Chlorothalonil

Introduction

Chlorothalonil (FRAC M05) acts on multiple fungal targets, providing robust protectant activity and excellent resistance-management value. It was long favored against septoria in wheat, late blight in potatoes, and turf diseases like dollar spot.

Regulatory Status

• EU: Approval withdrawn (2019) due to concerns about carcinogenic metabolites and groundwater exposure; use ceased.
• US & other regions: Still registered with restrictions; label evolves as risk assessments update.

Use Patterns & Agronomy

• Crops: Cereals, potatoes, peanuts, vegetables; turfgrass on golf/sports surfaces.
• Role: Front-loaded in programs to protect leaf tissue; often alternated with single-site SDHI/QoI/triazole mixes to extend their life.
• Strengths: Broad spectrum, low resistance risk; weatherfast when applied properly.
• Limitations: Purely contact (no curative action); requires diligent interval management.

Environmental & Safety

• Concerns center on aquatic toxicity and metabolite profiles; mandates include buffer zones, drift mitigation, and water protection measures in registered geographies.

Outlook

In Europe, growers have re-optimized programs without chlorothalonil, often at higher cost and greater resistance pressure on single-site fungicides. Where still registered, it remains a key protectant but under increasing scrutiny; expect tighter stewardship and continued searches for multi-site replacements (e.g., folpet in some programs).

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