Hosta Virus X

Hostas have a great reputation for being pest and disease free. Other than foliar nematodes, gardeners could buy and trade hostas and not have to worry about bringing anything harmful into their garden. Unfortunately, this has changed. Not only are foliar nematodes out of control, but recently a disease has spread through the market place like wildfire.

Starting about 1998-2000, a few "lucky" hosta growers began finding what appeared to be new, interesting sports of otherwise common hostas. These "sports" showed blue or green colored spots or blotches throughout the gold part of the leaf. While some people thought it was beautiful, others found it disturbing. A few individuals became especially concerned when these oddly marked plants began showing up in great numbers over the next couple years at many of the big chain stores and nurseries.

Dr. Ben Lockhart, of the University of Minnesota, discovered the cause of this mottled coloring: Hosta Virus X (HVX). It is unclear exactly where Hosta Virus X came from, but it is very clear that it has quickly reached epidemic proportions.

Symptoms of Hosta Virus X

Hosta Virus X affects different hosta cultivars in different ways, so it is impossible to give a definitive description of symptoms. The most common visual symptom is blue or green markings on a light colored leaf. These markings usually follow the leaf veins and bleed out into surrounding tissue giving the plant a mottled appearance. The tissue often appears lumpy, puckered, and of different thickness or texture that normally colored tissue. Less common symptoms include dried, brown spots and twisted, deformed leaves. It may be difficult to detect off colored mottling on dark, solid colored leaves. Some green tissue will show lighter colored mottling along the veins, but it is often not as pronounced as the markings on gold tissue. Some dark colored Hostas appear as if they have had bleach spilled on them, though. To make matters worse, some hosta cultivars don’t seem to show any visible symptoms of being infected with HVX and it may take a year for symptoms to show after a plant has been infected.

Hosta 'Gold Standard' infected with Hosta Virus X Photos courtesy of Rich Horowitz

Hosta 'Striptease' infected with Hosta Virus X Photos courtesy of Jim Soper		Hosta 'Striptease' infected with Hosta Virus X Photos courtesy of Luke Schmidt

Hosta 'Birchwood Parky's Gold' infected with Hosta Virus X Photos courtesy of Jean	Hosta 'Royal Standard' infected with Hosta Virus X Photos courtesy of Jean

Method of Infection

The most obvious way for Hosta Virus X to spread is by sap from an infected plant being mechanically transferred to another plant. Unfortunately, this is easier done than one might think. Contaminated tools and hands can both spread the disease. Cutting roots while digging and trimming off damaged leaves and spent flower scapes can easily transfer infected sap to healthy hostas. Researchers say the virus can not be spread by insects, but when we are talking about moving sap from one plant to another, I don't see how you can rule out insects completely. Or other animals like rabbits and deer, for that matter.

TC is not the cause of this epidemic. HVX can survive the tissue culturing process, but most tissue culture labs screen their stock plants for multiple viruses before putting them into TC. The main source of the Hosta Virus X epidemic is several large wholesale growers in Holland and a couple here in the US who have it in their growing fields. It is during the harvesting process that the virus is spread. Not only through digging and cutting, but many of the overseas growers power wash the plants in preparation for export. During this process, some of the outer layer of tissue is actually stripped off exposing sap that can infect other plants through their stripped tissue.

We are only just beginning to understand how Hosta Virus X works. While mechanical infection poses the biggest risk, researchers may discover other means by which HVX spreads. There is no cure for plant viruses and it is not safe to have virus infected hostas in our gardens.

There are no known cases where Hosta Virus X has been passed on to seedlings via pollen or seed. Other viruses closely related to HVX are proven not to transfer via seed, so it is expected that HVX behaves in the same manner.

Photos courtesy of Carol Brashear

Preventing Hosta Virus X from Spreading

The best way to prevent Hosta Virus X from infecting your collection is to simply not grow infected plants. Always avoid strangely spotted or mottled plants you find at nurseries. Not all infected plants show visible symptoms, though, so if one plant in a group shows symptoms do not buy healthy-looking plants in the same group. If one has it, it is very possible some, and maybe all, of the others do. Any plants that came from the large bulk wholesalers should be considered "on probation" for the next two years. This includes most hostas found at the "big box" stores. Watch for signs of HVX, don't cut them, and throw them out if any suspicious symptoms appear. Whenever you are dividing or trimming plants, always sterilize your tools using bleach, rubbing alcohol, or ammonia between each plant.

Susceptible Varieties

The following hosta varieties have tested positive for Hosta Virus X. The plants tested came from different growers and collectors. This DOES NOT mean all plants of these varieties are infected with HVX, only that some plants of these varieties have been infected and circulated through the market. By far the most commonly encountered infected variety is 'Gold Standard'. It appears from research that some hosta varieties, one being 'Sagae', are showing resistance to being infected with Hosta Virus X. However, it is too early in the game to say with certainty that any hosta variety is completely resistant.

