Strawberry red stele root rot
Phytophthora fragariae var. fragariae
The egg fungus survives in the soil by means of spores (oospores). Under favorable conditions (host present, soil wetness, soil temperatures between 5 and 20 °C, optimum 10 - 15 °C), these spores germinate and form a spore container (sporangium) in which motile spores (zoospores) are formed. The zoospores are attracted by the exudates of the root and can actively move towards the strawberry root.
Infections occur near the root tips, spreading in the root along the central cylinder toward the rhizome. Under favorable conditions, there is ongoing formation of new spore containers and secondary infections.
Typical for an infestation by red root rot of strawberries are the appearing root symptoms, which take place in spring or shortly after the infection. The main roots become smooth, bare and thickened ("rat tails"). Fibrous roots are largely absent and the central cylinder in the longitudinal root section is red in color.
A nonspecific symptom of damage is the appearance of plants with stunted growth (reduced leaves, shortened stems), usually along plant rows. Fruit development is absent altogether or scab fruit develops and dries up before harvest.
The disease is difficult to determine because typical symptoms are often mild. In case of suspicion, laboratory testing is necessary.
Red root rot of strawberries is particularly dangerous on heavy, stagnant soils and in mild, rainy winters, when a large number of secondary infections occur and the disease spreads rapidly in the field. Another problem is loss of area due to the very long-lived oospores. These permanent organs can survive in the soil for ten to 15 years without host plants, and replanting strawberries on these areas is practically impossible.
In Western Europe (UK, Netherlands, etc.), the disease is therefore much feared. In the main growing areas of eastern Austria, red root rot is only of local importance due to the rather sandy, light soils and the cold winters.
Prevention and control
- Purchase of controlled certified planting material and immediate inspection of the plants upon delivery to the company.
- Examination of the planting material for latent infections
- Planting on soils where no strawberries have been cultivated so far
- Field plots where infestation by red root rot has been detected in the past should no longer be used for strawberry production
- Dam cultivation in heavy soils
- use of plant protection products can reduce the spread of the pathogen (see list of plant protection products approved in Austria)
- regular infestation control during cultivation
- Measures in case of suspected red root rot of strawberries: Remove and destroy diseased plants without causing damage to prevent further spreading
Last updated: 17.12.2021