Aquilegia powdery mildew

The causal agent of this disease is the obligate parasite Erysiphe aquilegiae, a fungus belonging to the Erysiphales order. This pathogen is highly specialized, primarily targeting plants within the Ranunculaceae family. It develops as a superficial mycelium, attaching to the plant surface and drawing essential nutrients through haustoria that penetrate the epidermal cells of the host.

The primary hosts for this fungus are plants in the Aquilegia genus, commonly referred to as columbines. While the infection is most visible on these ornamental species, the fungus can also affect related genera within the family, making it a recurring issue in perennial flower borders and nurseries that grow a variety of Ranunculaceae.

Symptoms typically manifest as a dusty, white-to-grayish mycelial growth on the upper and lower leaf surfaces, petioles, and stems. As the infection progresses, leaves may become distorted, chlorotic, and brittle, often leading to premature leaf drop. Severe infections significantly reduce the plant's aesthetic value and prevent proper flowering.

Disease development is favored by warm days and cool, humid nights, conditions that encourage rapid conidial production and dispersal. Erysiphe aquilegiae overwinters as cleistothecia in plant debris, which release ascospores in the spring, starting the infection cycle anew. Poor air circulation and overcrowding are critical factors that exacerbate the spread of the pathogen.

The impact of this disease on plant health includes a significant reduction in photosynthetic capacity and overall vigor. To mitigate the damage, a combination of cultural and chemical strategies is required:

• Improve air circulation through proper plant spacing.
• Practice strict sanitation by removing and disposing of infected plant material.
• Apply fungicides containing sulfur, triazoles, or strobilurins preventively.
• Avoid overhead irrigation to keep foliage dry, especially in the evenings.