Chrysanthemum ascochyta blight

Chrysanthemum ascochyta blight is a severe fungal disease caused by the pathogen Stagonosporopsis chrysanthemi. This disease primarily affects chrysanthemums, causing significant damage in both greenhouse environments and garden beds, potentially leading to total loss of flowers if left unmanaged.

The symptoms of the infection typically appear as dark brown or black necrotic lesions on the leaves, stems, and flower buds. As the infection progresses, these spots expand, causing the affected parts of the plant to wither and dry out. In high humidity, tiny black fruiting bodies known as pycnidia develop within the lesions, releasing spores that continue the infection cycle.

Environmental conditions play a critical role in the development and spread of the blight. The fungus thrives in warm, humid weather and is easily disseminated by splashing water, rain, air currents, and contaminated gardening tools. The pathogen is capable of surviving for long periods in plant debris, infected soil, or infected cuttings, making sanitation a cornerstone of management.

The economic impact of this disease is significant, particularly in commercial cut flower production. Besides the aesthetic degradation caused by unsightly leaf spots and distorted blooms, the disease can cause stem girdling, which results in the wilting and death of the entire plant. Heavy infestations reduce the yield and quality of marketable flowers drastically.

Management strategies focus on a combination of cultural practices and chemical control. Growers should ensure optimal ventilation in greenhouses to reduce moisture, avoid overhead irrigation, and promptly rogue out infected plants. Fungicide applications, particularly those containing systemic active ingredients, are recommended during periods of high disease pressure to protect the crop effectively.

• Select resistant chrysanthemum cultivars when possible.
• Maintain strict sanitation practices in the greenhouse.
• Use drip irrigation to keep foliage dry.
• Remove and destroy all infected plant material immediately.
• Apply preventative fungicides as part of an integrated pest management program.