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Fungicides, Fungal Resistance to Chemical Controls

  1. Derek Hollomon

Published Online: 15 APR 2003

DOI: 10.1002/047126363X.agr099

Encyclopedia of Agrochemicals

Encyclopedia of Agrochemicals

How to Cite

Hollomon, D. 2003. Fungicides, Fungal Resistance to Chemical Controls. Encyclopedia of Agrochemicals. .

Author Information

  1. University of Bristol, Bristol, United Kingdom

Publication History

  1. Published Online: 15 APR 2003


The long-term viability of pesticides to control pests, diseases, and weeds is always threatened by resistance. Consequently, there is a need to understand the causes of resistance and the factors that influence its spread, so that the problem can be managed effectively. Chemical pesticides bind to specific sites in their target proteins, and small changes can disrupt this binding. High levels of resistance are often conferred by just a single amino acid change, and the same change causes resistance to a pesticide group in different species, and even phyla. Surprisingly, these changes are generally in highly conserved regions of the target protein. Other mechanisms, such as detoxification, increased efflux associated with multidrug resistance (MDR), overexpression of the target protein and altered metabolic pathways all contribute to resistance, but generally these mechanisms confer lower levels of resistance than target site changes.

Biochemistry provides ways to generate resistance, but individuals possessing these mechanisms must not suffer fitness penalties as a consequence. Bioassay remains the main way to monitor resistance, although it is often resource intensive, and it provides little information on the mechanism conferring resistance. Biochemical and DNA methods offer ways to overcome these difficulties, and they are increasingly used to monitor resistance where mechanisms are known.

Combining all this information allows assessment of resistance risk and implementation of strategies to manage the problem. Predictive modeling can be useful, but there is always an empirical component in developing anti-resistance strategies. A corner stone of all anti-resistance strategies involves using pesticides with different modes of action, and integrating this with nonchemical control measures. Examples of successful anti-resistance strategies are few, and effective control often rests with the development of new pesticides with novel modes of action.


  • target-site;
  • single nucleotide polymorphism (SNP);
  • multidrug resistance (MDR);
  • gene amplification;
  • fitness;
  • monitoring;
  • anti-resistance strategies