8% Oxadixyl + 56% Mancozeb WP: A Potent Broad – Spectrum Fungicide for Crop Protection

Active Ingredients and Their Chemical Properties

2.1 Oxadixyl

• Chemical Name: 2 – methoxy – N – (2 – oxo – 1,3 – oxazolidin – 3 – yl) acet – 2′,6′ – xylidide
• CAS Number: 77732 – 09 – 3
• Molecular Formula: C₁₄H₁₈N₂O₄
• Molecular Weight: 278.3 g/mol
• Properties: Oxadixyl is a systemic fungicide. It has some solubility in water, which is crucial for its uptake by plants. In the 8% Oxadixyl + 56% Mancozeb WP formulation, oxadixyl is present in a finely powdered form within the wettable powder matrix. It is relatively stable under normal storage conditions but can degrade under extreme heat, moisture, or in the presence of strong acids or alkalis.

2.2 Mancozeb

• Chemical Name: Manganese ethylene bis(dithiocarbamate) (polymeric) complex with zinc salt
• CAS Number: 8018 – 01 – 7 (also formerly 8065 – 67 – 6)
• Molecular Formula: (C₄H₆MnN₂S₄)ₓ(Zn)ᵧ
• Properties: Mancozeb is a non – systemic, broad – spectrum contact fungicide. It has a low solubility in water, but the wettable powder formulation ensures its effective dispersion in water for spraying. Mancozeb is known for its stability in the formulation and has a characteristic off – white to light – tan color in its pure form. In the 8% Oxadixyl + 56% Mancozeb WP, it forms a significant portion of the powder, contributing to the overall fungicidal activity.

3. Mode of Action

3.1 Oxadixyl

• Inhibition of Protein Synthesis: Oxadixyl is believed to inhibit protein synthesis in fungi. It interferes with the synthesis of ribosomal RNA, which is essential for the translation process in fungal cells. As a result, the production of vital proteins required for fungal growth, development, and reproduction is disrupted.
• Systemic Activity: Oxadixyl exhibits systemic properties. When applied to the soil or foliage, it can be absorbed by the plant’s roots or leaves, respectively. Once inside the plant, it translocates acropetally (upward) within the plant’s vascular system. This systemic movement allows it to reach parts of the plant that may not have been directly sprayed, providing protection against fungal infections in new growth areas. It also has some translaminar movement, meaning it can move across leaf tissues, further enhancing its protective and curative capabilities.

3.2 Mancozeb

• Barrier Formation and Enzyme Inhibition: Mancozeb functions primarily as a protective fungicide. When applied to the plant surface, it forms a thin, protective film. This film acts as a physical barrier, preventing fungal spores from coming into contact with the plant tissue. Additionally, mancozeb releases manganese and zinc ions, along with the dithiocarbamate moiety. These ions and the dithiocarbamate can inhibit several key enzymes in the fungal metabolism. For example, they can interfere with the enzymes involved in the synthesis of fungal cell membranes and the metabolism of lipids, ultimately leading to the death of the fungal cells.
• Multi – Site Activity: Unlike some fungicides that target a single site in the fungal cell, mancozeb has multi – site activity. This reduces the likelihood of fungi developing resistance to it, as multiple metabolic pathways need to be altered simultaneously for the fungus to become resistant.

