Seeing Spots — Hosta Virus X
(Editor's Note: This article was originally published on June 9, 2008. Your comments are welcome, but please be aware that authors of previously published articles may not be able to respond to your questions.)
I am by no means an expert on hosta. Like most gardeners, I have sunny and shady areas to my property where I happily plant hosta varieties. Each year I treat myself and my hosta-loving husband to a new hosta or two. Additionally I often solicit interesting plants from friends and family who have some to spare. I even picked up two hosta at this year’s Dave’s Garden Iowa Roundup. In all, I have 13 varieties growing at my house. Soon I’m sure we’ll run out of shady spots and painfully look for spots to put newly developed varieties on the market. So you can see… I am clearly not an expert, nor even a knowledgeable hosta gardener. I don’t worry about slugs or foliar nematodes or think about identifying new sports. I simply love the way they look, love that they are care-free and love the purpose they fill in our shady spots.
With my new hosta planted this spring, all was joyous in my “Happy Hosta World.” And then it happened… along came the Hosta Virus X scare to send me into a tailspin of worry.
Recently while attempting to identify some hosta from trade on the Dave’s Garden Hosta Forum, I ran across a thread on Hosta Virus X (HVX). “Hosta-whozitz-whatzitz?” I curiously clicked on the post and began to read something that could jeopardize my easygoing relationship with Hosta. Now even pesky slugs seem tame in comparison to HVX. But after much reading I’m not nearly as panicked. This virus is a certainly a threat to residential hosta collections (the virus currently does not infect other perennials). The good news is that understanding HVX and careful plant hygiene can keep the virus from spreading further.
HVX is a virus infecting hosta plants across the globe. Investigators report that it is currently widespread globally. The virus shows itself in the leaves as a subtle mottling, spotting or blotching or thin, puckering tissue. The virus was first identified in 1996 at the University of Minnesota by Dr. Ben Lockhart who still studies HVX at his UM Pathology Department. It has been present in plants for many years before identification, however. In fact, several hosta sports were named as new cultivars only to later discover that they were only plants disfigured by the virus (see bottom of this article). The virus does not kill the plant but sadly there is no cure.
What it Looks Like
|Inkbleed — An early symptom, Inkbleed is a discoloration of the leaf, often along the veins of the plant.||Cell collapse — As the virus progresses, signs of tissue collapse emerge. Areas affected will look more dull and thin, as if part of the leaf was scraped off. Surrounding healthy tissue often looks puckered as a result.||Mottling — This symptom is a blotching/spotting which indicates HVX. However, this symptom also is indicative of other hosta viruses. |
How it Spreads
HVX is type of virus (potexvirus) that spreads mechanically through the sap of the hosta plant. Although studies have shown that an infected parent plant can produce 10% infected seeds, the majority of infection is still sap related. For example, say you were admiring the beautiful scapes (blooms) in your collection. You decided to collect some leaves and scapes for an indoor bouquet. You got your garden scissors out and cut leaves and plants from each of your five or so favorite plants. What you didn’t know is that the second plant you cut carried HVX. The sap from that plant was still on your scissors and then mixed with the sap from plants three through five, infecting them. You didn’t even KNOW that plant number two was infected. Unfortunately, the really evil thing about this virus (in my opinion) is that it can live in the plant for years before showing symptoms.
Think about how many times you pinched a leaf that had slug or hail damage and then moved on to the next plant. How many splits of this hosta have you provide to your gardening friends? What about the time that you (oops!) ran the mower over the edge of a whole row of hosta?
Scary, right? Right.
The nightmare continues at larger growers who do not practice sanitary procedures. Imagine rows of hosta growing in a field. When it’s time to weed, a mechanical apparatus moves down the rows, perhaps slicing roots of the hosta plants along the way. If HVX was present, it has now been spread in a very large way.
What Is Being Done
Take a deep breath… help is on the way.
Research — The American Hosta Society (AHS) is presently in the midst of the Hosta virus X research project. The two-year project with the University of Minnesota intends “to clarify methods of transmission and understand the dynamics of Hosta Virus X spread, so that we may protect our plants and gardens.” 
By researching the virus, AHS hopes to answer common gardener questions such as “How long does the virus stay on infected tools and how can they be disinfected; how long does the virus stay in the soil, etc.” AHS posts project updates on their website.
Education — In addition to AHS, there are some major players in educating consumers about the HVX threat. Hosta Library generously offers many of the pictures in this article for use in educating the public. Hallson Gardens, a leader in the fight against HVX, offers a hosta virus X discussion forum where gardeners may post pictures of their suspect hosta and discuss the virus. Many garden centers publish information on their websites, while garden publications report on the matter too.
Testing and Guarantees — There are two tests to screen for HVX. The first is ELISA (Enzyme-Linked Immunosorbent Assay) the most common screening test in the lab. The second test — ideal for on-site use — is the ImmunoStrip® from Agdia. Representatives from Agdia report that it has a greater than 99% correlation with ELISA. 
