The Continued Use Of Mancozeb, An Effective Fungicide

Mancozeb is a widely used fungicide belonging to the dithiocarbamate chemical group. It is effective in controlling a broad spectrum of fungal diseases on fruits, vegetables, and other crops. Commercially, it has been used in many countries because it has such a broad spectrum of activity. Has been considered to be of low toxicity and extremely cheap to use and apply. Its cost effectiveness is based on the fact that there are no other fungicides that can act with such great efficacy.

Chemically, it is a manganese ethylenebis (dithiocarbamate) polymeric complex with a zinc salt. It is classified as an ethylene bisdithiocarbamate (EBDC) fungicide (Pertha et al., 2017). The fungicide is registered under the tradename of Dithane 75 DF by the US Environmental Protection Agency (EPA).

EBDCs are unstable when exposed to oxygen as in air, moisture and of course in biological systems. A number of degradation products are formed including ethylenethiourea (imidazolidine-2-thione,ETU) (Lentza-Rizos 1990).

1. Mechanism of Action

Mancozeb functions by inhibiting the activity of fungal enzymes critical for cellular respiration. Specifically, it interferes with the metabolism of lipids and the formation of cellular membranes in fungi. It is very effective at inhibiting the germination of fungal spores.  It acts as a contact fungicide, meaning it prevents fungal growth on the plant surface without systemic absorption into plant tissues.

2. Permitted Usage in Countries

The regulatory status of Mancozeb varies across countries.

• Permitted:
  Mancozeb is still widely permitted in countries such as India, Brazil, China, Mexico, South Africa, and many developing nations. It remains a vital fungicide for protecting crops where alternative solutions may be less accessible or effective.
• Restricted/Banned:
  In regions like the European Union, Mancozeb was banned in 2021 due to concerns over its potential health and environmental impacts. The decision primarily stemmed from its classification as a suspected endocrine disruptor and possible human health risks. Similarly, in the United States, its use has been phased out in some areas due to updated safety regulations, although it may still be used under specific circumstances.

Farmers are advised to check local regulations as policies can evolve.

3. Application on Fruits and Vegetables

Mancozeb is known for its effectiveness against diseases caused by fungal pathogens such as Alternaria, Phytophthora, and Downy Mildew. It is particularly effective on:

• Fruits: Apples, bananas, grapes, mangoes, citrus fruits, and pears.
• Vegetables: Tomatoes, potatoes, onions, cucumbers, carrots, and lettuce.
• Other Crops: Wheat, rice, and nuts (e.g., almonds).

Its protective barrier prevents diseases like early and late blight in potatoes and tomatoes, anthracnose in mangoes, and black spot in citrus.

4. Toxicity Issues

While effective, Mancozeb has raised significant concerns regarding its potential impact on human health and the environment. 

• Human Health Concerns:
  • Acute Exposure: Mancozeb can irritate the skin, eyes, and respiratory system if proper protective equipment isn’t used during handling or application.
  • Chronic Exposure: Prolonged exposure to Mancozeb has been linked to thyroid toxicity and is classified as a possible human carcinogen (Coccu, 2022) due to the ethylene thiourea (ETU) breakdown product. ETU is also considered a potential endocrine disruptor. 
  • Residue Risks: Although Mancozeb is not absorbed by plants, residues on treated crops can pose health risks if consumed without adequate washing or peeling.
• Environmental Impact:
  • Mancozeb is toxic to aquatic organisms and can persist in the soil. Its widespread use may contribute to soil contamination and negatively affect beneficial organisms.
  • As a non-systemic fungicide, it washes off with rainfall, leading to potential waterway contamination.

Safe Usage and Alternatives

To mitigate risks:

• Proper PPE (Personal Protective Equipment): Always wear gloves, masks, and protective clothing during application.
• Pre-Harvest Interval (PHI): Strictly adhere to the recommended waiting period between Mancozeb application and crop harvest.
• Integrated Pest Management (IPM): Use alternatives like biological controls, resistant crop varieties, or other systemic fungicides with lower environmental footprints.

In areas where Mancozeb is banned, alternative fungicides such as chlorothalonil, propiconazole, or biofungicides like Trichoderma species may be used, though they vary in effectiveness.

One other benefit is that the manganese and zinc in the compound strengthen the fruit too which increases crop yield and thus improves the economic benefits of produce production (Thind & Hollomon, 2018).

References

Cocco, P. (2022). Time for re-evaluating the human carcinogenicity of ethylenedithiocarbamate fungicides? A systematic review. International Journal of Environmental Research and Public Health, 19(5), 2632 (Article).

Lentza-Rizos, C. (1990). Ethylenethiourea (ETU) in relation to use of ethylene bisdithiocarbamate (EBDC)fungicides. Reviews of Environmental Contamination and Toxicology 115 pp. 1-37 

Petha, N. H., Lokhande, R. S., Seshadri, D. T., Patil, R. M., Bhagat, T. S., & Patil, J. G. (2017). A simple pre-column derivatization method for the determination of mancozeb technical (fungicide) by reverse phase HPLC-UV. Analytical Methods, 9(32), pp. 4702-4708.

Thind, T. S., & Hollomon, D. W. (2018). Thiocarbamate fungicides: reliable tools in resistance management and future outlook. Pest Management Science, 74(7), pp. 1547-1551 (Article).