Rhizomorph disease

Rhizomorph disease is a destructive condition caused by fungi of the Armillaria genus, characterized by the development of dark, root-like mycelial strands known as rhizomorphs. These structures allow the pathogen to spread through the soil and infect the roots of susceptible host plants, leading to systemic decline and death.

The host range of this pathogen is remarkably broad, affecting various horticultural and agricultural sectors. Key crops prone to infection include Citrus, strawberry, hop (Humulus lupulus), cassava, avocado, Plane trees, and stone fruits such as sour cherry (Prunus cerasus) and apricot.

Symptoms typically begin with yellowing of the leaves, stunted growth, and canopy thinning. Upon closer inspection, characteristic white mycelial fans appear under the bark near the root collar. As the infection progresses, the wood decays, emitting a distinct mushroom-like odor, while black, shoestring-like rhizomorphs become visible on the root surface.

The development of the disease is highly dependent on environmental conditions, particularly high soil moisture and poor drainage. The pathogen thrives on decaying organic matter, such as old stumps or buried wooden debris, which serve as reservoirs for the fungus, allowing it to bridge gaps between healthy host roots in the soil.

Managing the disease requires a rigorous integrated approach focused on sanitation and soil modification. Key control practices include:

• Complete removal and destruction of infected stumps and root systems.
• Improving soil drainage to minimize conditions favoring fungal growth.
• Implementing root barriers to prevent the contact of healthy roots with infected rhizomorphs.
• Prioritizing the planting of resistant or tolerant cultivars.
• Regular monitoring of tree health to detect early signs of root decay.