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 so[ani and its effects on yield were evaluated in potato crops in the autumn (fou r experiments), winter (one experiment), and spring (five experiments) growing seasons in Israel. Analysis of disease progress curves reveal ed that early blight is more important in the autumn and winter than i n the spring in the northern Negev region of Israel. Similarly, differ ences in yield between fungicide-treated and nontreated plots were sig nificant (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 tub ers produced per unit area but reduced tuber weight. The efficacy of t he systemic fungicides tebuconazole and difenoconazole against A. sola ni was compared with that of the common protectant fungicides chloroth alonil and mancozeb Tebuconazole significantly decreased lesion expans ion rate and chlorothalonil did not. In some of the autumn and winter experiments, but in none of the spring experiments, the systemic fungi cides were significantly more effective than the protectants in suppre ssion of A. solani.