Phytophthora citricola root rot

Phytophthora citricola is a devastating soil-borne oomycete pathogen responsible for various forms of root and crown rot. Because it thrives in waterlogged environments, it is often classified alongside other Phytophthora species as a primary cause of decline in high-value agricultural and ornamental crops.

The host range of this pathogen is extensive, affecting economically important crops such as citrus, avocado, walnut, and various nursery-grown woody ornamentals. In some regions, it also causes significant damage to small fruits like strawberries and certain vegetable crops, leading to substantial agricultural losses.

Symptoms typically manifest as poor canopy development, chlorosis, and wilting. A diagnostic sign is the presence of dark, sunken lesions on the lower trunk or crown area. Beneath the soil, the root system shows signs of decay, necrosis, and a distinct lack of fine, feeder roots, which prevents nutrient and water uptake.

Development is driven by excessive moisture and poor soil aeration. Zoospores require water to swim and infect host tissue, making rainy seasons or over-irrigation high-risk periods. The pathogen persists in the soil through thick-walled oospores, which allow it to survive periods of dryness and cold, re-infecting new plantings.

Effective management requires an integrated approach. Cultural practices such as improving soil drainage, utilizing raised beds, and managing irrigation schedules are vital. Chemical control involves the application of phosphonate-based fungicides or other oomycete-specific chemicals to manage disease pressure and protect the root health of the crops.

• Improve soil drainage and aeration.
• Use certified, disease-free nursery stock.
• Avoid excessive irrigation and waterlogging.
• Apply targeted fungicide treatments.