Armillaria root rot

Armillaria root rot, caused by the fungus Armillariella mellea (honey fungus), is a destructive plant disease affecting a wide range of woody plants. It functions as both a pathogen and a saprophyte, surviving on decaying wood while actively colonizing the root systems of weakened trees and shrubs.

The host range for this fungus is extensive, covering various orchard species and plantation crops. Notably, it affects cacao, where it is often referred to as "collar crack" due to the specific damage patterns observed at the base of the stem. The disease significantly impacts agricultural yields and plantation longevity.

Symptoms of the infection include chlorosis, sparse foliage, and gradual crown dieback. A key diagnostic feature is the presence of white mycelial fans beneath the bark at the root collar. In advanced stages, dark, shoestring-like structures known as rhizomorphs develop, enabling the fungus to spread through the soil from host to host.

Favorable conditions for the development of Armillaria include high soil moisture levels and the presence of buried infected stumps or root debris. The fungus spreads via its rhizomorphs or wind-borne spores produced by the mushroom fruiting bodies, which appear near the base of infected hosts during moist periods.

The severity of the disease is high, as it can kill established trees within a few seasons if not managed. Essential control and prevention strategies include:

• thorough removal of stumps and infected tree roots from the soil;
• isolating infected areas with physical barriers or deep trenches;
• maintaining good soil drainage to reduce environmental stress;
• promoting overall plant health through balanced fertilization and irrigation;
• regular monitoring for early signs of mycelial growth on trunks and roots.