Pink disease

The initial appearance of pink disease involves a thin, white, spider-web-like mycelium growing on the bark surface. As the infection progresses, this growth becomes denser and turns into a characteristic pink or salmon-colored crust.

Infected bark typically cracks and peels away from the wood. In many species, the tree responds by exuding gum, which accumulates in the cracks and around the necrotic areas on the branches.

Leaves on affected branches often turn yellow, wilt, and drop prematurely. Because the fungus often attacks from the top downwards, the dieback of upper canopy branches is a common visual indicator.

If left unchecked, the fungus can spread to the main trunk, which can result in the death of the entire tree. The presence of dense, cobweb-like mycelium is a diagnostic feature used by agronomists to distinguish this from other bark diseases.

• White or salmon-pink mycelial crusts on bark.
• Cracking and peeling bark with gum exudation.
• Premature leaf yellowing and branch dieback.
• Necrotic patches on twigs and major branches.
• Death of the tree if the main stem is girdled.

Pink disease is caused by the basidiomycetous fungus Erythricium salmonicolor, formerly known as Corticium salmonicolor. This pathogen is a significant threat to a wide range of woody plants in tropical and subtropical regions.

The fungus is characterized by its ability to produce several morphological stages, including a white web-like mycelium, pustules, and the distinct salmon-pink crust that identifies the disease. These structures are the primary sources of inoculum.

Infection occurs when spores are dispersed by wind and splashing rain onto vulnerable bark surfaces. Once established, the fungus penetrates the bark and colonizes the cambium layer, effectively girdling branches and twigs.

The pathogen is highly aggressive under favorable conditions, often disrupting the vascular system of the host plant. This leads to the blockage of nutrient and water flow, causing the distal parts of the tree to dry out and die.

Survival of the pathogen is ensured by its presence in infected twigs and branches, making sanitation a crucial aspect of disease management. In warmer climates, it can remain active throughout the growing season.

High humidity and rainfall are the most critical factors for the development and spread of pink disease. The fungus requires moist conditions for spore germination and mycelial colonization of the bark.

The optimal temperature range for the pathogen's growth is between +20°C and +28°C. During warm, humid seasons, the disease can spread rapidly through an orchard, especially if canopy density is high.

Poor aeration within the tree canopy maintains a humid microclimate, which significantly increases the risk of infection. Branches that remain wet for long periods are prime targets for fungal attachment.

Mechanical injuries caused by pruning, insects, or environmental damage provide entry points for the fungus. Bark that has been damaged by sunlight or pests is often more susceptible to colonization.

Excessive use of nitrogen fertilizers promotes lush, succulent growth that is less resistant to fungal penetration. A balanced nutrition program is essential to maintain the structural integrity of the bark and cambium.

Pink disease is economically damaging, primarily because it reduces the productive lifespan of trees. The loss of bearing branches directly leads to decreased yields and long-term orchard decline.

Trees affected by the fungus are often weakened and more susceptible to secondary pests and pathogens. This cumulative stress can lead to the overall loss of tree vigor and eventual mortality.

In large-scale fruit production, pink disease can necessitate the removal of infected trees to prevent an epidemic. This requires significant investment in replanting and orchard rehabilitation.

The disease impacts the quality of fruit as the tree struggles to transport nutrients past the infected bark. This leads to smaller fruit sizes and reduced quality, affecting the marketable value of the harvest.

The risk of rapid spread means that growers must remain vigilant. Without timely intervention, a localized problem can quickly escalate into a widespread orchard issue, threatening regional production.

The primary control measure is the aggressive pruning of infected branches. It is vital to cut well below the visible symptoms into healthy wood to ensure all mycelium is removed.

All pruned materials must be removed from the orchard and burned or buried deep to eliminate the inoculum source. Leaving infected wood on the ground can facilitate further spore dispersal.

Chemical control involving copper-based fungicides is effective when applied as a preventative measure. Applications should be timed before the onset of the rainy season to create a protective barrier on the bark.

Orchard management practices, such as proper pruning for improved air circulation and light penetration, are essential. A well-managed, open canopy dries quickly after rain, making it less hospitable for the fungus.

Strengthening the tree's natural defense through proper fertilization (potassium and phosphorus) and good irrigation practices helps the tree withstand potential infections and heal small wounds more efficiently.