Dimethomorph

Vapor pressure kPa: 1 x 10-6 Pa (25 ° C)

Water solubility: 50 mg l-1 (20-23 ° C)

Mainly used to control grape downy mildew and potato late blight, usually mixed with mancozeb

Dimethomorph is a systemic fungicide used primarily in the control of oomycete fungi, which are responsible for several significant plant diseases. It is widely applied in agriculture to protect a variety of crops, including potatoes, tomatoes, grapes, and cucurbits, from diseases like late blight, downy mildew, and other water molds. Dimethomorph belongs to the chemical class of morpholine fungicides and works by inhibiting fungal cell wall synthesis, making it an effective tool in integrated disease management strategies.

Key Features

1. Chemical Class: Morpholine

2. Mode of Action: Dimethomorph inhibits the synthesis of the fungal cell wall by interfering with the production of sterols, which are essential for cell membrane integrity. This leads to cell wall breakdown and fungal death.

3. Formulations: Available in various formulations, including wettable powders (WP), suspension concentrates (SC), and emulsifiable concentrates (EC).

4. Target Pathogens: Effective against several oomycete fungi, including Phytophthora, Pythium, and Peronospora species.

Applications

Crops

• Potatoes: Controls late blight (Phytophthora infestans), a major threat to potato crops.

• Tomatoes: Prevents downy mildew (Peronospora destructor).

• Grapes: Used to manage downy mildew (Plasmopara viticola), which affects grapevines.

• Cucurbits: Controls diseases like downy mildew and other fungal infections.

• Other Crops: Dimethomorph can also be used on a variety of other vegetables and ornamental plants to protect against oomycete diseases.

Target Diseases

• Late Blight: Caused by Phytophthora infestans, particularly in potatoes and tomatoes.

• Downy Mildew: Caused by various Peronospora and Plasmopara species, affecting crops like cucumbers, grapes, and lettuce.

• Pythium Rot: Affects roots and seedlings of various crops, particularly in waterlogged conditions.

Mode of Action

Dimethomorph works by disrupting the synthesis of sterols in the fungal cell membrane, which is essential for cell wall integrity. This interference with cell wall formation weakens the fungus, preventing its growth and reproduction. Since it is systemic, Dimethomorph is absorbed by the plant and moves through the tissues, offering protection even in new growth areas. This makes it particularly effective for preventing the spread of infections in plants.

Advantages

1. Effective Against Oomycetes: Dimethomorph is particularly effective against oomycete fungi, which are responsible for some of the most destructive plant diseases.

2. Systemic Action: Its systemic nature ensures that it provides long-lasting protection, even in new growth areas of the plant.

3. Broad Spectrum: Dimethomorph controls a wide range of diseases caused by oomycetes, making it versatile for various crops.

4. Low Toxicity to Non-Target Organisms: Dimethomorph has relatively low toxicity to non-target organisms when used according to label instructions.

5. Resistance Management: It is an effective component in resistance management programs, particularly when used in rotation with fungicides from different chemical classes.

Usage Guidelines

1. Application Timing:

   • Pre-Harvest: Dimethomorph is typically applied before the onset of disease symptoms, especially during periods of high humidity or rainfall when fungal infections are more likely.

   • Post-Harvest: It is not commonly used post-harvest but may be applied to plants in storage if necessary.

   
   

2. Dosage: The recommended application rate varies depending on the crop and disease severity. Typical application rates range from 100 to 400 g/ha.

3. Spray Coverage: Ensure thorough coverage of the plant foliage, especially on the undersides of leaves where fungal spores are likely to germinate.

4. Reapplication Interval: Dimethomorph has a relatively long residual activity, but it may need to be reapplied every 7–14 days, depending on environmental conditions and disease pressure.

Safety and Environmental Considerations

Handling and Storage

• Protective Measures: Wear appropriate personal protective equipment (PPE), such as gloves, goggles, and protective clothing, when handling Dimethomorph.

• Storage: Store in a cool, dry place, away from food, feed, and water sources. Keep containers tightly sealed to avoid contamination.

Environmental Impact

• Aquatic Toxicity: Dimethomorph is toxic to aquatic organisms, so care should be taken to avoid runoff into water bodies.

• Soil Persistence: It has moderate persistence in soil, so it is important to follow application guidelines to minimize environmental impact.

• Non-Target Organisms: It is generally safe for beneficial insects when used as directed, but care should be taken to avoid exposure to bees and other pollinators during application.

Human Health Risks

• Toxicity: Dimethomorph is of low toxicity to humans when used according to label instructions. However, it is important to avoid inhalation or skin contact.

• First Aid:

  • Skin Contact: Wash with soap and water immediately.

  • Eye Contact: Rinse thoroughly with water for at least 15 minutes.

  • Inhalation: Move to fresh air and seek medical attention if symptoms persist.

  
  

Resistance Management

To reduce the risk of resistance, it is recommended to rotate Dimethomorph with fungicides from different chemical classes. Overuse of any single fungicide can lead to resistance, reducing its effectiveness over time.

Limitations

1. Resistance Risk: Dimethomorph, like all fungicides, can lead to resistance if overused or applied in high concentrations.

2. Rainfastness: Dimethomorph is rainfast after approximately 1–2 hours of application, so reapplication may be necessary after heavy rainfall.

3. Limited Efficacy Against Other Pathogens: While Dimethomorph is highly effective against oomycetes, it does not control other types of fungi, such as Ascomycetes or Basidiomycetes.

Conclusion

Dimethomorph is a highly effective systemic fungicide used to control a wide range of oomycete pathogens, including late blight and downy mildew, in various crops. Its ability to prevent the growth of fungal pathogens through its action on sterol biosynthesis makes it a key tool in integrated disease management programs. By following recommended usage guidelines and incorporating resistance management practices, Dimethomorph can help protect crops and ensure healthy yields.