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Protect Your Citrus Orchard from Phytophthora

October 25, 2019
this agronomic image shows a dead citrus tree caused by phytophthora

California winters typically bring rainstorms across the state. As winter approaches, citrus growers are preparing to defend orchards from Phytophthora, a common pathogen found in CA soils, that thrives in cool, wet conditions. The stress caused by this pathogen is commonly mistaken for water stress and nutrient deficiency.

Because strong, healthy root systems are essential to overall citrus tree health and productivity, it’s important that growers establish an aggressive ongoing management plan for Phytophthora.

this agronomic image shows a citrus tree bark damage caused by phytophthora

Bark damage caused by Phytophthora.

There are 2 main types of Phytophthora that affect citrus:

  • Phytophthora gummosis: Damage symptoms include sap oozing from small cracks in the infected bark creating a bleeding appearance. Eventually, the bark dries, cracks and falls off. Lesions eventually spread around the trunk, and leaves yellow and drop.
  • Phytophthora root rot: Damage symptoms include leaves that yellow and drop, root bark that slides off easily when pinched, water stress, nutrient deficiencies and destroyed feeder roots.

An integrated management system that includes cultural practices and a soil-applied fungicide during root flush in the fall is key to combating Phytophthora. Optimize your citrus tree health with the following:

  • Do not allow water to stand around the crowns of trees or to hit the tree trunk regularly. Provide drainage in low spots of the orchard, areas that are prone to flooding and where water penetration is poor throughout the season.
  • Protect the bark of the tree. Whenever a tree’s bark is harmed or cut, it leaves an opening for the Phytophthora pathogen to enter.
  • Evaluate soil samples. If you are unsure about any of these symptoms, consider taking a soil sample for parasitica or P. citrophthora. Syngenta offers the Soil Pathogen Assessment (SPA), a free program that assesses Phytophthora infections. Contact your Syngenta representative to learn more about soil sampling through the SPA program.

Rotating modes of action is essential to managing for resistance. Ridomil Gold® SL and Orondis® fungicides are high-efficacy rotation partners.

A Group 4 fungicide, Ridomil Gold SL can protect against root rot and increase feeder root growth to ensure better water and nutrient uptake efficiency through the entire tree. The active ingredient, mefenoxam, moves systemically upward in the citrus root system, providing uniform distribution.

Orondis, a Group U15 fungicide, offers an active ingredient, oxathiapiprolin, with a unique mode of action and no cross-resistance to other products. Orondis promotes improved root health and outstanding control of Phytophthora root rot by reducing the number of viable Phytophthora propagules in the soil.

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

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