Biology and Control of Soilborne Fungal and Oomycete Pathogens Affecting Washington's Specialty Potato Industry

Non-Technical Summary: Red, yellow, white and blue specialty potatoes are the mainstay of western Washington's agricultural base with over 12,500 acres in production annually, at an estimated farmgate value of $ 100+ million. These cultivars, grown primarily for the fresh market, command a higher price and have multiple value-added traits when compared to Russet type potatoes destined for processing, providing that size distribution and tuber quality meet fresh market requirements. Such attributes can be affected by soilborne pathogens which cause disease on potato stems, stolons, roots and tubers. Research to understand, and strategies to protect, Washington's specialty potato crops in the context of certain soilborne pathogen-caused problems is essential. Both the future of western Washington agriculture, and the specialty potato production areas near Ellensburg, Yakima, Pasco and Hermiston (where these cultivars are grown under irrigation in the Columbia Basin) stand to benefit from new information and education. <P> Approach: Common scab: Refine a greenhouse bio-assay technique to enable growers, particularly organic potato growers, to predict soil population levels of S. scabies and make informed cropping decisions relative to planting date, cultivar selection, soil amendments, and irrigation practices. Utilize the bio-assay to evaluate cultivar resistance and efficacy of bio-pesticides as seed tuber treatments for common scab control. Compile and disseminate information obtained from the 3-year organic transition cropping study, completed in 2006. Rhizoctonia: Write scientific article on effects of soil fumigation on incidence and severity of tuberborne Rhizoctonia disease, previously completed. Silver scurf and Fusarium dry rot: Using standard field survey and laboratory techniques, determine whether recent increased severity of these diseases result from thiabendazole-insensitive strains. Employ standard amended culture media-techniques for detection of TBZ and other fungicide-insensitive strains of Fusarium, Helminthosporium, Phytophthora, and Pythium. Utilize (PCR)-based detection methods developed for H. solani to study epidemiology of TBZ-sensitive and TBZ-insensitive strains in potato fields and storages. Screen new seed-piece fungicides including various bio-pesticides, evaluate cultivar sensitivity at different seed tuber and soil inoculum densities, and evaluate impact of harvest date relative to vine-desiccation in order to augment recommendations for both dry rot and silver scurf control programs. Tuber rots: Work with potato geneticists and horticulturists on continuing to evaluate specialty tuber cultivars and breeding lines and new germplasm materials for resistance to tuber rots as well as other soilborne diseases. Utilize previously developed laboratory, greenhouse and field evaluation techniques to the fullest extent possible. Create extension materials on relative resistances of specialty potato cultivars to various tuber rot diseases. Verticillium: Complete experimental field and greenhouse work on use of broccoli green manure amendments for control of Verticillium wilt on potato. Write scientific article summarizing findings of recent three-year study with Dr. du Toit on susceptibility of V. dahlaie on selected vegetables in northwestern Washington. Extension: Expand PNW-VEG Team activities will be expanded to audiences broader than potato growers, to meet the interests and funding opportunities of community organizations interested in high quality, fresh and cultivar-specialized produce. Continue to i) assist with vegetable disease diagnoses, ii) provide growers and gardeners with resources on managing vegetable diseases in environmentally sound ways, iii) publish new information about vegetable pathogens, and iv) help maintain the team's website