Chlorothalonil is a broad-spectrum contact fungicide that has been the backbone of disease management in turf, vegetables, and ornamentals since the 1960s. Its multi-site mode of action makes resistance development extremely rare. Recently banned in the EU but remains legal in the US.
🧪
Classification
Chloronitrile (Multi-site Contact Fungicide)
Signal Word
Warning (Danger for some formulations)
Mode of Action
Multi-site activity: disrupts multiple metabolic pathways in fungal cells simultaneously
Nearly all common fungal diseases: brown patch, dollar spot, leaf spot, anthracnose, powdery mildew, downy mildew, botrytis (gray mold), early blight, late blight, Septoria leaf spot, rust, scab. One of the broadest-spectrum fungicides available. The 'swiss army knife' of fungicides.
🏷️ Products & Brand Names
Daconil (GardenTech — the iconic homeowner brand), Bravo (professional turf), Echo (professional), Chlorostar, Quali-Pro Chlorothalonil. Available as liquid concentrate and ready-to-use spray.
⚠️ Safety & Precautions
Moderate toxicity — EPA Category I or II depending on formulation (some formulations carry "Danger" signal word). Eye irritant, skin sensitizer. Wear protective eyewear and gloves. Classified as a "likely human carcinogen" by EPA at chronic exposure levels — follow label strictly.
⚠️ Important: Banned in the EU since 2020 due to groundwater contamination and carcinogenicity concerns. Still legal and widely used in the US. Follow all label directions carefully, especially regarding water buffer zones and application frequency.
⚠️ Aquatic toxicity: Highly toxic to fish and aquatic invertebrates. Do not apply near ponds, streams, or drainage ditches. Observe all buffer zone requirements on the label.
Example
0.5 oz
per gallon
⚗️ Mixing Calculator
Enter your sprayer size and target rate — get the exact amount to pour. Backpack, hand sprayer, hose-end, or skid unit.
The resistance advantage: Unlike triazole fungicides (propiconazole, myclobutanil), chlorothalonil attacks fungi at multiple sites simultaneously. This makes resistance development extremely unlikely. It's the ideal rotation partner for site-specific fungicides.
Contact vs systemic: Chlorothalonil is strictly a contact/protectant fungicide — it does NOT enter the plant. It must be on the leaf surface BEFORE the fungal spore arrives. This means it's preventive only, not curative. Reapply every 7-14 days and after rain.
Vegetable garden hero: For tomato blight (early and late), chlorothalonil (Daconil) is one of the most effective homeowner options. Begin spraying before disease appears and maintain coverage throughout the season.
🐛 Pests This Treats — Learn More
Click any pest to view its full identification guide, biology, and treatment options.
💡 Broad-spectrum fungicide. Highly toxic to fish and aquatic invertebrates. EPA under review for environmental concerns.
❓ Frequently Asked Questions
Q: Is chlorothalonil safe for pets?
Follow the product label. Keep pets out of treated areas until completely dried (2–4 hours for sprays). Once dry, treated surfaces pose minimal risk to dogs and cats.
Q: Can I use chlorothalonil indoors?
Check the specific product label — formulations vary. Baits and dusts often have indoor labeling; concentrates and granulars are typically outdoor.
Q: How long does chlorothalonil last after application?
Residual varies by formulation, surface type, weather, and UV exposure. Indoor applications last longer than outdoor. Check the product label for re-application intervals.
Q: What should I do if exposed?
Remove contaminated clothing, wash skin with soap and water. For eye contact, rinse 15–20 minutes. For ingestion or severe symptoms, call Poison Control (1-800-222-1222). Have the product label available.
📋 Safety Data Sheet (SDS)
📋
Chlorothalonil Fungicide — Safety Data Sheet
View the official SDS document for this product directly on the CDMS label database.
💡 Did you know? Chlorothalonil was first registered in 1966 and has been applied billions of times worldwide. Its multi-site mode of action has kept it effective for nearly 60 years — one of the longest runs of any fungicide without significant resistance.
🔮
Reviewed by Derek GiordanoContent reviewed by a licensed pest management professional. Last reviewed: April 2026.
