Hexazinone: A Broad-Spectrum Systemic Herbicide

Definition:
Hexazinone is a systemic, broad-spectrum herbicide primarily used for pre-emergent and post-emergent control of annual and perennial weeds, shrubs, and woody plants. It belongs to the triazine class of herbicides and is commonly used in non-crop areas, industrial sites, forestry, and certain crop systems like alfalfa and sugarcane.

Chemical Characteristics of Hexazinone:

• Chemical Name: 3-Cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione

• Molecular Formula: C₁₂H₂₀N₄O₂

• Molecular Weight: 252.3 g/mol

• Appearance: White crystalline solid.

• Solubility: Highly soluble in water (approx. 33 g/L at 25°C).

• Stability: Stable under normal conditions; persists in soil but degrades via microbial activity.

Mode of Action:

Hexazinone inhibits photosystem II (PSII) in plants, disrupting electron transport during photosynthesis. This leads to energy depletion, chlorosis, necrosis, and ultimately plant death. It is absorbed by both roots and foliage, making it effective for soil and foliar applications.

Uses and Applications:

1. Target Weeds:

   • Annual and perennial grasses.

   • Broadleaf weeds such as pigweed and ragweed.

   • Woody species like oak and pine in forestry applications.

2. Crops and Non-Crop Areas:

   • Crops: Sugarcane, alfalfa, pineapple.

   • Non-Crop: Roadsides, railways, industrial sites, rights-of-way, and forestry plantations.

3. Application Timing:

   • Pre-emergence: Prevents weed germination in soil.

   • Post-emergence: Controls established weeds through foliar uptake.

Benefits of Hexazinone:

• Broad-Spectrum Control: Effective on grasses, broadleaf weeds, and woody plants.

• Flexible Use: Can be used in both soil and foliar applications.

• Long Residual Activity: Provides extended weed control in non-crop and forestry areas.

• Compatibility: Often used in combination with other herbicides for enhanced efficacy.

Limitations:

• Non-Selective: Can injure desirable plants if not applied precisely.

• Environmental Risk: High water solubility increases leaching potential and groundwater contamination risk.

• Persistence: Long residual activity may limit rotational cropping options.

Recommended Application:

• Dosage:

  • Non-crop/industrial: 1–6 kg active ingredient per hectare.

  • Alfalfa and sugarcane: 0.5–2 kg a.i./ha depending on weed pressure.

• Method: Ground or aerial spraying with uniform coverage.

• Precautions:

  • Avoid application near water bodies.

  • Use calibrated equipment to prevent over-application.

  • Rotate with herbicides of different mechanisms to delay resistance.

Storage and Handling:

• Storage: Keep in sealed containers, in a cool, dry, ventilated location.

• Shelf Life: Stable for 2–3 years if stored correctly.

• Safety: Use protective equipment; toxic to aquatic plants and organisms.

FAQ on Hexazinone:

Q1: What is Hexazinone used for?
A1: It is widely used for non-crop weed control, forestry site preparation, and selective use in crops like alfalfa and sugarcane.

Q2: How does Hexazinone work?
A2: It inhibits photosynthesis by blocking photosystem II in susceptible weeds.

Q3: Does Hexazinone have soil activity?
A3: Yes, it provides strong soil residual activity, controlling weed germination over time.

Q4: Can Hexazinone harm desirable plants?
A4: Yes, it is non-selective in many cases and must be carefully applied to avoid drift or leaching near sensitive plants.