3.3 Synergistic Effect

4. Target Crops and Diseases

4.1 Target Crops

• Fruit Crops:
  • Grapes: Widely used in vineyards to protect grapevines from diseases such as downy mildew (Plasmopara viticola), which can cause yellowish – green lesions on the upper leaf surface and a white, downy growth on the lower surface. It also helps control grapevine blight diseases, ensuring healthy grape production and preventing post – harvest losses.
  • Strawberries: Protects strawberry plants from diseases like red stele root rot (Phytophthora fragariae), which can cause stunted growth, wilting, and death of the plants. By preventing these diseases, it helps in maintaining the quality and yield of strawberries.
  • Citrus Fruits: Effective in controlling diseases such as citrus canker (Xanthomonas citri subsp. citri), although this is a bacterial disease, the fungicide can help manage secondary fungal infections that may occur in the damaged areas. It also protects against fungal diseases like citrus scab (Elsinoe fawcettii), which can cause rough, scabby lesions on the fruit and leaves.
• Vegetable Crops:
  • Tomatoes: Used to manage diseases like early blight (Alternaria solani), which causes dark, concentric – ringed lesions on the leaves, and late blight (Phytophthora infestans), a devastating disease that can rapidly destroy tomato plants. In tomatoes, 8% Oxadixyl + 56% Mancozeb WP can be applied at various stages of growth to protect the plants from these diseases.
  • Cucurbits (Cucumbers, Melons, Squash): Highly effective against diseases such as cucumber downy mildew (Pseudoperonospora cubensis), which is a common and destructive disease in cucurbits. It appears as yellow, angular lesions on the upper leaf surface with a grayish – purple downy growth on the lower surface. The fungicide also helps control anthracnose (Colletotrichum spp.) in cucurbits, preventing the formation of sunken, black lesions on the fruits.
  • Leafy Greens (Lettuce, Spinach): Protects these crops from diseases like downy mildew (Bremia lactucae in lettuce), which can cause yellowing and browning of the leaves, and Botrytis rot (Botrytis cinerea). In lettuce, for example, the fungicide application helps in maintaining the freshness and quality of the leaves, which are highly perishable.
• Field Crops:
  • Cereals (Wheat, Barley, Oats): Used to control diseases such as wheat downy mildew (Sclerophthora macrospora), which can cause stunted growth and reduced yields. It also has some activity against leaf rust (Puccinia recondita) in wheat, which appears as small, orange – brown pustules on the leaves.
  • Oilseed Rape: Effective in managing diseases like Sclerotinia stem rot (Sclerotinia sclerotiorum), which can cause lodging and reduced seed yield. The fungicide application helps in protecting the stems and pods of oilseed rape plants, ensuring better crop productivity.
  • Potatoes: Helps control potato late blight (Phytophthora infestans), a well – known and destructive disease that can cause significant losses in potato production. By preventing the spread of the disease, it helps in maintaining the quality and quantity of potato tubers.
• Ornamental Plants:
  • Roses: Protects roses from diseases like downy mildew (Peronospora sparsa), which can cause purple – brown spots on the leaves and a white, downy growth on the undersides. It also helps in controlling black spot (Diplocarpon rosae), which appears as black spots on the leaves, maintaining the aesthetic value of roses in gardens and landscapes.
  • Chrysanthemums: Used to manage diseases such as downy mildew (Peronospora chrysanthemi) and Botrytis blight (Botrytis cinerea). In chrysanthemums, the fungicide can prevent the development of these diseases, ensuring the production of high – quality flowers for the cut – flower industry or garden display.

4.2 Target Diseases

• Downy Mildew: Caused by various species of Peronosporaceae, downy mildew is a common and destructive disease across many crops. The 8% Oxadixyl + 56% Mancozeb WP is highly effective in preventing and controlling downy mildew. Oxadixyl’s systemic action helps in controlling the fungus within the plant, while mancozeb’s protective film on the plant surface prevents the germination of fungal spores.
• Late Blight: In crops like tomatoes and potatoes, late blight (Phytophthora infestans) is a major concern. The combination of oxadixyl and mancozeb can effectively manage late blight. Oxadixyl can penetrate the plant tissues and inhibit the growth of the fungus, while mancozeb’s multi – site action on the plant surface helps in preventing the spread of the disease.
• Anthracnose: Caused by Colletotrichum spp., anthracnose affects a wide range of crops, causing dark, sunken lesions on fruits, leaves, and stems. The fungicide’s components work together to control anthracnose. Mancozeb’s protective action on the plant surface stops the initial infection, and oxadixyl’s systemic activity helps in controlling the fungus if it has already penetrated the plant.
• Leaf Spot Diseases: There are numerous leaf spot diseases caused by different fungal pathogens, such as Alternaria spp. and Cercospora spp. These diseases cause the formation of spots on the leaves, which can lead to defoliation if left uncontrolled. 8% Oxadixyl + 56% Mancozeb WP can effectively control leaf spot diseases. Mancozeb’s barrier on the leaf surface and its enzyme – inhibiting action prevent the spread of the fungus, while oxadixyl’s systemic properties help in treating the infection if it has already occurred.

5. Dosage and Application Guide

5.1 Dosage Recommendations

• General Guidelines: The recommended dosage of 8% Oxadixyl + 56% Mancozeb WP varies depending on the crop, the target disease, and the stage of crop growth. As a general rule, for foliar applications, the dosage typically ranges from 1200 – 1500 g/ha. However, for specific crops and diseases, the dosage may be adjusted. For example, in controlling cucumber downy mildew, a dosage of 1200 – 1300 g/ha may be used, while for controlling potato late blight, a slightly higher dosage of 1300 – 1500 g/ha may be recommended.
• Crop – Specific Dosages:
  • Fruit Crops:
    • Grapes: For controlling downy mildew in grapes, an application rate of 1300 – 1400 g/ha may be used. This is usually applied in a sufficient volume of water (e.g., 500 – 1000 liters/ha) to ensure thorough coverage of the grapevine leaves, including the upper and lower surfaces.
    • Strawberries: To protect against red stele root rot, a dosage of 1200 – 1300 g/ha can be applied. The application may be done as a soil drench or a foliar spray, depending on the stage of the disease and the growth stage of the strawberry plants.
  • Vegetable Crops:
    • Tomatoes: For managing early blight, a dosage of 1250 – 1350 g/ha may be used. It is advisable to start the application at the first sign of disease symptoms and repeat at 7 – 10 – day intervals, depending on the disease pressure. For late blight, a higher dosage within the recommended range may be required.
    • Cucumbers: To control downy mildew in cucumbers, 1200 – 1250 g/ha can be applied. The spray should be directed to cover the entire cucumber plant, focusing on the leaves where the disease usually starts.
  • Field Crops:
    • Cereals: In wheat, for the control of downy mildew, 1200 – 1300 g/ha may be applied. The first application is usually made when the first symptoms appear on the lower leaves, and subsequent applications may be done at 10 – 14 – day intervals.
    • Potatoes: To manage late blight in potatoes, a dosage of 1300 – 1500 g/ha can be used. The application is typically started at the early stages of the disease, and the frequency of application may be increased during periods of high disease pressure.

