Methodology to determine fungicide efficacy ratings for the EuroBlight tables – potato late or early blight

Late blight (Phytophthora infestans ) and early blight (Alternaria solani) are the most important diseases in potato cultivation. The control of these diseases depends largely on fungicide sprays during the growing season. Fungicides differ in their efficacy to control any pathogen. The use of effective fungicides is necessary for both the control of the disease and to avoid unnecessary sprays. Each active ingredient has its own efficacies and specific characteristics, which are expressed in fungicide products. A EuroBlight fungicide table was set up to provide an overview of the relative ratings for each characteristic for different fungicides used to control late blight or early blight. Until 2007 EuroBlight fungicide ratings were based on the judgement of experts from the crop protection companies and independent researchers. To objectively evaluate the effectiveness of fungicides, harmonised protocols were discussed, and it was proposed that the ratings of fungicides for the EuroBlight fungicide table were to be calculated, based on results from field experiments carried out over 2 years and in at least 3 European countries. Fungicide ratings derived from the experiments, which indicate the efficacy of fungicides to control potato late blight (foliar and tuber blight) or early blight, were published on the EuroBlight website from 2008. This paper describes the experimental procedure as well as statistical analyses used to derive the EuroBlight fungicide ratings. The procedure allows ratings to be calculated even although candidate fungicides are tested in different years. Overall, the method developed and validated in this study is robust and provides an objective procedure for deriving numeric ratings for fungicides, not just for potato late blight and early blight, but also for other host-pathosystems.