Initial incidence and development of red core of strawberry

Abstract

SUMMARYThe initial incidence of the disease caused by Phytophthora fragariae in healthy stock of strawberry, cv. Merton Princess, was not affected by different systems of cultivation or by no cultivation for several months before preparing infested soil for planting.In disease development studies, healthy plants which were planted in infested soil in April and sampled at 35‐day intervals showed symptoms of red core on 1 September. Disease severity (mean % number of diseased roots) increased with time and, when averaged over intervals of 70 days, the greatest increases occurred between the end of July and the beginning of October and between December and February. Whereas the former was due to infection of plants in which the total numbers of new roots were low, the latter was due to an increase in the numbers of diseased roots. Most primary roots were produced in October and early November and 75% of the final total were formed by 15 December.Healthy plants of the cvs Cambridge Favourite and Redgauntlet, dug from the field at monthly intervals and challenged with zoospores, were less susceptible in May and June than in other months.It is suggested that a fungicide applied in late September or October would protect the maximum number of new roots and achieve the optimum effect for a single application.