INFLUENCE OF MINERAL NUTRITION ON DEVELOPMENT AND HARMFULNESS OF POTATO ALTERNARIOSIS IN THE NORTH-WEST OF RUSSIA
The conducted research showed that the number of cases of the potato plantations heavy damage with the early blight on the Northwest of Russia is growing. The intense development of this illness occurred in the years with the high average diurnal temperatures in the second and third decades of June along with the high level of precipitation in the first decade of July. The application of the full mineral fertilizer leaded to the later emergence of the illness symptoms (7-10 days more) and significant decrease in the plant lesion intensity of the potato with early blight (by 1,4-2,0 times). In years favourable for the development of alternariosis, a strong defeat of potatoes with this disease occurred on all variants of fertilization. The assessment of the harmfulness of the disease showed that variants with an increased level of mineral nutrition had a more pronounced negative effect of alternariosis on the formation of potato productivity. The coefficients of the harmfulness of this illness characterizing the decrease of the productivity of the potato plants in respect to the each point of the leaf surface lesion were 14,15, 65,61 and 80,97 g per plant (2,4, 5,3 and 5,8%) for the low, medium and strongly fertilised plants, respectively. However, the reliable productivity decrease of the plants with the 5-25% of leaf surface covered with the early blight lesions has not been recorded. If the plants are strongly affected with the early blight, the harvest loss can reach 25%, and the number of marketable tubers can decrease by 21-33%. Therefore, in years of severe development of alternariosis there is an increasing expediency in fungicide treatment to protect potato from early blight on fertilized plantations.