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Protect Permanent Crops from Phytophthora Root Rot

September 19, 2022

Despite several years of drought affecting CA, there is an underground issue: Phytophthora root rot in your citrus and tree nuts. This fungal disease infects the tissue of a tree’s feeder roots and can severely limit the uptake of water and nutrients.

Phytophthora root rot causes a gradual waning of tree health and productivity, which often goes unnoticed, delaying treatments that can reverse damage from the disease. Phytophthora also shares symptoms ― thinning canopies, twig dieback and soft, discolored outer root tissue ― with other destructive forces, including drought, high salinity, nematodes and root weevils, making diagnosis even more difficult.

Listen as Chris Clemens, Syngenta agronomy service manager for the Western region of the U.S., discusses what you should know about this disease.

Clemens recommends these strategies to help stop Phytophthora root rot before it causes damage:

  • Begin the season with clean, high-quality stock. Lower quality trees are more likely to have infected soil or roots that can quickly spread.
  • Avoid over-irrigation. Trees that become oversaturated for over 24 hours are much more susceptible to the growth and spread of this disease.
  • Sample soils regularly. To confirm whether symptoms are being caused by Phytophthora root rot or another force, test soils and trees during spring, summer and fall. Syngenta offers a Soil Pathogen Assessment (SPA) program to gauge Phytophthora propagules in CA and AZ permanent crops.

Another effective component of a management plan is an application of a fungicide like Ridomil Gold® SL fungicide in the spring and Orondis® fungicide in the fall for preventive and residual control. Even at low-use rates, Orondis protects roots by reducing propagule count and inoculum potential. By encouraging strong root development, Orondis consistently increases root mass, which leads to better nutrient and water uptake, and a reduction in tree stress and pest pressure. Phytophthora root rot is a chronic problem, so changes or improvements in tree condition will be seen over time.

Listen to the full interview with Clemens, originally posted by the Thrive® podcast.

To learn more about soil sampling through the SPA program, contact your Syngenta representative.

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All photos are either the property of Syngenta or are used with permission.