Rosellinia root rot

Rosellinia root rot is a severe fungal disease caused by pathogens of the genus Rosellinia, most notably Rosellinia necatrix. This fungus primarily attacks the root system of woody plants and shrubs, causing root decay and preventing the plant from absorbing necessary water and nutrients, which ultimately leads to death.

The disease affects a wide range of commercially important crops, including Citrus, hop (Humulus lupulus), and avocado. Because the fungus can persist in the soil for several years by colonizing dead organic matter, it poses a significant challenge for long-term orchard and plantation management.

The visual symptoms often begin above ground with leaf yellowing, wilting, and premature drop, followed by dieback of branches. Below the surface, the roots show a dense white to gray mycelial mat. Under the bark of infected roots, characteristic black, string-like structures of the fungus can be observed, which are diagnostic indicators of the disease.

The development of the fungus is favored by high soil moisture, poor drainage, and moderate temperatures. The disease spreads rapidly through root-to-root contact in dense plantings, as well as through the movement of infested soil, contaminated irrigation water, and infected nursery stock.

Managing Rosellinia root rot is difficult because it is often discovered when the plant is already severely damaged. Recommended control strategies include:

• rogueing and burning infected plants including all root fragments;
• improving field drainage and soil aeration;
• applying biological control agents, such as Trichoderma species;
• ensuring the use of disease-free propagation material and maintaining strict quarantine protocols in nurseries.