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.
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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)
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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.
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Reviewed by Derek GiordanoContent reviewed by a licensed pest management professional. Last reviewed: April 2026.
No active ingredient is universal, and Chlorothalonil Fungicide has specific weak points worth understanding before purchase. Resistance is the most common limitation — populations in heavily-treated areas (commercial kitchens, multi-unit housing, urban cores) often show measurable tolerance compared to populations in less-treated environments. Rotating between chemical classes every two or three applications reduces resistance pressure significantly.
Substrate binding is another limitation. Chlorothalonil Fungicide on highly absorbent surfaces like unfinished wood or carpet can become bound to the substrate within hours of application and never reach the pest in active form. For these surfaces, dust formulations or baits perform better than liquid sprays. Crack-and-crevice application using a precision tip places product where it reaches the pest while minimizing exposed-surface residue.
Pollinator and beneficial-insect impact is the third limitation to plan around. Outdoor application timing should avoid blooming plants, and any application near beneficial habitat (gardens, water features, pollinator strips) should be made in late evening when beneficials are inactive.
How Chlorothalonil Fungicide performs in real-world conditions
Laboratory efficacy numbers for Chlorothalonil Fungicide rarely match field performance, and the gap is wider for some product categories than others. Residual life on porous surfaces (brick, unsealed wood, concrete) is typically 30 to 50 percent shorter than on the sealed lab surfaces used in registration data. Direct sunlight reduces persistence further — UV breakdown can cut a 90-day residual to under 45 days on south-facing exterior walls. For interior treatments these effects are smaller, but humidity, cleaning products, and foot traffic all reduce real-world residual life.
Temperature interaction is equally important. Chlorothalonil Fungicide, like most modern active ingredients, has an optimal temperature window for both delivery and pest susceptibility. Outside that window, the same dose may underperform by half. Field operators usually adjust application timing rather than rate to compensate, since increasing the rate beyond label specification produces diminishing returns and increases off-target risk.
Mixing partners and tank-mix compatibility also affect real-world performance. Adding an insect growth regulator extends control by addressing eggs and immatures that the adulticide misses. The cost premium for a tank mix is usually under 20 percent and doubles the effective control window.
Practical safety considerations for Chlorothalonil Fungicide
The label is the law, and it covers the legal minimum. Practical safety for Chlorothalonil Fungicide in a household setting goes beyond label compliance — children, pets, and food-contact surfaces all merit precautions above the regulatory floor. Re-entry intervals on consumer labels are typically calibrated for healthy adults; for nurseries, pet bedding areas, and pregnant-occupant homes, doubling the indicated interval is a reasonable default.
Ventilation matters more than most homeowners realize. Even low-VOC formulations release detectable airborne residues for several hours post-application, and an HVAC system that is running during treatment will redistribute those residues throughout the structure. Standard practice is to turn off forced air for the treatment window and the first hour after, then run on high circulation for 30 minutes before normal occupancy resumes.
Personal protective equipment listed on the label is the minimum. For larger volumes, a half-face respirator with organic-vapor cartridges adds meaningful protection at modest cost. Nitrile gloves outperform latex for solvent-based formulations and are inexpensive enough to use single-use.
Published: Jan 1, 2025 · Updated: Apr 7, 2026
Storage and disposal of pesticide products
Pesticide storage and disposal practices have meaningful safety and environmental implications that many homeowners overlook. Storage practices that matter: keep products in original containers with intact labels (decanting is a documented poisoning cause and makes label-required information unavailable when needed), store in a locked area or cabinet inaccessible to children and pets, separate from food and animal feed, in a temperature-controlled location (extreme cold and extreme heat both degrade many products), and elevated above floor level to prevent contamination from spills. Disposal practices: never pour unused products down drains, on the ground, or into household trash; consult the label disposal instructions and your municipality's household hazardous waste program (most jurisdictions have collection events or permanent sites), and use up small remaining quantities at label rates rather than disposing of partial containers when possible. Empty containers, after triple rinsing as the label specifies, can typically go in recycling or trash per the label, but rinsate must be applied as the original product would be.
Pest pressure as a property value signal — and how to address it before listing
Pest issues directly affect property valuation in several documented ways: termite damage is a standard inspection finding that can derail closings or require significant credits; rodent activity in attics and crawlspaces flags during inspections and creates buyer concerns about hidden damage; visible cockroach or bedbug activity raises the question of what else has been neglected. Sellers who address pest issues before listing — ideally with documentation of treatment and a clean follow-up inspection — preserve more value than those who try to negotiate around buyer-discovered issues. The investment is typically modest relative to the price impact: a pre-listing inspection by a licensed pest control company runs a few hundred dollars in most markets, and resolving common findings (rodent exclusion, ant treatment, wasp nest removal) is rarely a significant expense. The value preservation comes from removing inspection findings as negotiation leverage, not from any single repair.
