Chlorothalonil Storage — Broad-Spectrum Fungicide Tank Selection

Chlorothalonil Storage — Broad-Spectrum Fungicide Tank Selection for Vegetables, Peanuts, Potatoes, Turf, and Ornamentals

Chlorothalonil (2,4,5,6-tetrachloroisophthalonitrile, CAS 1897-45-6) is a broad-spectrum multi-site contact fungicide registered in the United States since 1966 and remains, at the 2026 horizon, one of the highest-volume foliar fungicides applied in North American agriculture. Chlorothalonil acts by binding to and inactivating fungal-cell sulfhydryl groups across multiple metabolic pathways, which gives the chemistry a low fungicide-resistance profile and broad-spectrum activity against early blight, late blight, anthracnose, leaf spots, downy mildews, powdery mildews, and rusts. The chemistry is supplied as flowable concentrate (FlC, 720 g-ai/L = 6 lb-ai/gal aqueous suspension; e.g. Bravo Weather Stik, Daconil, Echo 720), wettable powder (WP, 75-90% ai dry), and water-dispersible granule (WDG, 75-90% ai dry granule). The flowable concentrate dominates retail-ag distribution and drives bulk-tank storage specification.

The six sections below cite EPA Registration Review for chlorothalonil; the EPA Interim Reregistration Eligibility Decision (IRED, 1999) classifying chlorothalonil as a "likely human carcinogen"; 40 CFR 152 + 156 (registration and labeling); 40 CFR 165 (container disposal); 40 CFR 170 (WPS); 40 CFR 180 (residue tolerances); OSHA 29 CFR 1910.1200; and Cole-Parmer + Plastics International compatibility tables.

1. Material Compatibility Matrix

Chlorothalonil flowable concentrate is an aqueous suspension of milled chlorothalonil technical solid in water with a wetting/suspending surfactant package and rheology modifiers. The pH range of typical commercial flowables is 6.0-8.5; the suspension is mildly acidic to neutral with no aggressive corrosion behavior on standard polyethylene tank construction. Chlorothalonil is photochemically stable on the leaf surface but degrades slowly in alkaline aqueous solution above pH 9 — a relevant constraint when tank-mixing with high-alkalinity carrier water or with alkaline foliar fertilizers.

The standard retail-ag bulk-storage specification for chlorothalonil flowable is 1,500-15,000 gallon HDPE vertical tank with EPDM gasket, PP-bodied ball valves with EPDM seats, and 304L stainless mixer for in-tank suspension agitation during the active vegetable-and-potato fungicide-spray season. Carbon-black-stabilized 1.9 SG resin is the durable outdoor specification.

2. Real-World Use Cases — Vegetables, Peanuts, Potatoes, Turf, Ornamentals

Vegetable Foliar Fungicide (Dominant Use). Chlorothalonil's largest use volume in North America is on vegetable crops: tomatoes, potatoes, cucurbits (cucumbers, melons, squash), brassicas (cabbage, broccoli, cauliflower), onions, celery, sweet corn, snap beans, carrots, and others. Application timing follows a 7-14 day spray interval starting at first-true-leaf or first-disease-symptom, with rates running 1.0-3.0 lb-ai/acre depending on the specific crop label and disease pressure. Tank-mix partners include copper hydroxide (Kocide), mancozeb, propiconazole, azoxystrobin, and other strobilurin and triazole fungicides for resistance-management rotation. Chlorothalonil's multi-site mode of action makes it a "rotation partner of last resort" in fungicide-resistance-management strategy; it has effectively zero documented field resistance after 60 years of commercial use.

Peanut Disease Management. Peanut leaf-spot (early leaf spot, late leaf spot, web blotch) management programs use chlorothalonil at 0.7-1.5 lb-ai/acre on a 14-day spray interval through the peanut growing season. Georgia, Alabama, Florida, North Carolina, and Texas peanut producers drive the second-largest US chlorothalonil use volume after vegetables.

Potato Late Blight Protection. Potato late-blight (Phytophthora infestans) protective-spray programs use chlorothalonil at 1.5-2.5 lb-ai/acre on 5-7 day spray intervals during high-disease-pressure periods. Wisconsin, Idaho, North Dakota, Maine, and Washington potato producers use chlorothalonil in tank mixes with mefenoxam, mandipropamid, dimethomorph, and copper-based fungicides.

