The previous response here to your question, along with info I also found here at Farmer's ÃÛÌÒÁµÈË, helped me tremendously to (mostly) vanquish the powdery mildew on my peonies. I was surprised to learn that washing down the plants would help. It seems counter intuitive to use water to combat mildew, but it really works! Last season, the lovely foliage on my peonies looked awful, ravaged by mildew. This year, as soon as I noticed the mildew returning, I used a neem oil and water mix spray, coating all the leaves about twice a week. Do this at night. Alternate days that follow nights when you have not used the neem, spray down the plants in the morning so they can sun dry fully later in the afternoon. I use just a gentle shower from a rain spray attachment, no need to get out the pressure washer! Now, at the near end of the season, almost no mildew visible at all, glossy leaves, lovely green. If you notice a leaf cluster getting mildew, remove it. So a fast couple minutes about four times weekly with your peonies will eliminate the mildew. I'm extremely pleased with the advice I got here and the addition of the neem oil spray really seems to make a difference, too. (Bonus: a potted maple sapling that was getting maple fungus has been cured with the neem oil, too!)
The previous response here to your question, along with info I also found here at Farmer's ÃÛÌÒÁµÈË, helped me tremendously to (mostly) vanquish the powdery mildew on my peonies. I was surprised to learn that washing down the plants would help. It seems counter intuitive to use water to combat mildew, but it really works! Last season, the lovely foliage on my peonies looked awful, ravaged by mildew. This year, as soon as I noticed the mildew returning, I used a neem oil and water mix spray, coating all the leaves about twice a week. Do this at night. Alternate days that follow nights when you have not used the neem, spray down the plants in the morning so they can sun dry fully later in the afternoon. I use just a gentle shower from a rain spray attachment, no need to get out the pressure washer! Now, at the near end of the season, almost no mildew visible at all, glossy leaves, lovely green. If you notice a leaf cluster getting mildew, remove it. So a fast couple minutes about four times weekly with your peonies will eliminate the mildew. I'm extremely pleased with the advice I got here and the addition of the neem oil spray really seems to make a difference, too. (Bonus: a potted maple sapling that was getting maple fungus has been cured with the neem oil, too!)