From our perspective as peonies, Botrytis cinerea is a relentless fungal foe that thrives in the very conditions we find challenging: high humidity and poor air circulation. The fungus attacks our tender new shoots in spring, appearing as a dark, fuzzy mold that causes them to wilt and collapse. It then progresses to our flower buds, which may turn black and fail to open, or it can leave unsightly brown spots on our open blooms and leaves. This weakens us significantly, depleting our energy reserves meant for next year's growth.
Our first and most crucial line of defense is superior cultural care. You can help us immensely by modifying our immediate environment. Please ensure we are planted in a location with maximum sunlight exposure and excellent air movement; this helps our foliage dry quickly after dew or rain. Avoid crowding us with other plants. When watering, please direct the water to our base and soil, not onto our leaves and flowers. Overhead watering creates the prolonged leaf wetness the fungus needs to germinate and invade our tissues.
Sanitation is non-negotiable for our survival in a humid climate. In fall, after our foliage has died back, you must cut our stems down to ground level. Every single piece of leaf and stem debris must be removed from the garden and destroyed—do not compost it. The fungus overwinters in this debris and in the soil, waiting to attack again in spring. Throughout the growing season, be vigilant. At the first sign of any infected material (wilting stems, spotted leaves), prune it out immediately. Sterilize your cutting tools between each cut to prevent spreading the spores to healthy parts of our structure.
When humidity is persistently high, cultural practices alone may not be enough to protect us. In these cases, a preventive fungicide program acts as a vital protective shield. Please begin applications in early spring as our red shoots first emerge from the soil. Focus on covering all surfaces of our new growth. Continue applications according to the product's label through the flowering period, especially if wet weather is forecast. It is imperative you rotate between fungicides with different active ingredients (e.g., chlorothalonil, mancozeb, iprodione) to prevent the Botrytis fungus from developing resistance.
Our long-term vitality is your best defense. Avoid high-nitrogen fertilizers, which promote the succulent, soft growth that is most susceptible to infection. Instead, use a balanced fertilizer to encourage strong, resilient growth. For future plantings, we advise you to seek out peony cultivars noted for their stronger resistance to fungal diseases. While no variety is completely immune, some are significantly less prone to severe Botrytis outbreaks, which will lead to a healthier, more beautiful garden with less intervention.