Turf Disease Management. Golf-course and sod-farm turf disease management uses chlorothalonil (Daconil brand) for control of dollar spot, brown patch, anthracnose, and gray leaf spot at 3-8 oz/1,000 sq ft on 7-14 day spray intervals. Daconil is one of the most widely used golf-course fungicides in continued use.

Ornamental Plant Production. Greenhouse and nursery ornamental-plant production uses chlorothalonil for foliar disease control on flowering crops and nursery stock. Specialty applications include Christmas-tree disease management programs.

Aerial vs Ground Application. Chlorothalonil flowable is applied via ground self-propelled and pull-type sprayers at 10-30 gal/acre carrier rates and via fixed-wing and helicopter aerial application at 5-10 gal/acre carrier rates. Aerial application is permitted on the federal label with downwind-buffer requirements specific to chlorothalonil per the EPA Interim Decision mitigation measures.

3. Regulatory Framework — FIFRA, Carcinogen Classification, WPS, DOT

FIFRA Registration. Chlorothalonil products are registered under FIFRA (7 USC 136) with implementing regulations at 40 CFR 152 + 156 + 158. EPA Registration Review of chlorothalonil is ongoing through the 2026 horizon with multiple Endangered Species Act consultation and risk-assessment review processes. Verify the EPA Reg No. on the supplier label for procurement records. Chlorothalonil is generally NOT a Restricted Use Pesticide on the federal label; certain state classifications restrict use to certified applicators only (e.g. some Florida vegetable-production area restrictions).

EPA Interim Reregistration Eligibility Decision (IRED). The EPA 1999 IRED for chlorothalonil classified the chemistry as a "likely human carcinogen" (Group B2 under the EPA's now-superseded carcinogen classification scheme). Subsequent Registration Review iterations have maintained the carcinogen-of-concern designation while continuing US registration with enhanced PPE and re-entry mitigation. The 2018 EU pesticide-active-substance review concluded chlorothalonil approval should not be renewed; chlorothalonil registration ended in the European Union in 2020. US registration continues with mitigation measures.

Worker Protection Standard. Chlorothalonil agricultural use triggers WPS at 40 CFR 170 with REI of 12-48 hours per the specific product label and crop. Handler PPE per the label typically includes long-sleeved shirt + long pants + chemical-resistant gloves Category A per 40 CFR 170.607 + chemical-resistant footwear + protective eyewear + chemical-resistant apron during mixing-and-loading + dust/mist filtering respirator (NIOSH-approved N95 or P95) for some mixer/loader exposure scenarios.

Pesticide Container Disposal. Empty chlorothalonil containers (drums, mini-bulks, IBCs) are triple-rinsed or pressure-rinsed per 40 CFR 165. Refillable mini-bulk and IBC totes operate under refillable-container rules at 40 CFR 165.40-65.

Residue Tolerances. Chlorothalonil residue tolerances on food crops are established at 40 CFR 180.275, with crop-by-crop tolerance levels and pre-harvest interval (PHI) requirements on the product label. PHI ranges from 0 days (some leafy vegetable cuts) to 14-21 days (potatoes, peanuts, some fruit crops). Verify the specific PHI on the product label before each application.

DOT Shipping. Chlorothalonil flowable concentrate ships under UN 3082, Environmentally Hazardous Substance, Liquid, NOS, Class 9, Packing Group III. Mini-bulk and IBC totes ship in DOT 31HA1 or 31HA2 specification packaging.

OSHA Hazard Communication. Chlorothalonil SDS classifications include H317 (skin sensitization), H318 (eye damage), H330 (fatal if inhaled at high dust concentrations), H335 (respiratory irritation), H351 (suspected of causing cancer), H400 + H410 (very toxic to aquatic life with long-lasting effects).

4. Storage System Specification

Tank Sizing for Retail-Ag Dealer Bulk. Chlorothalonil retail-ag dealer bulk-storage installations typically use 1,500-15,000 gallon HDPE vertical tanks fed from rail-car or transport-truck delivery for the highest-volume vegetable and peanut producing regions (Florida, Georgia, North Carolina, Wisconsin, Michigan). Mini-bulk-tote (300-330 gallon IBC) cycling supports the lower-volume turf and ornamental segments.

