Bentazone: A Selective Post-Emerent Contact Herbicide

Definition:
Bentazone is a selective, post-emergent contact herbicide belonging to the benzothiadiazole chemical family. It is primarily used to control broadleaf weeds and sedges in crops such as rice, beans, peanuts, maize, potatoes, and turf.

Chemical Characteristics of Bentazone:

• Chemical Name: 3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide

• Molecular Formula: C₁₀H₁₂N₂O₃S

• Molecular Weight: 240.28 g/mol

• Appearance: White to light tan crystalline solid (technical grade).

• Solubility: Highly soluble in water (~570 mg/L at 25°C).

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

Mode of Action:

Bentazone inhibits photosystem II (PSII) by binding to the D1 protein in the thylakoid membrane of susceptible plants. This blockage interrupts electron transport during photosynthesis, leading to chlorosis, necrosis, and eventual plant death. It acts primarily through foliar contact, requiring thorough leaf coverage for effectiveness.

Uses and Applications:

1. Target Weeds:

   • Broadleaf weeds: Amaranthus spp. (pigweed), Chenopodium spp. (lambsquarters), Xanthium spp. (cocklebur).

   • Sedges: Cyperus spp. (yellow nutsedge, rice flatsedge).

2. Crops:

   • Rice, maize, beans, peanuts, potatoes, soybeans, turfgrass, and some vegetables.

3. Timing:

   • Post-emergence: Applied to actively growing weeds during early stages for best results.

Benefits of Bentazone:

• Selective Control: Safe for labeled crops while targeting broadleaf weeds and sedges.

• Fast-Acting: Visible symptoms (chlorosis/necrosis) within a few days.

• Foliar Contact Action: Effective for emerged weeds without soil residual effects.

• Flexibility: Suitable for tank mixing with other herbicides for broader weed spectrum.

Limitations:

• No Soil Residual Activity: Does not prevent later weed emergence.

• Contact Herbicide: Requires good spray coverage for efficacy.

• Crop Sensitivity: Certain crops may show phytotoxicity at higher rates.

• Resistance Risk: Overuse may lead to resistant weed biotypes.

Recommended Application:

• Dosage: 0.5–1.5 kg active ingredient per hectare, depending on crop and weed size.

• Method: Foliar spray targeting small, actively growing weeds.

• Precautions:

  • Avoid spraying under drought stress or when weeds are hardened.

  • Use appropriate adjuvants for improved leaf penetration.

  • Prevent spray drift to sensitive crops.

Storage and Handling:

• Storage: Keep in original containers, away from moisture and sunlight.

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

• Safety: Low acute toxicity but use PPE; avoid contamination of water sources due to aquatic toxicity.

FAQ on Bentazone:

Q1: What is Bentazone used for?
A1: It is used post-emergence to control broadleaf weeds and sedges in crops like rice, beans, peanuts, and maize.

Q2: Does Bentazone control grasses?
A2: No, it is ineffective on grass weeds and targets only broadleaf weeds and sedges.

Q3: Is Bentazone systemic or contact-based?
A3: It is primarily a contact herbicide with limited systemic movement.

Q4: Can Bentazone be mixed with other herbicides?
A4: Yes, it is often tank-mixed with grass herbicides for complete weed control in crops.