6/27/2025

Corn Foliar Fungicide Modes of Action

Fungicide Application Timing in Corn

Crop Focus
Written by Mark Jeschke, Ph.D., Pioneer Agronomy Manager

Key Points

  • Many newer foliar fungicide products for corn have 2 or 3 active ingredients with different target sites.
  • Target site is the basis for FRAC codes, which are group numbers assigned by the Fungicide Resistance Action Committee that are shown on fungicide product labels. In practice, the term “mode of action” is often used interchangeably with target site or FRAC group.
  • Fungicides with multiple modes of action can provide more effective disease control and reduce selection for resistance in pathogens.

Fungicide Mode of Action

  • Older fungicides typically only had one active ingredient, but many newer ones have two, or even three, active ingredients with different target sites.
  • Fungicide mode of action (MOA) refers to the cellular process inhibited by a fungicide.
  • Fungicide target site (or site of action) refers to the specific enzyme involved in a cellular process to which a fungicide binds. It is possible for two fungicides to have the same mode of action but different target sites.
  • Target site is the basis for FRAC codes, which are group numbers assigned by the Fungicide Resistance Action Committee that are shown on fungicide product labels.
  • In practice, the term “mode of action” is commonly used interchangeably with target site or FRAC group.
  • FRAC currently recognizes 12 different known fungicide modes of action. Of these, two are currently utilized in foliar fungicide products used in corn: inhibition of cellular respiration or inhibition of sterol biosynthesis in cell membranes.
  • This includes three different FRAC groups (target sites), two of which share the same mode of action:
    • Group 3: Demethylation Inhibitors (DMI)
    • Group 7: Succinate Dehydrogenase Inhibitors (SDHI)
    • Group 11: Quinone Outside Inhibitors (QoI)

Multiple Mode of Action Fungicides

  • One of the most important benefits of fungicide products with multiple modes of action is pathogen resistance management.
  • Fungicides with multiple modes of action can also provide more effective disease control by targeting a broader range of fungal diseases and pathogens and providing more comprehensive protection for the corn crop. 

Group 3: Demethylation Inhibitors

Mode of Action: Sterol biosynthesis in membranes

Target Site: C14-demethylase in sterol biosynthesis

Mobility: Xylem-mobile

Resistance Risk: Medium

  • Group 3 fungicides are referred to as the triazoles, as most of the active ingredients used in corn are in this chemical group.
  • These fungicides are effective against many fungal diseases, especially rusts and leaf spots.
  • Many current fungicides combine a DMI with a Group 11 fungicide (strobilurin), as well as three-way products that also include a Group 7 fungicide.
  • DMI fungicides are locally systemic and xylem-mobile, which means they can spread in the leaf tissue from the site of application and move upward in the plant via the xylem tissue.
  • These fungicides typically have around 14 days of residual activity after application.

Group 7: Succinate Dehydrogenase Inhibitors

Mode of Action: Cellular respiration

Target Site: Complex II: succinate-dehydrogenase

Mobility: Locally systemic

Resistance Risk: Medium-high

  • The first generation of these fungicides had relatively limited disease spectra. SDHI fungicides with increased spectrum and potency were commercialized beginning in the early 2000s.
  • Corn fungicide products that include a SDHI typically also include a Group 3 or Group 11 fungicide, or both.
  • SDHI fungicides are locally systemic, capable of moving a short distance from the site of application.
  • SDHIs have longer residual activity than other groups.

Group 11 Quinone Outside Inhibitors

Mode of Action: Cellular respiration

Target Site: Complex III: cytochrome bc1

Mobility: Locally systemic / translaminar, some are xylem-mobile

Resistance Risk: High

  • The QoI fungicides, commonly known as strobilurins, are a relatively new group of fungicides modeled after a naturally occurring fungicidal compound.
  • QoI fungicides are active against a broad range of plant pathogens. Most have locally systemic and translaminar mobility in plants, and some are also xylem mobile.
  • These fungicides can have 7-21 days of residual activity.

Table 1. Active Ingredients (%) by FRAC Group

Table 1. Active ingredients (%) by FRAC group of foliar fungicides labelled for use in corn (Wise et al., 2025). Click here or on the image below for a larger view.

Active ingredients - percent - by FRAC group of foliar fungicides labelled for use in corn

Reference.: Wise, K. 2025. Fungicide Efficacy for Control of Corn Foliar Disease. Crop Protection Network CPN-2011-W.



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