Chapter 13: Fungicides: Several Generations and More Needed

The second generation brought organic compounds including organomercurials, organotin formulations, and safer alternatives such as dithiocarbamates and phthalimides that provided broader protection in agricultural settings while introducing concerns about toxic byproducts and environmental persistence. The third generation marked a fundamental shift toward systemic fungicides beginning with benzimidazoles, which penetrated plant tissues and disrupted fungal nuclear division, followed by sterol inhibitors that targeted ergosterol biosynthesis across diverse fungal orders, and ambimobile compounds like mefenoxam that proved particularly effective against oomycete pathogens such as Phytophthora and Pythium despite rapid resistance development. The unexpected fourth generation, the strobilurins, emerged from natural compounds found in mushroom species and synthetic derivatives like azoxystrobin became globally dominant through their novel mechanism of blocking mitochondrial respiration at the cytochrome bc1 complex, combining protectant, systemic, and eradicant properties while simultaneously creating new resistance challenges. The chapter emphasizes the critical problem of fungicide resistance, illustrated through examples like Benomyl resistance appearing within two years of widespread adoption, leading to the development of the Fungicide Resistance Action Committee system for grouping products by mechanism of action to guide strategic rotations. Modern fungicide management now integrates biological alternatives like Bacillus subtilis formulations with cultural practices, cultivar selection, and sanitation within comprehensive integrated pest management frameworks, reflecting the ongoing tension between fungal adaptability and the need for increasingly sophisticated and judicious chemical interventions.