Clethodim: A Selective Post-Emergent Grass Herbicide

Definition:
Clethodim is a systemic, selective post-emergent herbicide belonging to the cyclohexanedione (DIM) class. It is used for the control of annual and perennial grass weeds in broadleaf crops without affecting the crop itself.

Chemical Characteristics of Clethodim:

• Chemical Name: (E,E)-2-[1-[[(3-chloro-2-propenyl)oxy]imino]propyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one

• Molecular Formula: C₁₇H₂₆ClNO₃S

• Molecular Weight: 359.9 g/mol

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

• Solubility: Low water solubility but miscible in organic solvents.

• Stability: Stable under normal storage but sensitive to strong acids and bases.

Mode of Action:

Clethodim inhibits acetyl-CoA carboxylase (ACCase), an enzyme essential for fatty acid synthesis in grasses. This disrupts lipid production, leading to the death of meristematic tissues in grass weeds. Broadleaf crops remain unaffected because their ACCase enzyme is not sensitive to this herbicide.

Uses and Applications:

1. Target Weeds:

   • Annual grasses: Crabgrass (Digitaria spp.), foxtail (Setaria spp.), barnyardgrass (Echinochloa spp.).

   • Perennial grasses: Johnsongrass (Sorghum halepense), quackgrass (Elymus repens), Bermuda grass (Cynodon dactylon).

2. Crops:

   • Broadleaf crops such as soybeans, canola, cotton, sunflower, peanuts, vegetables, and ornamentals.

3. Application Timing:

   • Post-emergence: Applied when grasses are actively growing and at the recommended leaf stage.

Benefits of Clethodim:

• High Selectivity: Controls grasses without harming broadleaf crops.

• Systemic Action: Moves through the plant to the growing points for effective kill.

• Broad Grass Spectrum: Effective against both annual and perennial grasses.

• Flexible Mixing: Can be tank-mixed with broadleaf herbicides for wider weed control.

Limitations:

• No Control of Broadleaf Weeds: It targets only grass weeds.

• Slow Symptom Development: Takes 7–14 days for visible effects.

• Resistance Risk: Continuous use can lead to ACCase-resistant grass populations.

• Weather Sensitivity: Poor efficacy under cold or drought stress.

Recommended Application:

• Dosage: 0.2–0.4 kg active ingredient per hectare, depending on weed species and size.

• Method: Foliar spray with adequate coverage; add adjuvants (crop oil concentrate) to improve absorption.

• Precautions:

  • Apply on young, actively growing weeds for best results.

  • Avoid drift onto grass crops (e.g., maize, wheat).

  • Rotate herbicides to prevent resistance.

Storage and Handling:

• Storage: Keep in sealed containers, away from heat and sunlight.

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

• Safety: Low mammalian toxicity; avoid inhalation and direct contact. Toxic to aquatic organisms.

FAQ on Clethodim:

Q1: What weeds does Clethodim control?
A1: It selectively controls annual and perennial grass weeds but not broadleaf weeds.

Q2: Is Clethodim systemic or contact?
A2: It is a systemic herbicide, absorbed through foliage and translocated to weed meristems.

Q3: How long does it take to work?
A3: Initial symptoms (chlorosis) appear in 7–10 days, with full control in about 2–3 weeks.

Q4: Can it be mixed with other herbicides?
A4: Yes, it is often tank-mixed with broadleaf herbicides for complete weed management.