The climatic conditions in Northern and Western (NW) Europe, which are very suitable for the cultivation of potatoes, are also very favourable for a range of diseases of which late blight, caused by Phytophthora infestans, is by far the most important with the potential to cause total crop loss. It is controlled by foliar fungicides, with up to 15–20 sprays being used per season. A wide range of fungicides is approved for the control of late blight including nonsystemics (e.g. mancozeb, fluazinam), numerous translaminar compounds (e.g. cymoxanil, dimethomorph, mandipropamid) but few fully systemic fungicides (viz. the phenylamides including metalaxyl-M, and propamocarb hydrochloride). Resistance to metalaxyl appeared in 1980, within a few years of its introduction, and led to control failures in Ireland and the Netherlands. Subsequently, anti-resistance management strategies were developed which allowed continuing use of phenylamides only in mixtures with nonsystemic multisite-inhibiting fungicides and with a limited number of applications. Resistance to other fungicides used to control late blight or early blight (caused by Alternaria spp.) has not developed or has not led to major reductions in control, perhaps in part as a consequence of effective resistance management. The potato is also susceptible to many tuber pathogens, which can cause rots and blemishes and are frequently transmitted via the seed tuber. Relatively few fungicides are approved for tuber or soil application to control tuber diseases. Resistance to thiabendazole, first used on potatoes in the 1970s, developed in several pathogens and resulted in loss of control where it was used alone. Resistance management has focused on avoiding repeated use of thiabendazole during multiple generations of the potato crop and use in mixtures with imazalil. In Europe, resistance has not developed to other fungicides used to control tuber diseases, although pathogen strains resistant to fludioxonil have been reported elsewhere.
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