Pesticide rotation and the resistance management problem
Resistance management — using multiple active ingredients in sequence so that no single mode of action selects for resistant individuals — is standard practice in agricultural and commercial pest control but rarely makes it into residential treatment decisions. The underlying concern is real: chronic use of a single pyrethroid product against bed bugs has produced widespread pyrethroid resistance, with some populations now showing resistance factors of 1000x or more. The same pattern is documented in German cockroach resistance to chlorpyrifos and other historical actives, mosquito resistance to organophosphates in heavy-use regions, and house fly resistance across multiple compound classes. For residential treatment, the practical implication is to avoid using the same active ingredient repeatedly across multiple treatment cycles; rotating between products in different chemical families (e.g., pyrethroid → neonicotinoid → insect growth regulator → carbamate, or whatever subset is appropriate to the target pest) reduces selection pressure and preserves efficacy. The product label specifies the active ingredient family, allowing rotation choices to be made on actual chemistry rather than brand name.
Seasonal pest calendars: building one for your specific property
Generic seasonal pest calendars list typical activity windows by region, but every property has its own micro-calendar shaped by orientation, vegetation, drainage, neighbor properties, and structural features. After one or two years of observation, most homeowners can map their property's specific patterns: when wasps start scouting (typically early to mid spring as queens emerge), when ants first appear indoors (often after a specific rain pattern), when stored-product pests show up in pantries (often late spring through fall), when rodent activity increases (typically late fall as outdoor food declines and indoor warmth attracts them), when mosquito pressure peaks (varies enormously by local conditions), and when seasonal nuisances like cluster flies or boxelder bugs arrive (usually first hard cooling in fall). A personal calendar drives preventive timing — exterior perimeter treatment shortly before ant pressure builds is dramatically more effective than treatment after they're inside, exclusion work for rodents in early fall beats trapping in late fall, and wasp prevention in early spring beats removal in summer. Two years of observation produces a calendar more useful than any published guide for the specific property.
Application timing within the day and weather conditions
Pesticide applications produce significantly different results depending on application timing, and matching application to conditions improves outcomes substantially. For outdoor liquid applications, early morning (after dew has evaporated, before pollinators are active) and late evening (after pollinators have stopped foraging, before evening dew) produce best results: temperatures are moderate, wind is typically lower, and non-target exposure is reduced. Mid-day applications during high temperatures cause volatility losses and faster degradation. For interior treatments, timing depends on the pest: cockroach baiting works at any time but should follow rather than precede cleaning; bed bug treatments need to follow vacuuming and clutter reduction; ant baits work best when active trails are present, which often means specific times of day for specific species. Rain within 4 hours of outdoor liquid application washes off most surface residue except specifically rainfast formulations; checking the next 24-hour forecast before any outdoor treatment is the basic discipline that prevents this loss. Temperatures above 90°F or below 50°F outside the product label's recommended range produce reduced efficacy.
Reduced-risk pesticide selection: a category worth knowing
The EPA's reduced-risk pesticide program identifies active ingredients and formulations that meet specific criteria for lower toxicity to non-target organisms, reduced potential for groundwater contamination, lower likelihood of resistance development, or better compatibility with integrated pest management. Products in this category aren't free of toxicity — they're pesticides, and all pesticides have some toxic profile — but they represent the lower end of the risk distribution within their pest categories. For homeowners who want to use pesticides but are concerned about minimizing exposure and environmental impact, looking for products with reduced-risk actives is a defensible filter. Examples include some of the diamide insecticides, spinosyns, and certain microbial products. The catch is that retail availability lags behind the professional market for many reduced-risk products, and consumer pesticide aisles still skew heavily toward older pyrethroid and carbamate formulations. For homeowners willing to source products from agricultural supply channels or work with a pest control company that uses these products, the option exists; for those buying off the shelf at typical retail, the choices are narrower.
Pest control warranties: reading the fine print before signing
Pest control warranties are not standardized, and the differences between contracts that look superficially similar can be enormous. Termite warranties in particular vary across at least three significant dimensions: whether they cover retreatment only or also include damage repair, whether the damage coverage is capped or unlimited, and whether the warranty is transferable to subsequent owners. A retreatment-only warranty on a property with significant termite pressure is much weaker than a damage-inclusive warranty, and the difference matters most precisely in the situations where the warranty is most likely to be needed. General pest control service agreements often have similar gradations — some include unlimited callbacks during the service period, some include a fixed number, and some charge for any visit outside the regular schedule. Before signing, the question to ask is not whether the contract has a warranty, but exactly what the warranty covers, what triggers a callback at no charge, and what the renewal terms are. Companies rarely volunteer this clearly; reading the document carefully and asking specific questions is on the homeowner.
Pesticide drift and the neighbor dimension
Pesticide drift — the off-target movement of applied product through air, water, or runoff — is an under-discussed dimension of residential pesticide use, but it's an increasingly common source of conflict between neighbors and a real factor in the cumulative environmental load of pesticide use. Foliar sprays applied in even light wind drift further than most homeowners expect, particularly with finer droplet sizes. Granular products applied near property lines wash into adjacent properties in significant rainfall. Mosquito fogging can move across multiple properties depending on conditions. The implications are partly legal — drift onto neighboring property without consent has been the basis of successful nuisance claims in some jurisdictions — and partly ethical. Applying products only in low-wind conditions, choosing coarser droplet sizes when possible, using granulars rather than sprays near property lines, and timing applications to avoid imminent rainfall all reduce drift. For homeowners concerned about pesticide exposure from neighbors' applications, the productive conversation is usually about timing and product choice rather than about pesticide use in general, and approaching it that way tends to produce cooperation rather than escalation.
