Red stele root rot

Red stele root rot, caused by the oomycete Phytophthora fragariae, is a severe soil-borne disease affecting strawberries. The pathogen attacks the root system, specifically targeting the vascular cylinder, which leads to the decay of fine root hairs. As a result, the plant loses its ability to absorb essential nutrients and water, eventually leading to the total collapse of the strawberry plant.

The primary host for this pathogen is the cultivated strawberry. While it may seem like a localized issue, the disease is notoriously persistent and can thrive in infested soil for years without a host. This makes it a significant threat to commercial berry production, often rendering land unsuitable for strawberry cultivation for extended periods if left unmanaged.

Symptoms often appear in spring or during periods of active growth. Infected plants show stunted growth, leaf discoloration (reddening or bluish tints), and sudden wilting under water stress. The most definitive diagnostic feature is the red-brown discoloration of the root core, known as the "red stele," which can be observed when cutting a primary root longitudinally.

The disease thrives in cold, wet conditions. The pathogen's zoospores are motile in water, meaning that heavy rainfall, poor soil drainage, and over-irrigation are the primary drivers of its spread. Because the spores move through the soil water film, once a field is contaminated, the spread can be rapid across the entire planting area if environmental conditions remain favorable.

• Always use certified disease-free nursery stock for new plantings.
• Improve soil drainage by using raised beds or installing tile drains.
• Rotate crops and avoid replanting strawberries on the same site for 5–7 years.
• Apply systemic fungicides specifically registered for Phytophthora control.
• Immediately rogue out and destroy symptomatic plants to prevent spore buildup.

Management of red stele focuses almost entirely on prevention and cultural practices. Once an area is infested, eradication is extremely difficult. Agronomic strategies should prioritize site selection, water management, and rigorous biosecurity measures when introducing new plants. By minimizing the conditions that favor water saturation, growers can significantly reduce the risk of this devastating pathogen destroying their strawberry crops.