Red stele root rot

Phytophthora fragariae belongs to the kingdom Chromista, genus Phytophthora, species fragariae. It is an oomycete that causes a destructive disease known as red stele (or red core root rot) in strawberries. This pathogen is highly specialized and is recognized as a significant threat to strawberry production worldwide, often necessitating strict quarantine measures.

The disease primarily affects the root system of strawberry plants. The characteristic symptom is the decay of the root's vascular cylinder, which turns a distinct reddish-brown or brick-red color, while the outer cortex may initially remain white. Affected plants typically show stunted growth, wilting, and purple or reddish discoloration of the older leaves, eventually leading to the death of the entire plant.

The life cycle of the pathogen is driven by moisture. Phytophthora fragariae produces motile zoospores that swim through water-saturated soil to infect young strawberry roots. Under dry conditions or lack of a host, the fungus forms thick-walled oospores, which are survival structures capable of remaining viable in the soil for many years, making eradication difficult.

The spread of the disease is favored by cool, wet weather and poorly drained or heavy soils where water stagnates. Once the pathogen is introduced into a field via infected transplants or contaminated soil on machinery, it spreads rapidly through surface water runoff. Because infected plants cannot be cured, prevention is the only effective management strategy.

Key control and management practices include:

• Planting only certified, disease-free nursery stock.
• Utilizing well-drained, raised beds to minimize soil saturation.
• Strict adherence to long-term crop rotation schemes.
• Sanitizing field equipment, boots, and tools to prevent cross-contamination.
• Applying fungicides, such as metalaxyl or fosetyl-aluminum, as a preventative treatment in infested areas.