Measurements of spectral reflectance from potato plants were carried out in the years 2000 and 2001 using the field radiometer CE 313 of Cimel Electronique Company. Field experiments permitted to perceive differences in the reflectance of electromagnetic radiation from potato plant cultivars Bekas and Mila as well as differences between the plants treated with fungicides providing the protection against Phytophthora infestans and the untreated plants. A differentiation of the values of vegetative indices between potato cultivars resulted from the unequal development rate of the cultivars and from their different susceptibility to Phytophthora infestans. The assessment of potato plants infection by the studied pathogen using spectral measurements agreed with the results of field inspection.
This study describes a newly developed index for predicting and forecasting the first (and potentially subsequent) timing of fungicide application against late blight in potato crops based on weather variables measured close to the crop. Inputs for index calculation were the following: daily minimum temperature, mean relative air humidity and daily precipitation. The decisive moment in the process of forecasting is the sum of daily index values for the previous 5 days. The index was tested in various localities of the Czech and the Slovak Republics for several years with a relatively high success rate exceeding the accuracy of previously applied strategies – NoBlight and negative prognosis. In comparison to the mentioned methods, the calculated index corresponded very well to long-term wet periods and indicated the first application date correctly. In years with no wet periods (in this case, 2015 and 2017), it allowed postponing the first application and reducing the number of required sprays during the growing season. The method does not depend on determining the emergence date, so it can be presented on the internet without cooperation with specific growers in a given locality, and thus supply information for a wider range of users. With knowledge about crop development and the degree of resistance to late blight of grown varieties, users can subsequently choose a specific fungicide and its application date.
In the field experiments performed in 1999–2001 the profitability of late blight control in accordance with three decision support systems: NegFry, Simphyt and Stephan with routine fungicide program was compared. Potato protection carried out according to the recommendations of the decision support systems guaranteed higher profitability of late blight control than when potato was protected routinely. The highest profitability was recorded for susceptible variety Bekas protected according to NegFr.