Mancozeb

Mancozeb is a contact fungicide belonging to the dithiocarbamate group, widely used in the preventive control of fungal diseases in various agricultural crops.

It is characterized by its multisite action, presenting a low risk of developing resistance in pathogens. It is effective against powdery mildew, mildew, rust, leaf spots and anthracnose in crops such as potatoes, tomatoes, grapes, citrus, coffee, soybeans and vegetables.

Its application requires careful handling due to toxicological and environmental restrictions, being classified as a class II product (highly toxic).

Chemical identification

Common name (ISO): mancozeb

Official chemical name: coordination complex of manganese ion with zinc ion of ethylenebis(dithiocarbamate)

Gross chemical formula: C8H12MnN4S8Zn

CAS number: 8018-01-7

Chemical class: Dithiocarbamate

Molecular structure:

• Molecular weight: 541,1g/mol

• Organometallic complex containing manganese and zinc coordinated with dithiocarbamate ligands

Historic: Developed by Rohm and Haas Company in the 1960s, mancozeb was introduced to the agricultural market in 1961. It represents an evolution of sulfur and copper-based fungicides, offering greater efficacy and a broader spectrum of control. In Brazil, it was first registered in the 1970s, becoming one of the most widely used fungicides in national agriculture.

Mode of action

Specific biochemical mechanism: Mancozeb acts as a multisite fungicide, interfering in multiple metabolic pathways of pathogenic fungi. Its main action occurs through the inhibition of enzymes containing sulfhydryl groups (-SH), essential for the energy metabolism and protein synthesis of fungi.

Biochemical target: cysteine ​​sulfhydryl groups in critical enzymes such as pyruvate dehydrogenase, succinate dehydrogenase, aconitase, Krebs cycle enzymes.

FRAC Group: M (Multisite) - Code M3

Physiological consequences in the pathogen: Enzyme inhibition results in impaired cellular respiration, ATP synthesis, cell wall formation, and nuclear division. This leads to pathogen cell death by widespread metabolic collapse, preventing spore germination and hyphal growth.

Control Spectrum

Some examples of fungi controlled by mancozeb, divided by cultures...

Potato (Solanum tuberosum): burn (Phytophthora infestans), black spot (Alternaria Solani). Dose: 1,5-3,0 kg bw/ha

Tomato (Solanum lycopersicum): burn (Phytophthora infestans), black spot (Alternaria Solani), septoria (Septoria lycopersici). Dose: 2,0-3,0 kg bw/ha

Grape (Vitis vinifera): mildew (plasmopara viticola), anthracnose (Elsinoe ampelina). Dose: 2,0-4,0 kg bw/ha

Coffee (Coffea arabica): rust (Hemileia vastatrix), cercosporiosis (Cercospora coffeicola). Dose: 2,5-4,0 kg bw/ha

Soy (Glycinemax): Asian rust (Phakopsora pachyrhizi), target spot (Corynespora cassiicola). Dose: 1,5-2,5 kg bw/ha

Safety intervals:

• PHI (Pre-harvest): 7-21 days (varies depending on crop)

• REI (Re-entry): 24-48 hours after application

Resistance Management

Resistance history: Due to its multisite mode of action, mancozeb presents a low risk for the development of resistance. Documented cases of resistance are rare, limited to a few populations of plasmopara viticola in Europe after intensive use for decades. In Brazil, there are no confirmed reports of resistance to mancozeb under field conditions.

Management recommendations:

• Rotation with fungicides from different FRAC groups (triazoles - FRAC 3, strobilurins - FRAC 11, SDHI - FRAC 7)

• Use in mixture with site-specific fungicides to reduce selection pressure

• Preventive application respecting recommended intervals

• Constant monitoring of field effectiveness

Dosing strategies: It is recommended to use full doses (high rate) in conditions of high disease pressure, avoiding subdoses that may favor the selection of less sensitive isolates.

Safety and Environmental Impact

Toxicological classification: class II - highly toxic (yellow band)

Persistence in soil:

• Half-life (DT50): 7-30 days in tropical conditions

• Koc: 1.000-5.000 mL/g (moderate to strong adsorption)

• Degradation by hydrolysis and microbial action

Leaching potential: low to moderate risk of groundwater contamination due to adsorption to soil and relatively rapid degradation. The greatest concern is the formation of metabolites such as ETU, which are more mobile.

Risk to non-target organisms:

• Bees: moderately toxic (oral LD50 > 100 μg/bee)

• Fish: highly toxic (LC50 96h: 1-10 mg/L for many species)

• Aquatic organisms: require special care near bodies of water

• Birds: moderately toxic (LD50 > 2.000 mg/kg)

Interactions and Compatibilities

Possible mixtures: triazole fungicides (tebuconazole, propiconazole); strobilurins (azoxystrobin, pyraclostrobin); copper fungicides in low concentrations; non-ionic adjuvants

Prohibited or problematic mixtures: alkaline products (pH > 8,0) cause decomposition; mineral oils in high concentrations; foliar fertilizers with high iron concentrations

Phytotoxicity: rare when used at recommended doses, but may occur in:

• Applications under severe water stress conditions

• Mixing with oils at high temperatures (> 30°C)

• Overlapping applications with very short intervals

Agronomic Efficiency and Strategic Positioning

Conditions affecting effectiveness:

• Rain: washing after 2-4 hours significantly reduces effectiveness

• Temperature: reduced effectiveness above 35°C due to volatilization

• Humidity: greater effectiveness in high relative humidity conditions

• pH of the syrup: optimal between 6,0-7,0

Competitive advantages: broad spectrum of control; low risk of resistance; adequate residual action (7-14 days); compatibility with integrated programs; relatively low cost.

Limitations: absence of curative or eradicating action; toxicological and environmental restrictions; need for frequent reapplications; climatic limitations for application.

Strategic positioning by system:

• Soy - preventive use at the beginning of the reproductive period (R1-R3), alternating with triazoles and strobilurins for management of Asian rust.

• Corn - preventive application in V8-VT for control of helminthosporiosis and cercosporiosis, especially in high-tech systems.

• Cotton - positioning in the middle third of the crop to control ramularia and alternaria, in rotation with SDHI.

• Coffee - preventive use before the rainy season to control rust, interspersed with systemic triazoles.

• Sugar cane - application on seedlings and young plants to control rust and helminthosporiosis.

• Vegetables - basis of preventive programs, especially to control mildews and late blight on solanaceae and cucurbits.