In the recent years earlier appearance of late blight on potato crops and the increase of infection pressure of Phytophthora infestans has been observed due to the changes in its population. The occurrence of P. infestans on potato plants at early plant growth stages points to the possibility of existence of other infection sources such as infected seed tubers or volunteer plants and their increasing role in the disease epidemiology. These changes have led to late blight epidemics developing earlier and more severely than previously and changes in the occurrence and development of first symptoms of P. infestans infection on potato plants. In the years 1997–2006, field studies were conducted at the Plant Breeding and Acclimatization Institute of Bonin with the emphasis on comparison of time of the occurrence and incidence level of late blight of potato. The criteria for pathogen infection pressure assessment were assumed to be the percentage of haulm destruction at the end of growing season and area under the disease progress curve (AUDPC), the late blight development rate defining the increase of destruction of above ground plant parts in unit time and also tuber yield and its healthiness. The observations carried out at Bonin revealed that both time of occurrence and severity of late blight differed and were dependent upon meteorological conditions and upon the year. Late blight occurred the earliest at Bonin in 2001 (42 days after planting). The time of occurrence of late blight depends upon rainfall in May and June. A very high infection rate of the pathogen was observed, particularly in 2006 (0.517) and in 2004 (0.400) despite late time of late blight appearance in the season. In these years AUDPC on the unprotected cultivar was 0.071 and 0.508, respectively. The 10 years of observations conducted at Bonin revealed that the yield and occurrence of tuber late blight depended mostly upon meteorological conditions in particular years.

The field experiment carried out in Winna Góra compared the efficacy of fungicide programs applied in accordance with the NegFry and Routine systems. The results of2002 validation achieved in Winna Góra showed that NegFry model forecasting the late blight occurrence is useful in Polish climatic conditions. Compared with routine treatment schemes, NegFry recommended fewer treatments without significant reduction of yield thus potato protection according to NegFry was more cost-effective than according to Routine system. Basing on these facts the NegFry decision support system can be recommended for Polish climatic conditions.

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.

The NegFry model used for timing the chemical control of potato late blight was validated in field trials at Bonin in the years 2001-2002 (4 trials). In these trials the number of fungicide treatments recommended by NegFry was about 34.5% lower (on average) than the number of treatments in a routine spraying scheme. This reduction was mostly the results of a delay in the time of the initial fungicide application and longer spraying intervals recommended by Negfry.

The Internet based 'Web-Blight' service (http://www.web-blight.net) was initiated to provide an online warning and prognosis system for potato late blight in the countries around the Baltic Sea. In order to obtain comparable results, methods were harmonized and a set of interacting PC and Internet applications were developed for use by the project partners. Results regarding monitoring of potato late blight and evaluation of variety resistance against late blight (field tests) are presented for Estonia, Latvia, Lithuania and Poland. The use of the Internet to collect and present data was very successful, because information were "on the fly", helping farmers in their decisions about the timing of first applications and choice of fungicide type. Results show that it was possible to find early attacks as primary attacks (spots in the fields). In most cases attacks were initially found in home gardens and later in conventional fields. The growth stage at first attacks was often higher than 3 7 (BBCH) indicating that very early attacks caused by oospores in the soil was not a widespread problem. Local varieties were tested for late blight resistance in untreated field trials against four test varieties (Sava, Oleva, Danva and Kuras), Primary disease data were uploaded to Web-Blight via the Internet, and applications on the Web-Blight server calculated epidemiological variables such as delay of first symptoms and RAUDPC. Results indicated the presence of race-specific resistance in some varieties, e.g. Kuras, and that some varieties were originally misclassified according to resistance scale, e.g. Sante. The network about observation trials clearly showed that field test of variety resistance against late blight in time and space is important, taking into account the rapid evolution of Phytophthora infestans populations in Europe.

As compared to 1977 potato acreage in Poland has decreased by about 1.4 million hectares and amounted to 958 thousand hectares in 2002. Potatoes are protected mainly against Leptinotarsa decemlineata Say, Phytophthora infestans and weeds. Number of chemical treatments against Colorado potato beetle fluctuated between 1.1. to 1. 7 per year, in average. In 1977-1987 mainly organophosphorous insecticides were applied, whereas in last years pyrethroids and nereistoxin were used. Chemical treatments against late blight fluctuated between 1.2 to 1.6 per year, in average. Observations performed in 1977-2002 showed that the application of contact fungicides considerably decreased. In weed control in potatoes only one treatment, in average, was performed using herbicides, mainly pre-emergence ones. Herbicides containing linuron and metribuzin were most frequently applied.

In this study defense responses in three potato varieties with different levels of reaction to the late blight disease caused by Phytophthora infestans were analyzed after inoculation with the pathogen. In the resistant cv. Pastusa Suprema, increased intensity of H2O2 and callose deposit accumulation was observed beginning at 24 hours after inoculation, followed by a hypersensitive response at the inoculation points. In the moderately resistant cv. Diacol-Monserrate, the same responses were observed as in the resistant variety, but with less intensity over time. For the susceptible cv. Diacol-Capiro, the responses observed occurred later than in the other two varieties, subsequent to the advance of the pathogen over extensive necrotic areas. These results suggest that early, intense peroxide and callose accumulation and a hypersensitive response are associated with the observed resistance of the cv. Pastusa Suprema and cv. Diacol-Monserrate to P. infestans.

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.