The effect of irrigation and nitrogen on powdery scab and yield of potatoes

Powdery scab, caused by the fungus Spongospora subterranea, has developed in the Cappodocia region of Turkey because of changes in agronomic practices, such as excessive irrigation and nitrogen fertilizer use and growth of highly susceptible cultivars. The most Suitable irrigation and nitrogen application levels were established to maintain powdery scab at minimum levels without affecting potato yield. Three irrigation levels were used in 1998 (673, 897, 1121 mm) and five in 1999 (329, 494, 658, 823, 987 mm). Nitrogen levels were applied 150, 300, 450, 600 kg N ha(-1). In 1998, least powdery scab occurred with 673 mm irrigation, which yielded 41 t ha(-1) potatoes. The lowest disease severity occurred in 1999 with 494 mm irrigation and 150 kg N ha(-1). At these levels, tuber yield was 34 t ha(-1) which was not significantly different from the highest yield measured. In 1999 and at two of the three irrigation levels in 1998, nitrogen increased disease severity.