Cushion gall

Cushion gall is a significant fungal disease caused by the pathogen Nectria rigidiuscula (often identified as the teleomorph state of Calonectria rigidiuscula). This disease is a major concern in cacao production, specifically targeting the woody parts of the tree and impacting overall orchard health.

The primary host for Nectria rigidiuscula is the cacao tree (Theobroma cacao). The fungus typically acts as a wound parasite, meaning it enters the plant through existing injuries in the bark, pruning scars, or damage inflicted by sucking insects such as mealybugs and scale insects, which serve as common vectors for the pathogen.

Symptoms are characterized by the development of abnormal, tumor-like outgrowths known as galls. These growths appear as dense, cushion-shaped swellings on the bark of stems and branches. These galls can eventually coalesce, leading to severe deformity of the branches and disruption of the vascular system which transports nutrients throughout the tree.

Development and spread of the disease are heavily influenced by environmental factors such as high humidity and rainfall. Rain splashes and wind play a crucial role in dispersing fungal spores across the plantation. Furthermore, the close association between the fungus and bark-damaging insects facilitates the efficient transmission of the pathogen to healthy tissues.

The economic impact of cushion gall is significant, as infected trees often show reduced vigor, stunted growth, and a substantial decline in bean production. In cases of severe infection, branches may become brittle and break off, or the tree may eventually die, necessitating the removal of the affected individual to protect the surrounding plants.

Integrated management practices for prevention include:

• Routine removal of infected galls and pruning of damaged branches to eliminate inoculum sources.
• Sterilization of pruning tools using appropriate disinfectants to prevent cross-contamination.
• Management of insect populations that cause bark damage, thereby preventing entry points.
• Maintaining proper spacing and canopy management to ensure air circulation and reduce humidity levels around the stems.
• Protecting large wounds with fungicidal pastes to prevent fungal colonization after maintenance pruning.