Machete (Butachlor): A Selective Pre-Emergence Herbicide for Rice Cultivation

Technical Introduction

Machete is the trade name of Butachlor, a chloroacetanilide herbicide developed for the pre-emergence control of annual grasses, sedges, and some broadleaf weeds in rice paddies. It is absorbed by emerging shoots and roots of weeds and disrupts protein, lipid, and nucleic acid synthesis, leading to poor germination and weed death.

• Mode of Action (MOA): Inhibits long-chain fatty acid synthesis in susceptible weeds.

• Selectivity: Rice crops rapidly metabolize Butachlor, giving them tolerance while controlling weeds.

• Formulation: Typically available as 50% EC (emulsifiable concentrate).

Applications

• Crops: Primarily rice (transplanted or direct-seeded). Sometimes used in wheat and vegetables in specific regions.

• Weeds Controlled:

  • Annual grasses:Echinochloa crus-galli (barnyardgrass), Digitaria spp. (crabgrass), Setaria spp. (foxtails)

  • Sedges:Cyperus difformis, Fimbristylis spp.

  • Broadleaf weeds:Ammania spp., Eclipta alba

• Timing: Applied as pre-emergence within 3–5 days of transplanting or seeding rice.

• Application Methods:

  • Broadcast spray on standing water (paddy field)

  • Pre-plant incorporation in some soil types

Advantages

• Highly Selective for Rice: Safe for transplanted paddy rice.

• Broad Spectrum: Controls major grassy weeds, sedges, and some broadleaves.

• Early Weed Management: Prevents weed competition in the critical early growth stage.

• Cost-Effective: Widely used in Asia due to low cost and proven reliability.

• Easy to Apply: Pre-emergence application reduces need for multiple post-emergence sprays.

Specifications (Typical Parameters)

FAQ

Q1: Is Machete safe for rice seedlings?
A: Yes, rice plants metabolize Butachlor efficiently, making it selective and safe when applied at recommended doses.

Q2: Can Machete control perennial weeds?
A: No, it is effective mainly against annual weeds; perennials may require additional management.

Q3: How long does Machete remain active in soil?
A: Typically 3–6 weeks, enough to protect rice during early establishment.

Q4: Can Machete be mixed with other herbicides?
A: Yes, it is often combined with bensulfuron-methyl, propanil, or 2,4-D to broaden the weed control spectrum.

Q5: Is resistance an issue with Butachlor?
A: Overuse in continuous rice systems has led to reduced sensitivity in Echinochloa spp. in some regions, so rotation and mixtures are recommended.