Fungicide Terms to Know
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 (above) move through the leaf from one side to the other.
(Disease Management Strategies-Purdue Extension) |
Xylem mobile fungicides (below) 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
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Amphimobile/truly systemic fungicides (above) 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
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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. |
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