeded).

Applications

• Primary Crop:

  • Rice (both paddy and direct-seeded systems).

• Target Weeds:

  • Controls a wide spectrum of annual grasses, sedges, and broadleaf weeds, including:

    • Echinochloa crus-galli (barnyardgrass)

    • Fimbristylis miliacea (sedge)

    • Cyperus difformis (smallflower umbrella sedge)

    • Monochoria vaginalis (pickerelweed)

    • Ludwigia spp. (water primrose)

• Timing:

  • Applied early post-emergence when weeds are young and actively growing.

• Formulation Use:

  • Available as OD (oil dispersion) or SC (suspension concentrate).

Advantages

• Broad Spectrum: Controls grasses, sedges, and broadleaves with a single application.

• Crop Safety: Selective for rice at recommended doses.

• Low Use Rate: Effective at very low dosages compared to older herbicides.

• Environmental Benefits: Lower application volume reduces chemical load in the field.

• Resistance Management Tool: Alternative to ACCase inhibitors and synthetic auxins in rice.

Specifications (Typical Parameters)

FAQ

Q1: What is Penoxsulam mainly used for?
A: It is primarily used in rice cultivation to control grasses, sedges, and broadleaf weeds.

Q2: How is Penoxsulam applied?
A: Typically applied as a post-emergence foliar spray when weeds are in their early growth stages.

Q3: Does Penoxsulam have residual activity?
A: Yes, it provides 2–4 weeks of residual control, depending on soil type and water management.

Q4: Can Penoxsulam be tank-mixed with other herbicides?
A: Yes, it is often mixed with bispyribac-sodium, pyrazosulfuron-ethyl, or butachlor to broaden the weed control spectrum and manage resistance.

Q5: What is the typical application rate?
A: Generally 15–40 g a.i./ha, depending on crop stage, weed density, and formulation.

Q6: Is Penoxsulam safe for the environment?
A: It is considered environmentally favorable due to low use rates, but caution is advised in aquatic ecosystems.