Effects of growing season and fungicide type on the development of Alternaria solani and on potato yield

The intensity of early blight disease caused by Alternaria solani and its effects on yield were evaluated in potato crops in the autumn (four experiments), winter (one experiment), and spring (five experiments) growing seasons in Israel. Analysis of disease progress curves revealed that early blight is more important in the autumn and winter than in the spring in the northern Negev region of Israel. Similarly, differences in yield between fungicide-treated and nontreated plots were significant (P < 0.05) in four of the five autumn and winter experiments (20.6 to 24.0% increase) but in none of the spring experiments. In the autumn and winter seasons, early blight did not affect numbers of tubers produced per unit area but reduced tuber weight. The efficacy of the systemic fungicides tebuconazole and difenoconazole against A. solani was compared with that of the common protectant fungicides chlorothalonil and mancozeb. Tebuconazole significantly decreased lesion expansion rate and chlorothalonil did not. In some of the autumn and winter experiments, but in none of the spring experiments, the systemic fungicides were significantly more effective than the protectants in suppression of A. solani.