Pretilachlor: A Pre-Emergent Herbicide for Rice Weed Management

Definition:
Pretilachlor is a selective pre-emergent herbicide widely used in rice cultivation to control annual grasses, sedges, and some broadleaf weeds. It belongs to the chloroacetanilide class of herbicides and is commonly applied in flooded paddy fields either before or shortly after transplanting rice seedlings.

Chemical Characteristics of Pretilachlor:

• Chemical Name: 2-chloro-2′,6′-diethyl-N-(2-propoxyethyl)acetanilide

• Molecular Formula: C17H26ClNO2

• Molecular Weight: 311.85 g/mol

• Appearance: Pale yellow to light brown liquid (technical grade).

• Solubility: Sparingly soluble in water; readily soluble in organic solvents.

• Stability: Stable under normal storage; degrades in alkaline or highly aerobic soils.

Mode of Action:

Pretilachlor inhibits cell division and protein synthesis in germinating weed seeds, preventing shoot and root growth. It is absorbed mainly by coleoptiles (emerging shoots) of weeds before or shortly after emergence.

Uses and Applications:

1. Target Weeds:

   • Annual grasses: Echinochloa crus-galli (barnyard grass), Leptochloa chinensis.

   • Sedges: Cyperus difformis, Fimbristylis miliacea.

   • Some broadleaf weeds: Monochoria vaginalis, Ammania spp.

2. Crops:

   • Used mainly in transplanted and direct-seeded rice under flooded or moist soil conditions.

3. Application Timing:

   • Apply pre-emergence within 0–5 days after transplanting or sowing rice, before weed germination.

Benefits of Pretilachlor:

• Broad-Spectrum Grass Control: Effective against most grasses and sedges in rice fields.

• Safe for Rice: Low phytotoxicity under recommended conditions.

• Long Residual Action: Provides 3–4 weeks of weed suppression.

• Convenient Application: Can be applied pre-transplant or early post-transplant under flooded conditions.

Limitations:

• Limited Broadleaf Control: Requires mixing with broadleaf herbicides for complete control.

• Water Dependence: Needs a thin water layer in paddy fields for best results.

• Resistance Potential: Repeated use may encourage resistant weed biotypes.

• Crop Specificity: Restricted to rice cultivation and not suitable for dryland crops.

Recommended Application:

• Dosage: 0.75–1.25 kg active ingredient per hectare, depending on weed pressure.

• Method:

  • Apply uniformly in flooded fields as a pre-emergence soil surface treatment.

  • Maintain water level for at least 3–5 days after application to ensure efficacy.

• Precautions:

  • Do not apply on dry soil without adequate moisture.

  • Rotate with herbicides of different modes of action to reduce resistance risk.

Storage and Handling:

• Storage: Keep in tightly sealed containers in cool, dry, and well-ventilated areas.

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

• Safety: Low mammalian toxicity; wear gloves, masks, and protective clothing during handling.

FAQ on Pretilachlor:

Q1: What weeds does Pretilachlor control?
A1: It controls annual grasses, sedges, and a few broadleaf weeds in paddy rice fields.

Q2: When should Pretilachlor be applied?
A2: It should be applied within 0–5 days after transplanting or sowing rice, before weed emergence.

Q3: Can Pretilachlor be mixed with other herbicides?
A3: Yes, it is often mixed with broadleaf herbicides or other grass herbicides for a wider weed spectrum.

Q4: Is it safe for crops other than rice?
A4: No, it is crop-specific and primarily recommended for flooded rice systems.