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.

The influence of different nozzle types and adjuvants on the biological efficacy of fungicides in potato was investigated in four growing seasons in the years 1997-2000. The studied foliar plant disease was late blight (Phytophthora infestans). The biological efficacy of fungicides (alone or with adjuvants) applied with coarse air induction nozzles was comparable to fine standard flat fan nozzle. The differences between the nozzle types tested were small in control oflate blight in potato with systemic and contact fungicides. Coverage of upper side of leaf blades was from three to four times higher than lower side of leaf blades. In general, the highest coverage of upper and lower side of leaf was achieved when the full dosage rate of fungicide (copper oxychloride) was used with both the flat fan XR 110-03 and air induction DB 120-03 nozzle. Adding Atpolan 80 EC and Zero Piany 62 SL to 50% dosage rate of copper oxychloride decreased the spray coverage on lower side ofleaf as well as with both the XR 110-03 and DB 120-03 nozzles. However, addition of adjuvants to spray solution did not decrease the deposition on upper side of leaf blade. In general, adjuvants did not considerably influence the biological efficacy of the fungicide treatments sprayed with both the flat fan and the air induction nozzles but had favourable influence on potato yield.