Penoxsulam: A Broad-Spectrum Post-Emergent Herbicide

Definition:
Penoxsulam is a post-emergent, systemic herbicide widely used for controlling broadleaf, sedge, and grassy weeds in rice cultivation, turfgrass management, and aquatic weed control. It belongs to the triazolopyrimidine sulfonamide chemical family and is known for its high selectivity and low application rates.

Chemical Characteristics of Penoxsulam:

• Chemical Name: 2-(2,2-Difluoroethoxy)-N-(5,8-dimethoxy[1,2,4]triazolo[1,5-c]pyrimidin-2-yl)-6-(trifluoromethyl)benzenesulfonamide

• Molecular Formula: C₁₆H₁₄F₅N₅O₅S

• Molecular Weight: 483.4 g/mol

• Appearance: Off-white crystalline solid.

• Solubility: Low solubility in water; soluble in organic solvents.

• Stability: Stable under normal storage and pH conditions; hydrolyzes slowly in alkaline environments.

Mode of Action:

Penoxsulam inhibits acetolactate synthase (ALS), an enzyme crucial for the biosynthesis of branched-chain amino acids in plants. This leads to disruption of protein synthesis, cessation of growth, and eventual death of susceptible weeds.

Uses and Applications:

1. Target Weeds:

   • Broadleaf weeds: Ludwigia spp., Ammannia spp., Monochoria spp.

   • Grasses: Echinochloa spp. (barnyardgrass)

   • Sedges: Cyperus difformis, Fimbristylis spp.

2. Crops and Areas of Use:

   • Paddy rice (direct-seeded and transplanted).

   • Turfgrass management (e.g., golf courses, lawns).

   • Aquatic weed control in ponds and irrigation canals.

3. Timing:

   • Post-emergence: Apply when weeds are young and actively growing.

Benefits of Penoxsulam:

• Broad Spectrum: Controls grasses, sedges, and broadleaf weeds in one application.

• Highly Selective: Safe for rice and turfgrass when used at labeled rates.

• Low Use Rate: Effective at low application doses, reducing chemical load.

• Flexible Application: Works in both flooded and non-flooded conditions for rice.

Limitations:

• Weed Size Sensitivity: Best results on small, actively growing weeds.

• Resistance Risk: Overuse may lead to ALS inhibitor resistance in weeds.

• Slow Activity: Weed death may take 2–4 weeks after application.

Recommended Application:

• Dosage: Typically 15–25 g active ingredient per hectare in rice; rates vary by region and weed pressure.

• Method: Foliar spray using flat fan nozzles for uniform coverage.

• Precautions:

  • Ensure weeds are young for optimum control.

  • Rotate herbicides with different modes of action.

  • Avoid drift to non-target plants, especially broadleaf crops.

Storage and Handling:

• Storage: Keep in tightly closed containers in a dry, cool area.

• Shelf Life: Generally stable for 2–3 years under recommended storage.

• Safety: Non-volatile but avoid inhalation and direct contact; toxic to some aquatic organisms.

FAQ on Penoxsulam:

Q1: What is Penoxsulam mainly used for?
A1: It is primarily used for post-emergent weed control in rice fields, turfgrass, and aquatic systems.

Q2: How fast does Penoxsulam work?
A2: Initial weed symptoms appear in 5–7 days, with full control achieved in 2–4 weeks.

Q3: Is Penoxsulam safe for rice crops?
A3: Yes, it is highly selective to rice when used at recommended rates.

Q4: How can resistance be managed?
A4: Use in rotation or mixtures with herbicides of different modes of action and practice integrated weed management.