Diclofop-methyl (D): A Post-Emergent Grass Herbicide

Definition:
Diclofop-methyl is a selective, post-emergent herbicide belonging to the aryloxyphenoxypropionate (AOPP) group. It is primarily used to control annual grass weeds in cereal crops such as wheat and barley while being safe for broadleaf crops.

Chemical Characteristics of Diclofop-methyl:

• Chemical Name: Methyl (RS)-2-[4-(2,4-dichlorophenoxy)phenoxy]propionate

• Molecular Formula: C₁₆H₁₄Cl₂O₄

• Molecular Weight: 341.2 g/mol

• Appearance: Pale yellow to brown liquid or emulsifiable concentrate.

• Solubility: Insoluble in water; soluble in organic solvents.

• Stability: Stable under normal conditions; hydrolyzes slowly in alkaline environments.

Mode of Action:

Diclofop-methyl is absorbed by grass leaves and metabolized to diclofop acid, which inhibits acetyl-CoA carboxylase (ACCase). This enzyme is essential for fatty acid synthesis in grasses, leading to growth inhibition, chlorosis, and plant death.

Uses and Applications:

1. Target Weeds:

   • Annual grasses: wild oat (Avena fatua), annual ryegrass (Lolium rigidum), foxtail (Setaria spp.), and other small grass weeds.

   • Ineffective on broadleaf weeds and perennial grasses.

2. Crops:

   • Used in wheat, barley, and rye.

   • Sometimes applied in non-crop areas to target annual grass infestations.

3. Timing:

   • Post-emergence, when grasses are at the 2–4 leaf stage and actively growing.

Benefits of Diclofop-methyl:

• Selective Control: Targets grass weeds without harming broadleaf crops.

• Fast Uptake: Absorbed quickly through leaves and translocated to growing points.

• Complementary in Tank Mixes: Often mixed with broadleaf herbicides for broader weed control in cereals.

Limitations:

• No Soil Activity: Lacks residual control; does not prevent future weed germination.

• Weed Resistance: Repeated use has led to ACCase-resistant grass populations.

• Crop Restrictions: Cannot be used in crops like maize, rice, or sorghum due to crop injury risk.

Recommended Application:

• Dosage: 0.5–1.0 kg active ingredient per hectare, depending on weed species and density.

• Method: Foliar spray ensuring thorough weed coverage.

• Precautions:

  • Apply to small, actively growing weeds for best results.

  • Avoid drift to sensitive crops and water bodies.

  • Rotate herbicides to delay resistance development.

Storage and Handling:

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

• Shelf Life: 2–3 years under proper conditions.

• Safety: Use protective gear; toxic to aquatic organisms.

FAQ on Diclofop-methyl:

Q1: What weeds does Diclofop-methyl control?
A1: It is effective against annual grasses such as wild oats, annual ryegrass, and foxtail but not broadleaf weeds.

Q2: Does it provide residual control?
A2: No, it is a contact herbicide without soil persistence.

Q3: Can Diclofop-methyl be mixed with other herbicides?
A3: Yes, it is often combined with broadleaf herbicides in cereal crop programs.

Q4: How to manage resistance?
A4: Rotate with herbicides from different modes of action and use integrated weed management practices.