Botrytis blight, caused by the fungus Botrytis cinerea or Botrytis paeoniae, is a common disease affecting peonies. From the plant's perspective, this pathogen thrives in cool, humid conditions, attacking tender shoots, buds, leaves, and stems. The fungus invades plant tissues, causing browning, wilting, and decay. Peonies, as perennial plants, are particularly vulnerable during wet springs or when foliage remains damp for extended periods.
Peonies exhibit several signs of Botrytis infection. Young shoots may turn black and wilt suddenly. Buds may fail to open, becoming brown and covered in gray mold. Leaves develop dark, water-soaked spots, while stems show cankers or lesions. In severe cases, the entire plant may collapse. The fungus also produces spores that spread easily, exacerbating the infection.
From the plant's standpoint, prevention is critical. Ensure proper spacing (3–4 feet apart) to improve air circulation. Avoid overhead watering to keep foliage dry. Remove and destroy infected plant debris in fall to eliminate overwintering spores. Mulch lightly to reduce soil splash, which can spread the fungus. Plant peonies in well-drained soil and full sun to discourage fungal growth.
Prune peonies in early spring to remove dead or weak stems, as these are entry points for the fungus. Sterilize pruning tools between cuts to prevent cross-contamination. After blooming, deadhead spent flowers to reduce moisture retention and spore production. In fall, cut back foliage to ground level and dispose of it away from the garden.
If cultural methods fail, fungicides can help. Apply copper-based or chlorothalonil sprays at bud break and repeat every 7–10 days in wet weather. Organic options like neem oil or potassium bicarbonate may also suppress fungal growth. Always follow label instructions to avoid harming the plant or beneficial organisms.
Healthy peonies resist Botrytis better. Fertilize lightly in spring with balanced, slow-release nutrients to avoid excessive soft growth. Avoid high-nitrogen fertilizers, which promote lush foliage prone to infection. Incorporate compost to improve soil structure and microbial activity, which can outcompete pathogens.
Regularly inspect peonies for early symptoms. At the first sign of Botrytis, remove affected parts immediately and apply fungicides if needed. Isolate severely infected plants to protect nearby specimens. Early action minimizes stress on the plant and reduces the need for aggressive treatments.
Rotate planting locations every few years to disrupt the fungus's life cycle. Choose Botrytis-resistant peony cultivars, such as 'Festiva Maxima' or 'Sarah Bernhardt'. Maintain overall garden hygiene to reduce fungal reservoirs. By combining these strategies, peonies can thrive despite Botrytis pressures.
