Red algae

In agronomy, the term Rhodophyta is often associated with parasitic algae that cause leaf spot diseases, most notably represented by the genus Cephaleuros. These organisms are not true pathogens in the traditional sense of fungal infection, but they act as parasitic colonizers of plant tissues, leading to significant physiological stress in the host plant.

These algae primarily affect woody crops and ornamental species in tropical and subtropical regions. Key hosts include citrus, coffee, tea, avocado, and various broad-leaved trees. The algae infect the leaf surface, embedding themselves into the epidermis and absorbing nutrients, which disrupts the normal metabolic processes of the leaf.

The primary symptoms are the appearance of circular, velvety spots on the leaf surface. Initially, these spots are greenish or grey, but as the algae mature and produce reproductive structures, they turn a distinct reddish-brown or rust-like color. Severe infections cause extensive defoliation, stunted growth, and the development of necrotic lesions on woody stems and twigs.

The disease thrives in environments characterized by high humidity, frequent rainfall, and stagnant air. These conditions are ideal for the release and dissemination of motile spores. Poor orchard management, such as dense canopy growth and lack of sunlight penetration, exacerbates the spread of the disease, making it difficult to control without proper canopy maintenance.

The economic damage caused by this disease is significant, as it leads to reduced yields and lower fruit quality due to the loss of functional leaf area. Effective prevention and control strategies include:

• Regular pruning to ensure good light penetration and air circulation.
• Removal and destruction of infected plant debris to reduce inoculum sources.
• Application of copper-based fungicides to inhibit algal development.
• Maintaining proper irrigation schedules to avoid creating unnecessary surface moisture on foliage.