5.2 Application Timing

• Preventive Applications: It is highly recommended to apply 8% Oxadixyl + 56% Mancozeb WP preventively, before the onset of fungal diseases. This is especially crucial in areas with a history of fungal problems or during periods when environmental conditions (such as high humidity, warm temperatures, and poor air circulation) are favorable for fungal growth. For example, in vineyards, applications can be made before the rainy season or when the humidity levels start to rise, as these conditions are conducive to the development of downy mildew. By applying the fungicide preventively, a protective barrier is formed on the plant surface, and the systemic oxadixyl is already present in the plant to combat any potential infections.
• Curative Applications: If fungal symptoms are already present, applications should be made as soon as possible. However, the effectiveness of curative applications may be slightly lower than preventive ones. In the case of late blight on potatoes, if the disease is detected early, a timely application of 8% Oxadixyl + 56% Mancozeb WP can still prevent significant damage. Curative applications work by the systemic oxadixyl inhibiting the further growth of the established fungal infection within the plant, while mancozeb helps in preventing the spread of the fungus from the infected areas to the healthy parts of the plant.

5.3 Application Methods

• Foliar Spray: The most common method of applying 8% Oxadixyl + 56% Mancozeb WP is through foliar spraying. First, the required amount of the wettable powder should be measured accurately and added to a clean spray tank. Then, it should be thoroughly mixed with the appropriate volume of water according to the recommended dosage. Use a calibrated sprayer to ensure an even distribution of the spray solution. For best results, spray the entire plant, including the upper and lower surfaces of leaves, stems, and fruits. In large – scale agricultural operations, ground – based sprayers equipped with appropriate nozzles (such as flat – fan nozzles for even coverage) may be used. In small – scale horticulture or home gardening, handheld sprayers can also be effective. It is important to note that the spray should be done on a calm day to avoid drift, which can lead to off – target application and reduced efficacy.
• Soil Drench: In some cases, especially for controlling soil – borne diseases like red stele root rot in strawberries, 8% Oxadixyl + 56% Mancozeb WP can be applied as a soil drench. This involves diluting the wettable powder in a large volume of water and applying the solution directly to the soil around the plant roots. The dosage and volume of the soil drench depend on the type of crop, the size of the plants, and the severity of the soil – borne disease. For example, in treating red stele root rot in strawberry plants, a soil drench with 8% Oxadixyl + 56% Mancozeb WP at a specific concentration may be applied to the root zone to inhibit the growth of the Phytophthora fungus in the soil.
• Seed Treatment: Although less common for this particular formulation, in certain situations, 8% Oxadixyl + 56% Mancozeb WP can be used for seed treatment. This involves coating the seeds with a suspension of the fungicide before sowing. Seed treatment can protect the emerging seedlings from soil – borne and seed – borne fungal diseases, providing an early start to a healthy crop. The seeds are usually treated by soaking them in a diluted solution of the wettable powder for a specific period (e.g., 10 – 30 minutes, depending on the crop and the recommended protocol) and then drying them before sowing. This method helps in preventing diseases that could affect the germination and early growth of the seedlings.

6. Safety and Environmental Considerations

6.1 Toxicity to Humans and Animals

• Low Mammalian Toxicity: 8% Oxadixyl + 56% Mancozeb WP is generally considered to have low mammalian toxicity. However, as with any pesticide, it is important to handle it with care. When applying the fungicide, users should wear appropriate personal protective equipment (PPE), such as gloves, goggles, and a mask, to avoid skin contact, eye exposure, and inhalation of the powder or spray mist. In case of accidental ingestion, seek medical attention immediately.
• Impact on Non – Target Organisms: While the fungicide is primarily designed to target fungi, it may have some impact on non – target organisms. For example, it is important to avoid spraying near beneficial insects such as bees, as they can be affected by the fungicide. Although the toxicity to honey bees is relatively low for mancozeb, oxadixyl may have some effects, and the combined formulation should be used with caution