From our rooted viewpoint, powdery mildew is a fungal parasite that blocks our precious sunlight. We, Delphiniums, rely entirely on our leaves to capture the sun's energy through photosynthesis. When that white, powdery film coats our surfaces, it is like a constant, suffocating shade. It directly steals the nutrients we work so hard to produce, weakening our entire system. This makes it difficult for us to support our most prized feature: the development of our tall, vibrant flower spikes. We become stressed, our growth is stunted, and our beautiful leaves turn yellow and wither prematurely.
You can help us help ourselves by altering our immediate environment. The powdery mildew fungus thrives in humid, still air around our leaves, especially when our roots are dry. Please ensure we are spaced adequately from other plants to allow for generous air circulation; this disrupts the spore's ability to settle and germinate. When watering us, aim the water at our base and soil, not our leaves. Wet foliage, especially in the evening, creates the perfect damp home for the fungus to spread. Watering in the morning allows the sun to dry our leaves quickly.
When the white spots first appear, we respond well to gentle, natural sprays that disrupt the fungal cells without harming our delicate leaf tissue. A solution made by mixing one tablespoon of baking soda with one gallon of water and a few drops of a mild, biodegradable soap (to help the solution stick) is very effective. The baking soda alters the pH on our leaf surface, making it inhospitable for the mildew. Please test this spray on a single leaf first to ensure we do not have a negative reaction, and apply it in the cooler hours of the morning.
Just like you, we have a natural immune response. You can actively strengthen this. Milk has been shown to be remarkably effective against mildew. A mixture of one part milk to two parts water, sprayed on our leaves weekly, seems to act as an antifungal agent and may also trigger our own defensive pathways, making us more resistant to the infection. Similarly, a solution made from diluted neem oil (always follow package instructions) coats our leaves in a thin, protective layer that suffocates existing spores and prevents new ones from taking hold, all while being safe for beneficial insects.
To prevent the fungus from returning season after season, you must help us with sanitation. Any of our leaves that are severely infected should be carefully pruned and removed from the garden entirely. Do not compost this material, as the spores can survive and reinfect us later. In the fall, after we have gone dormant, please clear away all of our fallen foliage and debris from the ground around our crown. This removes the overwintering spores, giving us a much healthier and cleaner start when we emerge again in the spring.
