From our perspective as peony plants, Botrytis blight, often called gray mold, is a devastating and suffocating invasion. It begins subtly, often as a small, water-soaked lesion on a young, tender shoot emerging from the soil in spring. This spot is not just a mark; it is a point of decay where the fungal pathogen *Botrytis paeoniae* is actively consuming our tissues. We feel our structural integrity weakening at these points. The lesion rapidly expands, turning dark brown or black, and often causes the stem to wilt and collapse entirely, a condition you call "stem rot." This cuts off the vital flow of water and nutrients from our roots to the rest of our system.
The attack is not limited to our stems. The fungus can spread to our leaves, where it creates large, irregular brown patches. These patches are areas where we are dying; our photosynthetic machinery is being destroyed, robbing us of the energy we need to grow and bloom. The most heartbreaking manifestation is on our flower buds. A prized bud we have worked all season to produce can suddenly turn brown and become covered in a fuzzy, grayish-brown mold. This mold is the reproductive structure of the fungus, releasing countless spores into the air to infect our neighbors and return to us next season. The bud will then either dry up and become mummified or rot away completely, denying us our reproductive purpose.
We peonies thrive in conditions that are quite the opposite of what this pathogen loves. We desire well-drained soil and plenty of sunlight and air circulation around our canopies to keep our foliage dry and robust. The fungus, however, exploits any weakness. It thrives in the cool, damp, and crowded conditions that sometimes occur around us. Prolonged periods of leaf wetness from rain, overhead watering, or heavy dew are its primary weapons. It enters through wounds or directly penetrates our tender, young growth, and once inside, it rapidly breaks down our cells.
The most effective way to help us fight this blight is through your cultural practices. Please ensure we are planted in a sunny location with ample space between each plant to allow air to flow freely through our leaves, drying them quickly after rain. In autumn, when we retreat into dormancy, it is crucial to cut our stems back to ground level and remove all foliage and plant debris from the garden. Do not compost this material, as the fungus can overwinter there. This sanitation removes the primary source of infection for the next spring, giving our new shoots a clean start. Also, avoid applying high-nitrogen fertilizers, which promote the soft, succulent growth that is most vulnerable to infection.
When environmental conditions are persistently favorable for the disease, even the best cultural practices may not be enough to protect us entirely. In such cases, a protective fungicide applied as our new shoots emerge from the soil in early spring can create a critical barrier. This barrier helps shield our vulnerable young tissues from the germinating fungal spores. It is a preventative measure, not a cure for an existing infection. Please always follow label instructions carefully to ensure it is applied in a way that helps us without causing harm.
