Pyrithiobac Sodium 10 EC: Post-Emergence Cotton Weed Care

Chemical Class and ALS Enzyme Inhibition

Pyrithiobac Sodium belongs to the pyrimidinyl carboxy chemical class (HRAC Group 2 - ALS inhibitors). It functions by inhibiting the plant enzyme acetolactate synthase (also known as acetohydroxyacid synthase / AHAS).

This enzymatic inhibition shuts down the biosynthesis of critical branched-chain amino acids (valine, leucine, and isoleucine). Susceptible broadleaf weeds stop growing within hours of foliar absorption, developing chlorotic growing points followed by complete necrosis over 7 to 14 days.

• HRAC Group 2 Mode of Action: Blocks branched-chain amino acid synthesis in target weed seedlings.
• High Cotton Crop Selectivity: Cotton plants rapidly detoxify the herbicide through metabolic degradation.
• Emulsifiable Concentrate (10% EC): High-solubility formulation providing rapid leaf cuticle penetration.

Target Broadleaf Weed Spectrum in Cotton

Broadleaf weed competition during early vegetative stages can severely stunt cotton seedlings and reduce boll formation. Pyrithiobac Sodium 10% EC targets stubborn taprooted annual and perennial broadleaf weeds.

Key controlled broadleaf species include Trianthema portulacastrum (horse purslane / itsit / carpetweed), Digera arvensis, Amaranthus viridis, Celosia argentea, and Corchorus trilocularis, eliminating labor-intensive manual weeding.

• Carpetweed Control: Outstanding control over aggressive Trianthema portulacastrum flushes.
• Broadleaf Suppression: Controls Amaranthus, Digera, and Celosia competing for root nutrients.
• Selective Over-the-Top Application: Can be sprayed safely over growing cotton plants when weeds are young.

Application Timing and Spray Guidelines

Apply Pyrithiobac Sodium 10% EC as an early post-emergence spray when target broadleaf weeds are at the 2 to 4 leaf stage (typically 20 to 30 days after cotton sowing). Ensure adequate soil moisture is present during application.

Use a knapsack or tractor-mounted boom sprayer fitted with flat fan nozzles to achieve uniform foliar coverage. Avoid spraying during drought stress or when cotton plants are stressed by severe waterlogging.

• Optimal Weed Stage: Spray when weed seedlings are actively growing at 2 to 4 leaves.
• Soil Moisture Requirement: Adequate root zone moisture ensures vigorous weed uptake and rapid systemic translocation.
• Nozzle Selection: Use flat fan nozzles to produce even droplet distribution across cotton inter-rows.

Related on KisanPe

• Cotton Farmer Solutions →
• Crop Protection Advisory →
• Soil Health Management →
• Pesticide calculator →
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Common questions

General guidance, not personal advice. For your farm, ask your local Krishi Vigyan Kendra or agriculture officer.