White root rot

The causal agent of white root rot is the fungus Rosellinia necatrix (also known as Dematophora necatrix). This soil-borne pathogen causes a destructive root decay that impairs the plant's vascular system, preventing the uptake of water and nutrients and ultimately leading to sudden wilting and tree death.

The disease affects a vast range of hosts, including pome fruits like the apple tree (Malus domestica), stone fruits, grapevines, and various woody ornamental species. Its broad host range makes it a significant threat in diverse horticultural environments, often spreading rapidly in orchard settings.

Symptoms initially manifest as chlorosis, stunted growth, and premature leaf drop. The diagnostic sign is the presence of white, cottony mycelial fans under the bark of the roots and the crown. As the disease progresses, the cortical tissue of the roots turns black and necrotic, often emitting a distinct fungal odor.

Development is highly favored by damp, poorly drained soils and cool to moderate temperatures. The pathogen spreads through mycelial contact between roots and can persist for long periods in the soil as sclerotia, making it extremely difficult to eliminate once it has established a foothold in an orchard.

Effective management focuses on prevention, including selecting well-drained planting sites and ensuring only pathogen-free stock is used. If infected trees are identified, they must be removed with their entire root system. Soil solarization or chemical fumigation may be required, followed by a waiting period before replanting to ensure the pathogen has been eradicated.