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Peony Diseases

Peonies have relatively few diseases. The most common one is botrytis. An excellent online article on peony diseases with photography can be found at the Canadian Peony Society.

Lemoine Disease

Lemoine Disease is a serious disease of peonies. Fortunately, it appears to be uncommon. During their first visit to the property in spring 2009, the Peony Advisory Board discovered Lemoine Disease infecting just over 10% of the peonies. Lemoine Disease is suspected to be caused by a virus. This disease severely reduces foliar growth, stunts and causes gnarled irregularities to form on the roots, and ultimately prevents the peony from flowering. There is no known cure. The disease is spread through peony sap. This happens when shovels or pruners used on a diseased plant are subsequently used on a healthy plant, thus infecting it. Luckily, we can control the spread of the disease by sterilizing our tools between plants when we prune or dig. To date there is no evidence that sucking insects (as aphids) spread the disease.

From 2009 to 2012, all the plants were reviewed for Lemoine Disease, facilitated by our Peony Advisory Board experts. All symptomatic plants have been removed to a quarantine nursery several miles/kilometers away for long-term monitoring. Since some of these diseased specimens are believed to represent otherwise extinct cultivars we are keeping them for now. At a future date there may be found a means to tissue culture and regenerate disease-free plants.

Empty spaces reflect intentional plant removals

In fall 2009, over 70 peonies with Lemoine Disease were removed to a quarantine facility. Since then, additional symptomatic plants have been removed. The spaces where the peonies were removed are left void of peonies for at least one year to make sure that no roots were left behind to sprout and to allow time for us to rejuvenate the soil. Cover crops of winter wheat and annual rye are planted in the empty spaces to improve soil quality and structure throughout the fall and winter season. In the spring the cover crops are mowed and tilled under to act as a green manure, adding organic matter to the soil. All these steps are part of a disease management program to improve the garden soil and prevent future disease problems.
In addition, desired historic peony cultivars are being planted in the garden to diversify our collection. Since some of the existing cultivars are overly duplicated they are removed for the 'new' plantings one year in advance. This activity also generates empty planting spaces. During the fallow year, the soil is improved.
Some historic annuals of the early twentieth century have been planted in the empty spaces to add beauty to the garden reminiscent of the era of the peonies and to act as a cover crop until the desired peonies can be replanted.
Learn about historic annuals in the Peony Garden.