Orange rust

Orange rust is a destructive systemic fungal disease caused by the pathogen Arthuriomyces peckianus. This fungus specifically targets plants in the Rubus genus, with blackberries and raspberries being the primary hosts. Unlike localized leaf diseases, this fungus becomes integrated into the plant's vascular system.

The host range is primarily limited to species within the Rubus genus. Because the disease is systemic, the fungus colonizes the plant's crown and roots. This means that once a plant is infected, it remains infected for its entire life cycle, serving as a permanent source of inoculum for surrounding healthy plants.

Symptoms are most visible in early spring. Initially, the leaves appear pale, but they quickly become covered in distinctive, bright orange, powdery pustules. Infected canes often appear spindly, stunted, or lack the typical vigor of healthy growth. By mid-summer, the diseased leaves usually wither and drop, but the fungus remains active inside the crown.

The development and spread of orange rust are highly dependent on cool, damp conditions. The fungal spores are easily dispersed by wind and splashing water. High humidity levels during the spring flush of growth create the ideal environment for the spores to germinate and penetrate the young, developing tissue of the host plants.

The economic impact of this disease is significant, as it leads to complete yield loss and plant decline. There are no curative chemical treatments for systemic orange rust. The only effective management strategy involves early detection, immediate removal of the entire plant (including roots), and strict sanitation to prevent the spread to the rest of the plantation.

• Prompt removal and destruction of infected plants.
• Use of certified, disease-free nursery stock.
• Regular scouting of the garden during spring.
• Spacing plants to ensure better airflow and reduced humidity.