Fungicides are essential for maintaining healthy crops, and consistent yields of high quality produce. This is unlikely to change in the foreseeable future. Protectant fungicides prevent infection, are phytotoxic so remain on leaf surfaces protecting only foliage existing when treatments are applied. Eradicant (curative) fungicides control existing infections, are not phytotoxic and xylem mobile so protect new foliage appearing after treatment. Protectant fungicides are usually multi-site inhibitors whereas eradicants only inhibit one step in a metabolic pathway. A major constraint is loss of fungicides through resistance. Mixtures or alternation of low-risk multi-site inhibitors and high-risk single-site inhibitors underpins resistance management strategies. Examples are given for modes of action and resistance mechanisms for key active ingredients. Fungicide chemistry has provided increasingly active, but environmentally safe, compounds allowing lower dose rates. This trend is likely to continue through inhibition of regulatory rather than metabolic pathways.

Key concepts:

• Differences between protectant and eradicant fungicides.
  
• Differences between multi-site and single-site inhibitors.
  
• Fungicide modes of action.
  
• Management of fungicide resistance.