How Penoxsulam Delivers Precision Weed Control in Rice Cultivation

Introduction to Penoxsulam
Penoxsulam is a post-emergence herbicide primarily used in rice cultivation for controlling a broad range of grassy and broadleaf weeds. Belonging to the triazolopyrimidine sulfonamide chemical family, Penoxsulam is known for its high selectivity and effectiveness at low application rates. It plays a key role in modern weed management programs by reducing competition and improving crop yields.

Chemical Profile and Mode of Action
Penoxsulam has the chemical formula C₁₆H₁₄F₅N₅O₅S. It acts as an ALS (acetolactate synthase) inhibitor, classified under HRAC Group B. By blocking ALS enzyme activity, Penoxsulam disrupts the synthesis of branched-chain amino acids (valine, leucine, isoleucine), which are essential for cell division and plant growth. This causes gradual death of the weed while allowing crops like rice to remain unharmed.

Weed Control Spectrum
Penoxsulam is effective against a wide array of weeds including:

• Grassy weeds:Echinochloa spp., Leptochloa spp., Ischaemum rugosum

• Broadleaf weeds:Monochoria vaginalis, Ludwigia spp., Sphenoclea zeylanica

• Sedges:Cyperus difformis, Fimbristylis miliacea

Its broad-spectrum performance makes it suitable for both dry-seeded and transplanted rice systems.

Advantages of Using Penoxsulam

• Low use rates: Effective at doses as low as 15–25 g a.i./ha

• Crop safety: High selectivity toward rice crops

• Environmental compatibility: Low toxicity to birds, mammals, and aquatic life under proper use

• Flexible timing: Can be applied early or late post-emergence depending on weed pressure

• Compatibility: Can be tank-mixed with other herbicides for resistance management or broadened spectrum

Application Guidelines
Penoxsulam is typically applied as a foliar spray, often formulated as an OD (oil dispersion) for improved efficacy and uptake. For best results, apply when target weeds are in the early growth stages (2–4 leaf stage). Good soil moisture and coverage are crucial for optimal absorption.

Environmental and Safety Considerations
Penoxsulam is considered to have low mammalian toxicity and minimal risk to non-target organisms when applied correctly. However, it can persist in water for several days, so care should be taken near aquatic environments. Avoid runoff or direct application into water bodies.

Resistance Management
Although Penoxsulam is currently effective, over-reliance on ALS inhibitors can lead to resistance. To mitigate this risk:

• Rotate with herbicides of different modes of action

• Integrate non-chemical weed control methods

• Avoid repeated use in the same field season

FAQ About Penoxsulam

Q1: What crops can Penoxsulam be used on?
Primarily used on rice, though some regulatory frameworks allow for use in other cereals or turfgrass in certain countries.

Q2: When should Penoxsulam be applied?
Apply post-emergence when weeds are actively growing and before they become well-established.

Q3: Is Penoxsulam safe for aquatic environments?
It is low in aquatic toxicity but should not be applied directly to water or near field drainage ditches unless approved.

Q4: Can it be mixed with other herbicides?
Yes, Penoxsulam is often tank-mixed with other herbicides like cyhalofop or bispyribac-sodium for enhanced control and resistance management.

Q5: Is resistance a concern with Penoxsulam?
Yes, as with all ALS inhibitors. Proper rotation and integrated weed management practices are recommended.