Overwintering en epidemiologie van Phytophthora infestans, tevens enige nieuwe bestrijdingsmogelijkheden

Primary foci of phytophthora. could be found in potato fields originating from diseased tubers and on refuse heaps. In De Streek (North Holland) the very susceptible variety Eersteling had I primary focus per 80 ha of potatoes. Infection from refuse heaps was there of minor importance. Only a small proportion of diseased tubers planted gave a primary focus. Spread from the primary foci was studied. Epidemics of phytophthora. under the prevailing weather conditions could be easily explained by spread from the primary foci. 'Field resistance' of the varieties plays a main role in epidemics. A method for testing it in the greenhouse was worked out.The disease could be controlled not only by spraying but also by careful inspection of seed potatoes and by eradication of primary foci in field and on refuse heaps. Heat treatment of tubers killed the fungus, but would hardly be applicable in practice.<p/