Powdery mildew of chrysanthemum

The disease is caused by the fungus Oidium chrysanthemi, a common plant pathogen known for forming white, powdery colonies on the aerial parts of host plants. This fungus acts as an obligate parasite, extracting nutrients directly from the epidermal cells of the plant, which severely stresses the metabolism and development of the chrysanthemum.

The primary host for this pathogen is the chrysanthemum species, although it can affect various cultivars in both indoor and outdoor environments. Greenhouse cultivation is particularly prone to outbreaks, as the environment provides a stable, protected habitat for the fungal spores to colonize and spread rapidly across dense plant populations.

Typical symptoms include the appearance of white, dust-like spots on the foliage and stems. As the infection progresses, these spots coalesce, covering the entire surface of the leaf. This results in yellowing, stunted growth, leaf curling, and eventually necrosis, which significantly detracts from the plant's aesthetic value and health.

Environmental conditions play a crucial role in the development of Oidium chrysanthemi. High humidity, poor airflow within the foliage canopy, and mild temperatures are the main triggers for spore germination. In commercial production, crowded plant spacing and lack of ventilation often exacerbate the spread of the disease.

Effective management requires a combination of good sanitation practices and chemical intervention. Because the fungus can persist on plant debris, removing and destroying infected material is vital to reduce inoculum levels. Integrating preventative fungicide sprays with proper cultural management is the most successful approach to keeping plants healthy and vigorous.

• Maintain proper spacing between plants to enhance air circulation.
• Remove and destroy all infected foliage immediately.
• Apply preventative fungicides based on local guidelines.
• Ensure the greenhouse environment has consistent humidity control.
• Select resistant cultivars to minimize the risk of infection.