Brown root rot

Brown root rot is a destructive plant disease caused by the basidiomycete fungus Pyrrhoderma noxium (often cited as Phellinus noxius). This pathogen acts as a primary root destroyer, attacking the vascular tissues of woody plants, which leads to structural instability and total loss of nutrient uptake, eventually causing the death of the host tree.

The host range of Pyrrhoderma noxium is exceptionally wide, encompassing hundreds of plant species across diverse families. It is a major economic concern in tropical and subtropical agriculture, severely affecting plantations of rubber trees, coffee, oil palms, and fruit trees, as well as various ornamental trees in urban landscapes.

Symptoms are often progressive and start with canopy thinning, chlorosis, and gradual wilting. A key diagnostic feature is the presence of a distinct brown to black mycelial mat on the collar region of the trunk. As the disease advances, the wood within the roots becomes necrotic and brittle, often displaying a brownish, spongy texture that compromises the tree's ability to remain upright.

The disease spreads primarily through root-to-root contact in the soil and contact with infested wood debris. The fungus can survive for many years as a saprophyte in stumps and large root fragments remaining in the ground after tree removal. High soil moisture and warm temperatures significantly accelerate the growth of the fungal mycelium and its infection potential.

Management strategies focus on eradication and prevention. Effective measures include:

• Complete removal of infected trees including major roots and stumps.
• Ditching around infected sites to prevent root contact between healthy and diseased plants.
• Soil solarization or fumigation in severely affected areas before replanting.
• Application of specialized fungicides to protect healthy seedlings in high-risk zones.

By implementing these strict sanitation protocols, growers can minimize the economic impact and prevent the further establishment of the pathogen within their agricultural plots.