There has been a gradual increase in the occurrence of fungicide resistance since the early 1970s. Resistance is usually first recognised when expected levels of disease control in the field are no longer achieved using commercial doses of the fungicide. Fungicide resistance can sometimes arise rapidly and disease control can be lost partially or completely. Sometimes it can be a gradual process resulting in a loss of control over many years. Examples of these types are common throughout Europe.
Many types of resistance mechanism are known. By far the commonest mechanism appears to be an alteration to the biochemical target site of the fungicide. This could explain why many of the older products, which have no specific target site, have not encountered resistance problems. In contrast, modern fungicides act primarily at single target sites, and are often referred to as single-site fungicides. In this case, a single gene mutation can cause the target site to alter, so as to become much less affected by the fungicide. Different amino acid changes can cause different levels of resistance.
Factors influencing resistance
The risk of development of resistance is linked to a number of factors including the specific mode of action (MOA) of the fungicide, the biology of the target pathogen and the level of exposure of the pathogen to the fungicide. Resistance management is vital to maintain effective control whilst minimising over-exposure of the pathogen and reducing the risk of resistance developing.
Source of information: FRAC, Arvalis, FRAG UK, Norbarag. Updated May 2015, by Lise Nistrup Jørgensen