Oxadiazon: A Pre-Emergent Herbicide for Weed Control

Definition:
Oxadiazon is a pre-emergent herbicide widely used for controlling annual grasses, sedges, and broadleaf weeds in turfgrass, ornamentals, rice paddies, and non-crop areas. It belongs to the oxadiazole chemical class and is characterized by its soil-applied action, preventing weed germination and establishment.

Chemical Characteristics:

• Chemical Name: 2-tert-Butyl-4-(2,4-dichloro-5-isopropoxyphenyl)-Δ²-1,3,4-oxadiazolin-5-one

• Molecular Formula: C15H18Cl2N2O3

• Molecular Weight: 361.22 g/mol

• Appearance: White to light brown crystalline solid or granular formulation

• Solubility: Very low solubility in water; soluble in organic solvents

• Stability: Stable under normal conditions; adsorbs strongly to soil particles

Mode of Action:

Oxadiazon inhibits protoporphyrinogen oxidase (PPO), an enzyme involved in chlorophyll biosynthesis. This inhibition leads to the accumulation of reactive compounds that destroy plant cell membranes during germination, effectively killing weed seedlings before emergence.

Uses and Applications:

1. Target Weeds:

   • Annual grasses: Digitaria spp. (crabgrass), Echinochloa spp. (barnyardgrass)

   • Sedges: Cyperus spp.

   • Broadleaf weeds: Amaranthus spp., Portulaca spp.

2. Crops and Areas:

   • Turfgrass (golf courses, lawns, sports fields)

   • Rice paddies (flooded conditions)

   • Ornamental nurseries and landscaping

3. Application Timing:

   • Pre-emergence: Applied to soil before weed germination, often followed by irrigation to activate the herbicide.

Benefits:

• Long Residual Control: Provides extended weed suppression (6–8 weeks).

• Low Volatility: Minimal risk of drift or vaporization.

• Selective Safety: Safe for most established turf and ornamental plants when used correctly.

• Dual Use: Effective in both agricultural and non-agricultural settings.

Limitations:

• No Post-Emergent Activity: Does not control existing weeds.

• Surface Binding: Strongly adsorbed to soil; less effective on high-organic soils without proper incorporation.

• Crop Restriction: Not suitable for some newly seeded turf or sensitive plants.

• Water Management: Requires irrigation or rainfall to activate in dry soils.

Recommended Application:

• Dosage: Typically 1.5–4.0 kg active ingredient per hectare (rate varies by crop and soil).

• Method:

  • Apply uniformly to soil or turf surface.

  • Water-in lightly after application to activate.

• Precautions:

  • Do not disturb treated soil after application.

  • Avoid using on freshly seeded or sprigged turfgrass.

Storage and Handling:

• Storage: Store in sealed containers, in a dry, ventilated area away from food or feed.

• Shelf Life: Typically stable for 2–3 years under proper storage.

• Safety: Low mammalian toxicity but harmful to aquatic organisms; avoid contamination of water bodies.

FAQ on Oxadiazon:

Q1: Can Oxadiazon be used on newly planted turf?
A1: No, it should only be applied on established turfgrass to avoid phytotoxicity.

Q2: Does it control existing weeds?
A2: No, it is strictly a pre-emergent herbicide and ineffective against emerged weeds.

Q3: Is it safe for rice paddies?
A3: Yes, Oxadiazon is registered for pre-emergent weed control in flooded rice systems.

Q4: How long does its weed control last?
A4: Residual control typically lasts 6–8 weeks, depending on soil and environmental conditions.