Part of the problem with my perennials is that they are sun-loving perennials and I have them in part shade. Therefore, after rains, they do not dry out quickly and leaf spot diseases are showing up.
Leaf spot diseases in perennials are common and many occur under wet conditions, though not all. Typically, they don’t cause much damage other than cosmetic. I don’t worry about them as diseases can be hard to manage.
A common leaf spot disease, Cladosporium paeoniae on peonies showed up earlier this summer and led to symptoms that resembled measles on the leaves. The spots were small, reddish, and coalesced to cause purplish blotches on the leaves and stems.
This was caused by the wet spring and high humidity that we had earlier. Remove the infected foliage and stems this fall and clean up as much debris as possible. I have cut mine back as early as mid-August (now) and they do fine the next year.
The only way to control this is to have a fungicide on it early in the spring before the symptoms develop. The problem with that is many fungicides are washed off by rain, presenting a huge challenge for gardeners.
Leaf spots such as this won’t kill plants but infection season after season can diminish the quality of the plant.
Right now, I am seeing leaf spots on several perennials, caused by a variety of fungi. I repeat it’s too late to spray a fungicide for leaf spots when you see them. These are the symptoms that are a result of a causal agent (i.e., fungi, bacterial, virus, etc.)
Since they don’t kill the plants, try to keep the root systems healthy. If your plants are in a wet area and the roots don’t dry out, they may end up with one of the water mold diseases.
Credit: Contributed
Credit: Contributed
Unfortunately, these do kill plants. The most common water mold diseases in perennial gardens are Pythium spp. and Phytophthora spp. These fungal-like organisms move easily through water, therefore as soil remains wet, they spread quickly.
These tend to be host-specific. One that you are familiar with is the Phytophthora that was the cause of the potato blight in Ireland.
The only way to control these in the garden is to plant in the right location and avoid consistently wet soils. If plants get Pythium or Phytophthora, the only solution is to rogue them (remove them).
My sun-loving perennials planted in part shade are losing foliage to leaf spot disease. Other than looking awful, I am not worried about them as they will come back next season.
Pamela Corle-Bennett is the state master gardener volunteer coordinator and horticulture educator for Ohio State University Extension. Contact her by email at bennett.27@osu.edu.
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