Fungicide Resistance Guidelines from AHDB and FRAG-UK

Resistance occurs when a pathogen becomes so insensitive to a fungicide that the fungicide’s field performance is impaired. Resistance can arise rapidly and completely so that disease control is lost in a single step. More commonly, resistance develops gradually so that the pathogen becomes progressively less sensitive. When this happens there is usually no initial detectable loss of control, but it may decline over time.
News article

Potato late blight, caused by Phytophthora infestans, has been the major disease of potatoes since its introduction to the UK in 1845 causing losses by destroying foliage and by infecting tubers.  Fungicides continue to be an important component of late blight control with up to 15-20 applications being used per season.

Copper compounds were first used to control late blight in the 1890s.  By the 1960s, these had been largely superseded (except in organic production) by other broad spectrum contact fungicides such as dithiocarbamates.  The introduction in the late 1970s of the phenylamides brought a new dimension to blight control, but was quickly followed by the development of phenylamide-resistant strains of the pathogen.  In countries where phenylamides were applied as the sole active ingredient for late blight control, notably The Netherlands and the Republic of Ireland, this led in 1980 to a complete failure of disease control with concomitant crop losses.  This experience highlights the need for measures to minimise the risk of resistance development.

For further information download the FRAG-UK guidelines from the AHDB website.


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