Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 8/3/2018
Publication Date: 8/15/2018
Citation: Weiland, G.E., Grunwald, N.J., Scagel, C.F. 2018. Disease control of Phytophthora plurivora and other Phytophthora species infecting European beech and rhododendron in the United States. Meeting Abstract for LIFE+ ELMIAS Ash and Elm, and IUFRO WP 7.02.01 Root and Stem Rots Conference (LIFE-IUFRO); 2018. Aug 26-Sept 1; Uppsala and Visby, Sweden.
Technical Abstract: Phytophthora plurivora is a root rot, canker, and foliar pathogen that is thought to have been spread worldwide by the nursery industry. The pathogen may be native to southeast Asia, where it is found in the soil and rhizosphere of apparently healthy trees in the forests of China, Nepal, and Taiwan. However, in Europe, P. plurivora is associated with root rot of forest tree species and causes blight of rhododendron and other ornamentals in nurseries. In the United States (U.S.), P. plurivora is one of several Phytophthora species causing canker on mature, landscape European beech trees and is an important foliar and root rot pathogen in nurseries on ornamental nursery crops, including rhododendron. Recent nursery surveys (2013-2017) have shown that P. plurivora and P. cinnamomi are the most common species causing root rot of rhododendron in the northwest U.S. Yet, despite decades of research, Phytophthora root rot remains a significant problem in the nursery industry. A better understanding of the diversity of Phytophthora species involved and how that diversity affects disease control is needed to improve disease control efficacy and thereby minimize the spread of invasive pathogens in the nursery industry. Here, we report on fungicide treatments that were successfully used to treat cankers on European beech trees and on our recent efforts to improve the efficacy of fungicide treatments for rhododendron in the nursery industry. Differences in sensitivity to mefenoxam and phosphorous acid, the two most commonly used fungicides, were observed among Phytophthora species and isolates infecting both European beech and rhododendron. In addition, the method of fungicide application was critical for achieving disease control for both hosts: bark drenches were most effective for canker control on European beech while soil drenches were most effective for root rot control of rhododendron. Research is underway to determine whether the differences in fungicide sensitivity affect disease control in rhododendron.