EFFECT OF SOIL-WATER TENSION AND HARVEST TIME ON LEVELS OF INFESTATION BY PHOMA-FOVEATA FOISTER IN SOIL AND ON TUBERS AND STEMS OF POTATO (SOLANUM-TUBEROSUM L) IN NORTHERN SWEDEN

The incidence of P. foveata in soil and tuber samples from field experiments often increased significantly as the harvest season progressed and temperatures fell. Mean levels of tuber and soil infestation were significantly higher in irrigated rows compared with those artificially sheltered from precipitation, both at normal and late harvest dates. Soil infestation was most frequently detected within 10 cm of the parent tuber. No pycnidia were visible on the haulm, and very few latently infected stem segments and leaves were detected using various methods. In three out of four years, the incidence of P. foveata in tubers after wounding was reduced by washing them gently in tap water immediately after harvest.