Fungicide Application Timing

The key to preventing ASR damage is effective scouting and timely use of fungicide control. Here is a basic overview of fungicides.

Quick Tips – Fungicide Basics

Fungicides can be classified by their general function (preventative or curative), mobility in the plant (contact, fixed protectant, penetrant or systemic) and mode of action or chemistry.

Three families of fungicide compounds:

• Chloronitriles -- Active against spore germination. Is classified as a protectant. Remain on leafs surface to deter the rust as a contact fungicide. Residual activity -- up to 7 days
• Strobilurines -- Blocks fungal germ tubes from penetrating leaf, but not effective once infection has taken place. Absorbs and moves through the leaf to form a barrier. Residual activity – up to 14 days
• Triazoles -- Only curative fungicide that will kill active ASR infestation, plus provide preventative control. Residual activity – up to 21 days.

To increase fungicide effectiveness, growers should select the fungicide with the highest level of control and apply before disease pressure is too severe.

Following treatment:

• After treatment, scout again as the lifespan of the fungicide ends.
• Determine effectiveness of treatment:
  • Dead spores: Black spots on the leaf
  • New spores: Red, brown, or tan on the leaf

More information:

Using Fungicides to Manage Soybean Rust Manual