Phytophthora cactorum

Systematic position and nature of the pathogen: Phytophthora cactorum belongs to the kingdom Chromista, class Oomycetes. It is a notorious soilborne pathogen causing a wide variety of plant diseases. Often referred to as a water mold, it is biologically distinct from true fungi, which significantly influences the choice of chemical control agents and management strategies.

Diseases and host plants: This pathogen is a polyphage affecting over 200 species of plants. It is widely known for causing leather rot in strawberries and crown rot in both strawberries and fruit trees, such as apples and pears. The disease significantly impacts both nursery production and commercial orchards by attacking roots, crowns, and ripening fruits.

Biology and life cycle: The pathogen survives in the soil and plant debris as oospores, which are highly resistant structures. Under favorable moisture conditions, these produce sporangia, which release motile zoospores. These zoospores use water films to swim toward the host roots or fruits, where they encyst and penetrate the plant tissue to establish infection.

Conditions for development and harmfulness: The pathogen thrives in moist, cool to temperate conditions with optimal temperatures ranging between 15°C and 25°C. Its harmfulness is catastrophic, as it can lead to total crop failure due to fruit rotting or sudden wilt of the entire plant. In orchards, it causes collar rot that can kill mature trees within a single season.

Protection and control measures: Effective management requires an integrated pest management (IPM) approach. Key strategies include:

• Selection of certified disease-free propagation material.
• Improvement of soil drainage to prevent waterlogging, which facilitates spore movement.
• Application of specific fungicides, such as metalaxyl or fosetyl-aluminum, when risk is high.
• Sanitation, including the removal and destruction of infected plant tissue.
• Use of straw or plastic mulch to create a barrier between the soil and the fruit in strawberry crops.