The development of Alternaria solani Sor. on potatoes cultivated in monoculture

The purpose of the research was to determine the intensity of the development of early blight of potatoes (Alternaria solani Sor.) in different weather conditions and its influence on the yield formation of potatoes cultivated in monoculture over the years 2005-2007. The development of A. solani with 10 days interval was assessed in field trials on the variety 'Saturna' cultivated for industrial purposes. The intensity of potato early blight was affected by the weather conditions. The highest severity was observed under elevated air temperature and sufficient moisture in July, the lowest - under conditions of a long dry period. The increase of severity on leafs from 13.1% at the beginning of August in the first year of cultivation to 22.6% in the third year was observed that confirmed also a dependence of disease intensity on accumulation of infection in soil by monoculture. The disease causes a relatively moderate reduction of yield. The loss of yield associated with intensity of early blight on potato leaves during the active formation of tubers was described by the relationships: y = - 0.5398x + 26.187 (R-2 = 0.25) or y = - 0.4268x + 17.197 (R-2 = 0.22), the regressions were statistically significant (P < 0.05). The application of fungicides significantly limited the development of early blight on leaves and tubers of potatoes, but over all years of research just a moderate control of the disease was observed. The increase of damage of early blight over the last year was connected with insufficient activity of fungicides applied for the disease control on potatoes (mainly against Phylophthora infestans), thus indicating the possibility of another outbreak of the disease in the coming years.