Hydrangea rust

The causative agent of this disease is a specialized fungus from the rust group known as Aecidium hydrangeae-paniculatae. This pathology belongs to the rust disease type, where the fungus primarily attacks the vegetative organs of the plant, disrupting the photosynthesis process and causing premature wilting of tissues.

The main object of infection is the panicle hydrangea (Hydrangea paniculata), which is widely cultivated in ornamental horticulture. In rare cases, the fungus mycelium may also be found on closely related species if microclimate conditions favor the spread of spores.

Symptoms manifest as characteristic structures of the aecial stage of rust: numerous orange-yellow or brownish pustules (aecia) form on the underside of the leaves. Chlorotic spots often form around them, which may become necrotic over time, leading to mass leaf drop.

The development of the pathogen is directly dependent on air humidity levels and temperature. Optimal conditions for spore germination include the presence of water droplets on the leaf surface (dew, fog, precipitation) at moderate temperatures ranging from 18–22 °C. Dense plantings and poor ventilation significantly accelerate the rate of disease spread.

The harmfulness of rust lies in the severe exhaustion of the plant, a decrease in flowering intensity, and the loss of decorative qualities. With severe infection, the hydrangea loses a significant portion of its foliage, which weakens the bush before winter, reducing its overall frost resistance and resilience to unfavorable environmental factors.

• Carry out regular sanitary pruning of infected shoots and collect fallen leaves.
• Maintain optimal spacing during planting to ensure proper air circulation around the bush.
• Avoid overhead watering of plants in the evening to prevent excessive humidity.
• Use copper-based fungicides or modern systemic products for treatment at the first signs of the disease.