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ARS Home » Pacific West Area » Corvallis, Oregon » Horticultural Crops Research » Research » Publications at this Location » Publication #349284

Research Project: Development of Knowledge-based Approaches for Disease Management in Small Fruit and Nursery Crops

Location: Horticultural Crops Research

Title: Heroes and villains: Research identifies harmful and beneficial microbes in nursery soil

Author
item Weiland, Jerry
item Scagel, Carolyn
item Grunwald, Niklaus - Nik
item Foster, Zachary - Oregon State University
item Fieland, Val - Oregon State University
item Santamaria, Luisa - Oregon State University

Submitted to: Digger
Publication Type: Trade Journal
Publication Acceptance Date: 1/12/2018
Publication Date: 3/1/2018
Citation: Weiland, G.E., Scagel, C.F., Grunwald, N.J., Foster, Z., Fieland, V., Santamaria, L. 2018. Heroes and villains: Research identifies harmful and beneficial microbes in nursery soil. Digger. March:25-29.

Interpretive Summary: Phytophthora and Pythium species are common pathogens in nursery systems that can cause rhododendron root rot. Plants with root rot are often stunted, and may wilt and die, thus directly reducing nursery profit. Rhododendrons are an important crop in Pacific Northwest nurseries, but are highly susceptible to these pathogens. We looked at the diversity of beneficial and pathogenic microbes occurring on rhododendron roots from several nurseries and then evaluated the most common pathogen species for their ability to cause disease. Then, we evaluated whether two fungicides were effective for controlling root rot as caused by the two most destructive pathogen species. We found that there are many microbes responsible for decomposing dead organic matter as well as several beneficial microbes that are present on rhododendron roots. We also commonly found three soilborne pathogens. These results are important because they help growers evaluate the risks associated with the presence of each pathogen and show which fungicide control measures are more effective for controlling root rot.

Technical Abstract: Phytophthora and Pythium species are common pathogens in nursery systems that can cause rhododendron root rot. Plants with root rot are often stunted, and may wilt and die, thus directly reducing nursery profit. Rhododendrons are an important crop in Pacific Northwest nurseries, but are highly susceptible to these pathogens. We looked at the diversity of beneficial and pathogenic microbes occurring on rhododendron roots from several nurseries and then evaluated the most common pathogen species for their ability to cause disease. Then, we evaluated whether two fungicides were effective for controlling root rot as caused by the two most destructive pathogen species. We found that there are many microbes responsible for decomposing dead organic matter as well as several beneficial microbes, such as mycorrhizal or potential biocontrol species, that are present on rhododendron roots. We also commonly found three soilborne pathogens: Phytophthora cinnamomi, Phytophthora plurivora, and Pythium cryptoirregulare. Both Phytophthora species caused severe root rot, but P. cryptoirregulare rarely caused significant disease. Soil drenches of two systemic fungicides, mefenoxam and phosphorous acid, were more effective at controlling root rot caused by P. cinnamomi than foliar sprays. These results are important because they help growers evaluate the risks associated with the presence of each pathogen and show which fungicide control measures are more effective for controlling root rot.