Brownish-purplish blotches have appeared on the leaves of my peonies. Actually, they get a few blotches every year, but this summer it looks worse. Googling “brown blotches on peony leaves” brought forth a frightening list of every peony ailment known to man. Peony botrytis seemed to be at the top of the list, and photos of afflicted peonies did look miserably similar to mine. Or was it Phytophthora blight, which also caused ugly blotches? Both of these are serious fungal infections. By a lucky chance, I stopped by the Pure Gardener Nursery in Geneva yesterday to purchase a birthday present, and I asked the owner about my peonies, and whether he knew of an organic fungicide. He pointed out that botrytis can cause bud blasting and stem damage beginning in the spring and that grey mold is visible, and felt that my peonies didn’t have anything so serious. He recommended a fish oil spray, and also showed me a powdered copper fungicide. I opted for the fish oil spray because it is easy to apply and also has nutritive value.
Back at home, I did further investigation and found there is another peony fungal infection called peony leaf blotch. This poses more of a cosmetic problem than anything. Peony leaves with leaf blotch will have some measle-like spots, and the brownish blotches are a light brown on the other side of the leaf. All the roads of my investigation led to one control of peony fungal problems–sanitation. Fungal spores accumulate on the soil and dead vegetation around the peony. When new peony shoots emerge in the spring, they are contaminated by the spores, which also splash up on the plant during spring rains. So meticulous fall cleanup of peonies is a must. I also came across a variety of suggestions for covering the soil around the peony with limestone chips or sand. I’ll see what the fish oil spray does first.
For more on preventing peony fungal diseases, this link from the Univ. of Minnesota is helpful: http://www.extension.umn.edu/distribution/horticulture/DG1153.html. Also, I ran across a service at Iowa State University called a Plant & Insect Diagnostic Clinic. For a fee, you can send them an insect or sick leaf, and they can tell you what the problem is. Their website is at http://www.ent.iastate.edu.pidc/.
Since my peony leaf blotch problem is mainly cosmetic, I will treat with the fish spray and live with it. If my peonies looked like those on the right, which are part of a long, neglected row of plants I pass on the way to work, I would cut them down to the soil and burn the leaves. I might dig some plants up and dispose of them because they are too close together. Then I would treat with a fungicide.
Speaking of peony leaf problems–guess what this is? Hail damage! We had a big hail storm last Saturday afternoon and many plants were left pock-marked. It’s always something!