What Is Dimethomorph and Why Is It a Key Fungicide Against Oomycetes?

Technical Introduction

Dimethomorph is a systemic, selective fungicide belonging to the morpholine chemical class. It is highly effective against Oomycete fungi such as Phytophthora spp. and Plasmopara spp., which cause devastating diseases like downy mildews, late blight, and root rots.

Its mode of action is unique: Dimethomorph inhibits cell wall formation in Oomycetes by interfering with the synthesis of cellulose and other structural components. This disrupts spore germination, mycelial growth, and sporulation, ultimately preventing pathogen development.

Unlike many fungicides, Dimethomorph provides protective, curative, and antisporulant activity, making it an essential component in modern fungicide programs.

Applications

• Potatoes & Tomatoes:

  • Controls late blight (Phytophthora infestans).

  • Used in rotation or mixture with contact fungicides (e.g., mancozeb, chlorothalonil).

• Grapes:

  • Highly effective against downy mildew (Plasmopara viticola).

  • Commonly applied in tank mixtures with folpet, dithianon, or mancozeb.

• Vegetables (Cucurbits, Lettuce, Onions):

  • Protects against downy mildew and damping-off diseases.

• Tropical Crops (Cocoa, Citrus, Pineapple):

  • Effective against Phytophthora pod rot and root rot.

• Ornamentals & Turf:

  • Used against Pythium root rot and damping-off diseases in nurseries and golf courses.

Advantages

• Highly Specific to Oomycetes: Excellent performance against Phytophthora, Pythium, and Plasmopara.

• Systemic & Translaminar: Moves inside plant tissues, protecting new growth.

• Multiple Modes of Protection: Preventive, curative, and antisporulant activity.

• Resistance Management Role: Often used in mixtures with multi-site fungicides (e.g., mancozeb, copper) or with other systemic fungicides (e.g., cymoxanil).

• Crop Safety: Well tolerated on a wide range of crops.

• Residue Stability: Provides long-lasting disease protection.

Specifications (Typical Parameters)

FAQ

Q1: What is Dimethomorph mainly used for?
A: It is primarily used against Oomycete diseases such as late blight (Phytophthora infestans) and downy mildew (Plasmopara viticola).

Q2: Is Dimethomorph systemic?
A: Yes, it is systemic and translaminar, protecting treated and new plant growth.

Q3: Does Dimethomorph control non-Oomycete fungi?
A: No, its spectrum is narrow and specific to Oomycetes. For broad-spectrum control, it must be mixed with other fungicides.

Q4: How is Dimethomorph applied?
A: Usually as a foliar spray in combination with protectant fungicides (e.g., mancozeb, copper).

Q5: Can pathogens develop resistance to Dimethomorph?
A: Yes, resistance risk exists due to its single-site mode of action. Best practice is to use it in rotation or mixtures with fungicides of different FRAC groups.