VIEW ARTICLE

Ecology and Epidemiology

Influence of Flooding Duration on Development of Phytophthora Root and Crown Rot of Juglans hindsii and Paradox Walnut Rootstocks. M. E. Matheron, Former graduate student, Agricultural Research Service, U.S. Department of Agriculture, Department of Plant Pathology, University of California, Davis 95616, Present address of senior author: Department of Plant Pathology, University of Arizona, Yuma Mesa Agricultural Center, 6425 West Eighth Street, Yuma 85364; S. M. Mircetich, professor, Agricultural Research Service, U.S. Department of Agriculture, Department of Plant Pathology, University of California, Davis 95616. Phytopathology 75:973-976. Accepted for publication 26 March 1985. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1985. DOI: 10.1094/Phyto-75-973.

Two-month-old seedlings of Juglans hindsii were grown for 3 mo in soil artificially infested with Phytophthora cryptogea, P. citrophthora, P. citricola, or P. cinnamomi and subjected to biweekly flooding periods of 0, 6, 12, 24, or 48 hr. The severity of root and crown rot caused by P. cryptogea and P. citrophthora increased as the length of the flooding periods was increased. A similar relationship was observed when Paradox seedlings were grown in soil infested with P. citricola. In contrast, seedlings of J. hindsii planted in soil infested with P. citricola or P. cinnamomi, and Paradox seedlings planted in soil infested with P. cinnamomi, suffered severe root and crown rot in unflooded soil as well as in soil flooded for 48 hr. The results suggest that careful soil-water management should minimize losses of English walnut trees in orchards containing rootstock of J. hindsii and infested with P. citrophthora or P. cryptogea, or in orchards containing Paradox rootstock and infested with P. citricola.