Scout your newly planted peonies to ensure they are virus-free.

One of the great pleasures of our job is to work with peony growers as they establish their new fields. Perennial crops, such as peonies, are large investments which take years of care before the first harvestable crop. Even though growers likely won’t be selling any out of their field for the first two or three years, this time period is critical for disease management.

One of the most important diseases to scout for during this time period is Tobacco Rattle Virus (TRV). Despite its name, TRV has a very wide host range and is one of the most common viruses to affect peonies. It has been reported on peonies in Asia, Europe, New Zealand, and North America. In our surveys of peonies from 2014-2016, in part supported by an ASCFG Research Foundation Grant, we have observed peony plants with TRV symptoms from Washington, Oregon, Alaska, South Carolina, New York, and the Netherlands.

In most cases, TRV is introduced into newly planted peony fields on rootstock. Although most rootstock producers are careful to rogue (remove) infected plants from the field, detection of the virus is sometimes difficult and infected plants can be divided and sold. As such, it is not uncommon to have a few plants in a rootstock lot infected with TRV. If the majority of a rootstock lot is infected with TRV, this may be an issue to address with the supplier. 

It is critical for growers to identify plants that have potentially entered the field infected with the virus to limit its impact on the future harvestable product.

TRV on peony has also been referred to as “peony ringspot virus” or “peony mosaic virus,” which describe the alternating yellow and green concentric ring pattern, and yellow and green stippling or blotching of the leaves, which are characteristic symptoms of this disease. It can also be expressed as yellow banding or chevron patterns across the leaf. In some conditions, these symptoms can appear more orange or purple. These symptoms, if apparent during cutting, can render stems unmarketable. There are no visible symptoms on the flower nor are studies available on how the virus affects flower quality or yield.

Symptom expression of TRV is highly dependent on cultivar and environmental conditions. As with other viruses, TRV symptoms can disappear during certain times of year. Due to the transient nature of TRV symptoms, symptomatic plants should be tagged so the plant can be identified later if symptoms fade. Although symptoms may no longer be expressed, the plant is still infected with the virus. Furthermore, even if only a few parts of the plant are showing symptoms, the plant is systemically infected—all plant parts contain the virus. There is no way of “cutting out” or curing a peony of TRV.

Even in the absence of visible symptoms, the virus can move from plant to plant by nematodes, microscopic soil-dwelling roundworms, in the genera Trichodorus and Paratrichodorus. There is also some risk of TRV to be mechanically transmitted to healthy plants by contaminated tools that have previously been used on an infected plant, however, this method of transmission is not well understood in peony.

Given the risk of transmission to healthy peonies, management recommendations usually involve rogueing infected plants and replacing them with virus-free material, especially where the nematode vector is known to be present. Early detection means removing diseased plants prior to investing multiple years of care, after which the plant becomes more valuable and it is producing a harvestable product. Some growers may choose to leave a plant infected with TRV, especially in areas where the vector is not present. In this case, sterilization of hand tools with broad spectrum disinfectants, such as 10% Clorox regular bleach, or dipping tools in a 20% solution of nonfat dry milk between infected and healthy plants may help to prevent the mechanical spread of TRV.

If you have a question regarding whether or not your peonies may be infected with TRV, feel free to contact Andrea or Gary by email with photos of the plant(s) of concern. TRV diagnostics are available through many commercial agricultural testing facilities. Follow our peony disease research at: https://www.facebook.com/WSUpeonies

Affected plants show a range of symptoms on their foliage.

Andrea Garfinkel

Graduate Student

Andrea Garfinkel is a graduate student in Washington State University Puyallup Research and Extension Center, Puyallup. Contact at [email protected]

Gary Chastagner

Professor

Gary Chastagner is Professor, Department of Plant Pathology, Washington State University Puyallup Research and Extension Center, Puyallup. Contact at [email protected]