Tank Sizing for Custom Applicator Field-Loading. Custom-application contractors serving vegetable, peanut, and potato producers use 1,500-3,000 gallon HDPE field-loading tanks. Dual-tank fill-and-dispense configurations support the high-throughput weekly fungicide-spray program rotations.

Secondary Containment. The federal floor at 40 CFR 264.175 sets containment at 10% of aggregate or 100% of the largest single tank. State pesticide-bulk-storage rules typically tighten to 110% of the largest tank. Vegetable and peanut producing-state bulk-storage regulations (e.g. Florida F.A.C. 5E-2.030, Georgia Rules of GDA Chapter 40-21) follow the standard pesticide-bulk-storage framework.

UV Stabilization. Outdoor chlorothalonil HDPE tanks specify carbon-black-pigmented resin for 15-20 year shell durability. Chlorothalonil itself is photochemically stable on the leaf but degrades slowly under UV in stored solution; opaque tank construction protects in-tank product stability.

Temperature Control. Chlorothalonil flowable tolerates 32-100°F without formulation degradation. Below freezing, the suspension can crystallize at the tank walls; warm-state vegetable producers (Florida, southern Georgia) have less freeze-protection concern than northern potato producers (Wisconsin, Michigan, North Dakota, Maine).

Agitation. Chlorothalonil flowable suspension settles over multi-month storage; daily 15-30 minute agitation cycles via in-tank mechanical mixer or recirculation pump are standard practice. For retail-ag dealer bulk tanks, programmable timer-control on a 304L stainless mixer with 1-2 HP gear-driven impeller is the durable specification.

pH Compatibility. Chlorothalonil degrades in alkaline aqueous solution above pH 9; tank-mix carrier-water alkalinity and high-pH foliar-fertilizer compatibility should be verified before tank-mixing. Acidifying buffers (Buffer Plus, LI-700) restore tank-mix pH to the 5-7 range for chlorothalonil stability.

5. Field Handling — Pumps, Valves, Gaskets, PPE, Spill Response

Pump Selection. Centrifugal pumps with cast-iron or 316L stainless casing and EPDM mechanical seal cover chlorothalonil flowable transfer service. Hypro, Banjo, and Ace are the standard ag-market brands. Diaphragm metering pumps with PVDF wetted parts are the precision-dosing specification for chemigation feed (Florida + California vegetable-producing regions).

Valve Specification. PP-bodied ball valves with EPDM seats cover the standard valve population. Bottom outlet valves on bulk tanks specify 2-inch or 3-inch full-port ball with PP body, EPDM seat, and stainless trim.

Gasket Material. EPDM is the standard chlorothalonil-flowable-service gasket. Viton (FKM) is the premium choice for multi-product sites.

PPE per WPS. Chlorothalonil handler PPE per the label includes: long-sleeved shirt + long pants + chemical-resistant gloves Category A per 40 CFR 170.607 + chemical-resistant footwear + protective eyewear + chemical-resistant apron during mixing-and-loading. Some products require a NIOSH-approved N95 or P95 dust/mist filtering respirator for certain mixer/loader exposure scenarios — verify on the specific product label. Skin sensitization (H317) is a real occupational concern; handlers with prior chlorothalonil exposure may develop contact-dermatitis allergic responses.

Spill Response. Chlorothalonil spills under 25 gallons are absorbed with vermiculite, clay, or commercial pesticide-absorbent pads, swept into a pesticide-waste drum, and disposed per state hazardous-pesticide-waste rules. Chlorothalonil CERCLA reportable quantity is not specifically listed in 40 CFR 302.4 (unlike many other pesticides); state pesticide-spill-reporting rules typically require notification within 24 hours of any spill above 5-gallon thresholds.

Container Triple-Rinse. Empty chlorothalonil containers are triple-rinsed at the sprayer fill operation per 40 CFR 165, with rinsate added to the sprayer tank for application. Triple-rinsed empty drums are recycled through the Ag Container Recycling Council network. Refillable mini-bulks and IBCs are returned to the distributor.

Aquatic-Toxicity Setbacks. Chlorothalonil federal-label setbacks from intermittent-stream and surface-water bodies (typically 30-60 feet for ground application, 100-300 feet for aerial application) apply at the application site. Salmonid-bearing-water-body setbacks may extend further per the EPA Interim Decision mitigation.

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