Imazethapyr: Selective Herbicide for Post-Emergence Weed Control

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2025-08-25 09:21

Technical Introduction

Imazethapyr is an imidazolinone herbicide used for pre- and post-emergence control of grasses, broadleaf, and sedge weeds in legume crops. It is absorbed by roots and foliage and moves systemically throughout the plant.

Mode of Action (MOA): Inhibits acetolactate synthase (ALS), an enzyme critical for the synthesis of branched-chain amino acids (valine, leucine, isoleucine). This disruption halts protein synthesis and cell division, ultimately leading to plant death.
Systemicity: Highly systemic; translocated via both xylem and phloem.
Formulations: Typically available as 95% TC, 10% SL, 2% GR, and other soluble liquid forms.

Applications

Crops:
- Soybean
- Peanut
- Alfalfa
- Beans (dry beans, green beans, mung beans)
- Other legume crops
Weeds Controlled:
- Grasses: Echinochloa crus-galli (barnyardgrass), Digitaria spp., Setaria spp.
- Broadleaf: Amaranthus spp., Chenopodium album, Polygonum spp., Eclipta alba
- Sedges: Cyperus rotundus, Cyperus iria
Application Timing:
- Pre-emergence: Applied to soil immediately after sowing.
- Post-emergence: Applied when weeds are in the 2–4 leaf stage for maximum efficiency.

Advantages

Broad-Spectrum Control: Effective against grasses, broadleaf weeds, and sedges.
Long Residual Action: Provides up to 4–6 weeks of control with a single application.
Crop Selectivity: Designed for use in legumes; crops metabolize the herbicide quickly.
Systemic Movement: Controls weeds even after absorption through roots or leaves.
Low Use Rate: Effective at relatively low application doses, reducing chemical load.

Specifications (Typical Parameters)

Parameter	Description	Typical Value
Common Name	Imazethapyr
Chemical Class	Imidazolinone herbicide (ALS inhibitor)
Chemical Formula	C₁₅H₁₉N₃O₃
Molecular Weight	~289.33 g/mol
Appearance	White to light brown crystalline solid
Purity (TC)	≥ 95%
Common Formulations	95% TC, 10% SL, 2% GR
Application Rate	50–100 g a.i./ha (varies by crop & weed pressure)
Mode of Action	ALS inhibition → protein synthesis halted → plant death
Persistence	4–6 weeks residual activity
Toxicity	Oral LD₅₀ (rat) > 5,000 mg/kg (very low toxicity)

FAQ

Q1: Is Imazethapyr safe for non-legume crops?
A: No, it is selective only for legume crops like soybean, peanut, and beans. It may cause severe injury to cereals or vegetables if misapplied.

Q2: Can it control sedges like purple nutsedge (Cyperus rotundus)?
A: Yes, Imazethapyr has good efficacy against sedges, making it more versatile than some other ALS inhibitors.

Q3: Is Imazethapyr residual in soil?
A: Yes, it has a residual activity of 4–6 weeks, which suppresses later-emerging weeds. However, long persistence in some soils may affect sensitive rotational crops.

Q4: What is the best stage for post-emergence application?
A: When weeds are in the 2–4 leaf stage and actively growing for optimum absorption.

Q5: Is resistance a concern?
A: Yes, ALS inhibitor resistance has been documented in Amaranthus, Echinochloa, and Chenopodium species. Crop rotation and herbicide rotation are essential.