Paraquat Aqueous: A Fast-Acting Non-Selective Herbicide

Definition:
Paraquat aqueous is a non-selective, contact herbicide used to control a wide range of annual and perennial weeds. It is formulated as a water-based (aqueous) solution and is known for its rapid desiccation effect on green plant tissues. Paraquat is widely used in agriculture for pre-plant burndown, inter-row weed control, and non-crop areas.

Chemical Characteristics of Paraquat Aqueous:

• Chemical Name: 1,1′-dimethyl-4,4′-bipyridinium dichloride

• Molecular Formula: C₁₂H₁₄Cl₂N₂

• Molecular Weight: 257.16 g/mol

• Appearance: Dark blue-green aqueous solution.

• Solubility: Highly soluble in water (>700 g/L).

• Stability: Stable under normal storage conditions but inactivated by soil binding.

Mode of Action:

Paraquat inhibits photosystem I (PSI) by diverting electrons during photosynthesis, producing reactive oxygen species (ROS). These ROS cause rapid membrane damage, chlorosis, and necrosis of plant tissues. Being a contact herbicide, it only affects green tissues and does not move systemically within the plant.

Uses and Applications:

1. Weed Control Spectrum:

   • Broad-spectrum control of annual grasses, broadleaf weeds, and some perennial weed regrowth.

2. Application Areas:

   • Pre-plant burndown: Used to clear fields before planting crops.

   • Inter-row weed control: Common in crops like orchards, plantations, and vineyards where directed sprays avoid crop contact.

   • Non-crop areas: Roadsides, industrial sites, and fallow fields.

3. Action Speed:

   • Paraquat shows visible effects within hours of application, with complete desiccation in 1–3 days.

Benefits of Paraquat Aqueous:

• Rapid Action: Provides quick burn-down of green vegetation.

• No Soil Residual Activity: Safe for subsequent planting since it binds to soil particles and is inactivated.

• Resistance Management Tool: Effective against glyphosate-resistant weed species when used in rotation.

• Wide Utility: Used in multiple agricultural and non-crop settings.

Limitations:

• Non-Selective: Kills all green plant tissues upon contact, requiring precise application to avoid crop damage.

• No Systemic Effect: Ineffective on underground structures of perennial weeds.

• High Toxicity: Extremely toxic to humans and animals if ingested or inhaled.

• Regulatory Restrictions: Its use is tightly regulated or banned in several countries due to safety concerns.

Recommended Application:

• Dosage: 0.3–1.0 kg active ingredient per hectare, depending on weed type and growth stage.

• Method: Foliar spray using ground or aerial equipment with uniform coverage.

• Precautions:

  • Use shielded sprayers to avoid drift onto crops.

  • Always wear protective gear (gloves, respirator, goggles).

  • Do not apply on windy days to prevent drift injury.

Storage and Handling:

• Storage: Keep in original, tightly sealed containers in a cool, dry place.

• Shelf Life: Stable for 2–3 years under recommended conditions.

• Safety: Highly toxic; requires strict handling precautions to prevent accidental poisoning.

FAQ on Paraquat Aqueous:

Q1: How fast does Paraquat work?
A1: Symptoms appear within hours, and complete weed desiccation usually occurs within 1–3 days.

Q2: Does Paraquat have soil activity?
A2: No, it binds tightly to soil and becomes inactive, allowing planting soon after application.

Q3: Is Paraquat safe for crops?
A3: It is non-selective and can damage crops if contacted; application must be shielded or directed.

Q4: Why is Paraquat restricted in some regions?
A4: Due to its high acute toxicity to humans and lack of an antidote, many regions impose strict regulations or bans.