Evaluation of oomycete-targeted fungicides for controlling downy mildew in vegetable crops

Currently, 56 distinct fungicide modes of action are recognized and classified by the Fungicide Resistance Action Committee (FRAC), including compounds with unknown mechanisms. This diversity supports effective resistance management. However, the availability of fungicides is often limited by regional registration and economic factors, restricting their use in certain crops. Consequently, key crop–pathogen systems may have few control options. Furthermore, many fungicides exhibit a narrow spectrum of activity, with a large proportion targeting specific pathogen groups such as oomycetes or even single species. Oomycetes are phylogenetically distinct from true fungi such as phytopathogenic Deuteromycetes, Ascomycetes, and Basidiomycetes, exhibiting significant biological and biochemical differences that influence their sensitivity to fungicidal compounds.