The development of silver scurf (Helminthosporium solani) disease of potato

SUMMARY The main source of inoculum of Helminthosporium solani was the seed tuber; the fungus was not detected in soils in which infected potatoes had been grown the previous year. Lesions spread rapidly on seed tubers after planting, so that within a few weeks the entire surface was covered. As lesions aged they lost the capacity to sporulate, so most inoculum was produced in the first few weeks after planting. Infection of progeny tubers was first detected at the heel (stolon attachment) end soon after their initiation. Once established, lesions spread slowly on the surface of progeny tubers when in the soil; more rapid spread took place during storage. Potatoes which seemed unaffected at lifting became diseased during storage.