Mode of action and target site or mechanism of action:
Mode of action (MOA) describes the biochemical processes by which the fungicide poisons the fungus (for example, disrupting cell wall synthesis). Target site of action or mechanism of action is the exact location of inhibition, such as interfering with the activity of a specific enzyme within a metabolic pathway.
Selection and selection pressure:
Selection is the process by which control measures favor resistant individuals over susceptible ones (see Understanding Resistance). Selection pressure refers to the intensity of the selection.
Protectant or Penetrant Fungicide:
Protectant fungicides are active on plant surfaces where they form a chemical barrier between the plant and fungus. There is no movement of the fungicide into the plant. Protectant fungicides must be applied prior to infection and re-applied to new growth if conditions remain favorable for disease development. Penetrant (also known as “site-specific”) fungicides are absorbed into plants following application and also function as a protectant fungicide at the site of contact. They are generally considered systemic fungicides, but they have different degrees of systemic movement:
Locally systemic fungicides move only a short distance such as within the leaf to which it is applied.
Translaminar fungicides move through the leaf from one side to the other.
Xylem mobile fungicides move upward in plants and outward to the periphery of leaves with water through the xylem, the water conducting tissue of the plant. This is known as acropetal movement
Amphimobile/truly systemic fungicides move both upward through the xylem, and downward through the phloem, the food conducting tissue of the plant. These fungicides are described as amphimobile. Few fungicides are fully systemic.
Compiled by Dr. Wayne Buhler, PhD
Topics Included in this Module
- Fungicide Terms to Know — Understand the terms that describe fungicide activity and resistance development
- Is Resistance to Blame? — Most fungicide failures are not likely due to resistance.
- Mechanisms of Fungicide Resistance — There are several ways that populations of fungi become resistant.
- Raised Resistance Risks — The fungicide mode of action can determine the likelihood and speed of resistance development
- Proactive Fungicide Resistance Avoidance — Use diverse disease control tactics to help avoid resistance.
- Spraying by the Numbers — Fungicides with similar modes of action could exhibit cross resistance. One way to avoid this is by rotating chemically dissimilar fungicides.
- How to Manage Fungicide Resistance — If fungicide resistance is confirmed or highly suspected, diverse approaches to managing resistance need to be incorporated
- Resources and Suggested Reading