Controlling late blight with resistant potatoes
Potatoes are an important cash crop for organic farmers throughout the European Union and the disease potato late blight can result in serious economic losses. Therefore, a ban on copper-based fungicides would result in greater losses for farmers unless alternative ways of combating blight can be developed. The BLIGHT-MOP project developed improved commercially viable organic production systems which can manage potato blight without resorting to copper fungicides. The aim of the project was to maintain the same quality and crop yield as obtained with the use of these fungicides. Researchers noted that resistant varieties of potatoes consistently achieved the most effective control of blight on foliage and tubers in contrast to diversification and agronomic strategies. Resistant varieties also gave better results than alternative treatments to copper-based fungicides. Although resistant varieties did not always provide higher yields than susceptible ones, they did reduce the level of disease and the risk of infection within and between crops. Application of copper oxychloride to both susceptible and resistant potatoes resulted in a slight improvement in blight control and crop yield in the most resistant varieties. It appeared, therefore, that cultivation of resistant varieties was the most effective way to reduce or eliminate altogether the need for copper based-fungicides in organic agriculture. The BLIGHT-MOP team concluded that applications of copper-based fungicides could be reduced by around 16.5% to 50% of current levels. This can be achieved by growing the maximum amount of resistant varieties that the market can bear. However, this can only be realised if the resistant varieties are acceptable to the organic market and more popular susceptible varieties replaced without incurring economic losses.