What Is Metalaxyl and Why Is It a Key Fungicide Against Oomycete Diseases?

Technical Introduction

Metalaxyl is a systemic phenylamide fungicide developed for the control of Oomycete pathogens. It is particularly effective against species of Phytophthora, Pythium, Peronospora, and Plasmopara, which cause destructive diseases such as downy mildews, late blight, and damping-off.

The mode of action of Metalaxyl is unique: it inhibits RNA polymerase I activity in Oomycetes, preventing ribosomal RNA synthesis. This disruption blocks mycelial growth, sporangia formation, and spore germination, ultimately halting disease development.

Due to its systemic nature, Metalaxyl provides both protective and curative activity, making it one of the most widely used fungicides in plant protection programs.

Applications

• Potatoes & Tomatoes:

  • Controls late blight (Phytophthora infestans), often in combination with protectant fungicides such as mancozeb or chlorothalonil.

• Grapes:

  • Used against downy mildew (Plasmopara viticola), often as part of resistance management strategies.

• Vegetables (Onions, Cucurbits, Lettuce, Peas):

  • Effective against downy mildew and damping-off diseases.

• Cereals (Wheat, Barley):

  • Used as a seed treatment against Pythium spp. causing root rot and damping-off.

• Tropical Crops (Cocoa, Coffee, Pineapple, Citrus):

  • Controls Phytophthora pod rot, root rot, and gummosis.

• Ornamentals & Turf:

  • Protects against Pythium and Phytophthora root rots in nurseries and golf courses.

Advantages

• Systemic Action: Rapidly absorbed and translocated within plants (both xylem and phloem).

• Preventive & Curative: Works at early infection stages and provides post-infection control.

• Highly Effective on Oomycetes: One of the most reliable fungicides for Phytophthora, Pythium, and Plasmopara.

• Flexible Application Methods: Foliar sprays, soil drenches, drip irrigation, seed treatments, and trunk injections.

• Crop Safety: Well tolerated on a wide range of crops when used as directed.

• Synergistic in Mixtures: Often combined with contact fungicides to broaden spectrum and delay resistance.

Specifications (Typical Parameters)

FAQ

Q1: What crops benefit most from Metalaxyl?
A: Potatoes, tomatoes, grapes, cereals, citrus, cocoa, pineapple, and ornamentals.

Q2: Is Metalaxyl systemic?
A: Yes, it is fully systemic, moving upward and downward in plant vascular tissues.

Q3: Does Metalaxyl control non-Oomycete fungi?
A: No, it is specific to Oomycetes and must be mixed with broad-spectrum fungicides for wider disease coverage.

Q4: Can pathogens develop resistance to Metalaxyl?
A: Yes, resistance has been reported in Phytophthora infestans and Plasmopara viticola. To manage this, it should always be used in mixtures or rotations with fungicides of different FRAC groups.

Q5: How is Metalaxyl typically applied?
A: As foliar sprays, soil drenches, seed treatments, or trunk injections, depending on the crop and disease target.