Soilborne Diseases of Nursery Crops

agricultural gypsum

USDA-ARS and OSU Team Up to Tackle Soilborne Diseases in Nurseries

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By Dr. Jerry Weiland, Dr. Carolyn Scagel, Dr. Nik Grunwald, Dr. Val Fieland, Zach Foster, Dr. Luisa Santamaria, and Gilbert Uribe

Soilborne diseases pose a significant threat to the health of nursery plants. To address this pernicious problem, the Horticultural Crops Research Laboratory (USDA-ARS) and Oregon State University have joined forces. Thanks to funding from the Floriculture and Nursery Research Initiative, we are studying the interaction between soilborne diseases and the environment, including factors such as irrigation, nutrient cycling, and soil conditions, to improve disease management and soil health in nursery production.

Identifying Common Soilborne Pathogens

Our research team, composed of experts in nursery production, plant pathogens, mycorrhizae, plant physiology, and extension services, has set out to achieve several objectives:

  1. Identify the most common soilborne plant pathogens in commercial nursery production systems, including Pythium, Phytophthora, and Verticillium species.
  2. Develop assays that growers can use to detect these pathogens.
  3. Evaluate disease control methods.
  4. Characterize the roles of soil fungi in nutrient cycling and soil health.

Initially, our focus was on studying soilborne diseases that affect rhododendron production. Rhododendron is a popular crop in the Pacific Northwest nursery industry, and our findings on this crop can benefit a large number of regional growers.

Common Soilborne Pathogens in Rhododendron Production

Through surveys conducted in cooperating nurseries involved in rhododendron production, we have found that Phytophthora (Ph.) and Pythium (Py.) species are the most common soilborne pathogens affecting all stages of rhododendron production. The three most frequently encountered pathogens causing root rot in diseased plants are Ph. cinnamomi, Ph. plurivora, and Py. cryptoirregulare. These pathogens have wide host ranges and can infect many plant species in the nursery trade, including trees, shrubs, flowers, vegetables, and fruits.

Microbiome Analysis: A Powerful Tool for Pathogen Identification

To gain a broader understanding of the microbial communities associated with nursery crops, we are using microbiome analysis. This method involves extracting DNA from plant and soil samples and sequencing barcoded samples to identify fungi and bacteria present. This approach allows us to identify both pathogenic and beneficial microbes associated with nursery plants, including the elusive ones that cannot be cultured using traditional methods. By identifying the most common pathogens and beneficial fungi present, we can develop effective disease management strategies for the nursery industry.

Evaluating Disease Control Treatments

Rhododendron growers face economic risks due to Ph. cinnamomi and Ph. plurivora infections, but there is limited information on effective disease control treatments. We are conducting studies to determine the efficacy of fungicides and gypsum soil amendments in managing these pathogens. The results will inform the development of guidelines and disease control strategies that can be applied to a wide range of nursery crop species.

Effects of Irrigation on Disease Development

We are also investigating how irrigation practices influence disease development. Water availability plays a crucial role in the infection frequency and severity of Phytophthora and Pythium species. Understanding this relationship will help us develop irrigation practices that optimize water use while minimizing disease development and promoting plant health. By examining the effects of varying irrigation treatments on disease development and plant growth, we aim to provide growers with valuable insights for mitigating root rot.

Our Commitment to Soilborne Disease Management

Soilborne diseases are a common challenge in nursery production. By focusing our research on identifying pathogens and understanding their behavior using advanced techniques like microbiome analysis, we can reduce their impact on nursery crops. Our initial research on rhododendron production will pave the way for future studies on other plant species. With the knowledge gained from this research, we can help nursery growers improve disease management and promote healthier soil in the Pacific Northwest.

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