Photos courtesy of Carol Brashear

• 'Birchwood Parky's Gold'
• 'Blue Cadet'
• 'El Nino'
• 'Fan Dance'
• 'Gold Edger'
• 'Gold Standard'
• 'Golden Tiara'
• 'Goldrush'
• 'Halcyon'
• 'Little Aurora'
• 'Paradise Joyce'
• 'Royal Standard'
• 'Stiletto'
• 'Striptease'
• 'Sun Power'
• 'Sum & Substance'
• 'Sweet Home Chicago'
• 'Undulata Albomarginata'

Hosta 'Sum and Substance' infected with Hosta Virus X Photos courtesy of Thomas Barnard

Hosta 'Sweet Home Chicago' infected with Hosta Virus X Photos courtesy of Vicki Hickman

Before much was known about viruses in hostas, some infected plants were given names. All plants of these varieties ARE infected with a virus. Some are infected with Hosta Virus X, some may be infected with other viruses.

Hosta 'Breakdance' showing typical Hosta Virus X symptoms.

• 'Breakdance'
• 'Eternal Father'
• 'Kiwi Watercolours'
• 'Leopard Frog'
• 'Lunacy'
• 'Parkish Gold'

HVX Free, Mottled Hostas

A few interesting hosta varieties show the mottled pattern that is common in virus infected plants, but are in fact free of Hosta Virus X. There are a couple slight differences in the way these plants display the markings. The markings in the HVX free plants are more random and do not follow and bleed out from the veins as they do in HVX infected plants. The markings in the HVX free plants are also very dependent on light exposure. The markings can be lighter or darker depending on the amount of light the plant receives. Markings in HVX infected plants are not affected by light intensity. Hosta Virus X free, mottled plants also commonly fade to a solid color by the end of the season. If you like the mottled look, the markings on these hosta varieties are not caused by Hosta Virus X. Exactly what causes these types of markings is still unknown.

• 'Cynthia'
• 'Kiwi Forest'
• 'Laella'
• 'Wild Bill'
• 'Xanadu Paisley'

Dealing with HVX Infected Plants

Hosta Virus X infected plants will not recover, so they must be prevented from spreading the disease to healthy hostas. If you have a virus infected hosta in your garden, it should be destroyed immediately to prevent the virus from spreading to neighboring plants. Dig up the plant and send it to the landfill or burn it. Hosta Virus X can not survive in the soil, so as soon as the infected roots remaining in the garden have decomposed, you can safely plant another hosta in the same location.

The big wholesalers and growers are starting to take this problem seriously, but there are already so many infected plants out there, it is up to the home gardeners and collectors to do the rest. It is my personal feeling that these plants are like a ticking time bomb. As long as they are in the garden, they pose a threat.

Hosta Virus X and Nurseries

Retail nurseries are in an especially vulnerable situation. They often cut off bad leaves and scapes which puts them at high risk for infecting the rest of their stock. It would be a wise precaution to avoid cutting plants that came from suspected varieties and suppliers. Quarantining these plants in an isolated area for a year will allow time for symptoms to appear.

Help Spread the Word About Hosta Virus X

There is still much to learn about Hosta Virus X, but we already know enough about this virus to make a difference. With careful observation and garden management, there is no need to panic or even worse...stop buying and growing hostas!! This virus is so new there are still many gardeners, collectors, and even nurseries who have never heard of Hosta Virus X. Do your part to help educate hosta growers in your area about HVX. The following pdf document is a much condensed version of this article, but gets the main points across. Feel free to download it and print off copies for your favorite hosta friends and nurseries.

• Hosta Virus X Flier (This file may take several minutes to open. You'll need the free Adobe Acrobat Reader to view this file.)

Further Information on Hosta Virus X

• Hosta Virus X - A Clear and Present Danger - Bill Meyer tells about his first encounter with HVX and explains how threatening this virus is.
• Warning - Hosta Virus X - A brief introduction to HVX with pictures of infected hostas.
• HVX Pictures - More photos of hostas that tested positive for Hosta Virus X.
• The Striptease HVX Issue... - A forum discussion on Hosta 'Striptease' being infected with Hosta Virus X. Includes pictures.
• Hosta Virus X Epidemic - A lengthy forum discussion on the HVX epidemic. Many photos included.
• Hostas with Odd-Looking Leaves May Have A New Virus - A pdf file describing Hosta Virus X and how to prevent spreading it. Reprinted from Fine Gardening, June 2004. File courtesy of Rob Mortko. (This file may take several minutes to open. You'll need the free Adobe Acrobat Reader to view this file.)
• Differential Response of Hosta Cultivars to Infection by Hosta Virus X Potexvirus - A Basis for Practical Disease Management - Dr. Lockhart's research results on resistance to HVX of 57 different hosta varieties. (Must pay for the full article.)
• Hosta Virus X - Short briefing on HVX from the Wisconsin Pest Bulletin. (This file may take several minutes to open. You'll need the free Adobe Acrobat Reader to view this file.)
• Hosta Virus X - A new threat to one of our favorite shade perennials - Basic information and pictures of HVX. Also includes a Hosta Virus X Resistance List based on Dr. Ben Lockhart's three year trial study.
• Hosta Virus X - Basic information and pictures from the Missouri Botanical Garden.
• Virus Problem Plagues Hosta - News release about Hosta Virus X from Iowa State University. (published February 19, 2007)

I am by no means an expert about Hosta Virus X!! If you have information, links, or photos that will make this article better, please email me at info@inthecountrygardenandgifts.com.