The efficacy of triazoles lies in their specific mode of action. They target the biosynthesis of ergosterol, a critical component of fungal cell membranes. Specifically, triazoles inhibit the enzyme CYP51 (lanosterol 14-alpha-demethylase). By blocking this enzyme, the fungicide prevents the conversion of lanosterol to ergosterol. The resulting depletion of ergosterol disrupts the cell membrane's structure and function, leading to increased permeability and, ultimately, the cessation of fungal growth. Unlike contact fungicides, triazoles are systemic; they are absorbed by the plant and can move translaminarly (through the leaf) or via the xylem, offering protection for new growth and curative activity on existing infections.
| Risk | Explanation | |------|-------------| | | Triazoles can stunt young plants, reduce internode length, and cause leaf distortion—sometimes used intentionally in turf but undesirable in vegetables. | | Resistance | High to very high resistance risk. Many fungi have developed target-site mutations (CYP51 alterations). | | Reproductive Toxicity | Some triazoles are suspected endocrine disruptors (e.g., tebuconazole, propiconazole). Handle with PPE. | | Phytotoxicity | Certain crops (e.g., cherries, some apple varieties) are sensitive. Temperature inversions increase injury risk. | triazole fungicides