Q: My peony has weird yellow rings on the leaves on one side of the plant. Is it serious? Would it help to remove those leaves?
A: It is a virus, probably one called tobacco rattle virus. It used to be called peony ringspot or peony mosaic virus, which are very descriptive of the problem. There are a couple of other viruses possible, but to positively identify which one you have you would need to send a sample to a lab, and it probably won’t change your treatment options.
TRV was first identified in tobacco, but it can affect 400 kinds of plants, from tulips to chickweed. Many of these plants don’t show any effect of the virus and it stays only in the roots. With others, it can also show in the leaves. Potatoes can get dark spots in the tuber. It doesn’t affect peony flowers, but sometimes the plant can be stunted or just not grow well.
Although only part of your plant is showing symptoms, the whole plant is affected, so removing the yellow sections won’t do any good. Symptoms are more apparent in cooler weather, but the virus is still there even if the leaves look fine. You may see the same symptoms next year or not, but there is no cure.
TRV is spread by nematodes. They feed on the roots of an infected plant and then transmit the virus when they move to the next plant. Since many plants that we consider weeds are vectors, removing them is helpful. Shovels and other tools that touch the plant roots should be disinfected.
If the plant is otherwise healthy, no treatment is necessary. In fact, the leaves can look very cool. But, if you have potatoes or prized plants nearby, you may want to remove it to prevent the virus from spreading. You can plant something new, even another peony, in the spot immediately as the virus does not live in the soil, only in the plant roots. However, if there are still plants nearby that are hosting the virus it will likely be spread again by those pesky nematodes.
Written by U of M Extension Master Gardeners in St. Louis County.