Many members of American Hosta Grower's Association report confidence in their stock due to diligent screening. Mike Butler of Bloomin Designs says “Today, we only buy-in hostas from reliable sources that provide a 100% virus-free guarantee, which often requires relying on tissue-cultured liners.” Sylvia from Hostas by Sissinghurst adds, “My first question to any grower I deal with is their awareness of HVX…” In his Fall 2007 update, Bill Meyer of Hosta Library has some good news and bad news. The good news, “Despite the seriousness of the HVX epidemic, I'm happy to report that your chances of getting HVX-infected hostas from hosta specialty nurseries these days is virtually nil.”  However, the threat of obtaining infected plants from other retailers still remains high. Hostas sold at rock-bottom prices often come from overseas growers with less stringent screening methods. The Netherlands Inspection Service for Horticulture conducts ELISA tests for growers who voluntarily submit samples.
Most of the Dutch growers however, perform visual plant inspections rather than full testing. Plants showing visual signs of infection are distroyed but others in the same batch that pass visual inspection are allowed to be sold. Chris Wilson from Hallson Gardens indicates that last year he purchased “guaranteed HVX free” hostas from a Dutch grower. One out of four batches turned out to be badly infected. Combined with other purchases from Dutch growers, his HVX-infected batches totaled eight of 14. Stories like Chris’s are quite common from other U.S. retailers and wholesalers regarding Holland imports.
What You Can Do Now
Clean your tools — Good plant hygiene goes a long way in keeping HVX out of your garden. Leave your hosta leaves on the plant and don’t cut the scapes. If you must cut or divide the plant, sanitize your tools after use. In her Fine Gardening article, Bonnie Blanchette suggests using a 10% bleach solution on tools after working on each plant. For more in-depth information on proper tool cleaning as well as digging an infected plant, Chris Wilson of Hallson Gardens offers a helpful thread on the Hallson Forum.
Test your plants — If you suspect you have an infected plant or you just want peace-of-mind, get your hosta tested. University labs offer testing at various prices. If you prefer, order test strips from Agdia (links found a the end of this article). If the plant shows symptoms of the virus, take a picture and post it on the Dave’s Garden Hosta Forum, or at the Hallson Gardens forum.
Throw out infected plants — Remove any infected plants and let them dry out and die, then straight to the garbage. Disinfect your tools and hands before working with any other hosta. Wait a few weeks until any leftover roots in the soil have dried up and died before you replant a hosta in the same location.
Buy from reputable sources — If possible, only buy from specialty hosta growers or at least a high-end nursery. Don’t be afraid to ask them about their knowledge of HVX. Are they knowledgeable and aware of the virus or are their answers vague and uncertain? Buy from big-box retailers at your own risk! While discount prices might be attractive, think of how much money you might spend replacing your entire collection.
Avoid trades — You might consider halting hosta trading until a later date. If you know your “tradee,” discuss the HVX threat before you proceed. Talk over details such as how long you or they have had the plant, what kind of plant hygiene you practice, etc.
Monitor your plants — Keep an eye on your hosta plants even if you have had them for a few years. Monitoring them in this fashion will help you look for other symptoms of disease such as foliar nematodes. Tony Avent from Plant Delights Nursery reminds us, “Foliar nematodes on hosta are a far worse problem than [the] virus will ever be.” One reason to fear foliar nematodes is that the parasites can spread to other hosta within a six-foot range of an infected plant. With an infected HVX hosta, two plants can grow side by side and not be subject to the other’s HVX. In fact, if you have a nematode-infested plant, AHS recommends that you destroy not only that plant, but all hosta in a three- to four-foot radius. I guess I’d rather be destroying one HVX plant than so many others near a nematode infestation.
Spread the word and stay informed — If you see infected plants at any nursery — big-box or high-end — notify the manager and inform your gardening friends. Ignorance and apathy enable the spread of the virus. If you are met with skepticism or disdain from retailers, take comfort that at least YOU are a proactive part of the solution. Check in with the Hosta Library and AHS for updates. Scientific research is constantly updated. Hosta Library reports, “…research in Korea by Ryu KH, Park MH, and Lee JS has discovered that HVX can be transmitted through seed of infected plants and that there is more than one strain of the virus.” This disturbing discovery clearly indicates more research is in order.
There has been some chatter on the Internet about “immune plants,” but Hosta Library lists this as a myth. Early studies showed some hosta were more difficult to infect than others. Since that time, some of the “immune” varieties have become infected.  Keep reading Dave's Garden and other hosta forums for updated information and research developments.
Doing my “homework” for this article indeed opened my eyes to the HVX threat. What I learned convinced me of one thing: DON’T PANIC. Devise an HVX plan — mine is in place: practice good plant hygiene, purchase from reputable sources and monitor existing plants. I purchased all my new plants this year from high-end garden centers. Though not specialty retailers, I’m optimistic that their stock is clean.
Adding new hosta to my collection was a huge joy for me this year. In fact, I probably went a bit overboard. The front of my house is finally greening up. I transplanted my favorite, ‘June’ from a temporary spot where I placed it over four years ago after moving to this house. I added ‘Great Expectations’, ‘Independence’ and 'Lakeside Shoremaster' to the front beds. In the back I tucked away two hosta obtained from the Iowa Roundup and one from my Grandmother’s house. I still have four more plants to move from my temporary “nursery.” 2008 is a good hosta year for me. And you know what? I’m no longer afraid of HVX!
 Hosta Library
 Hosta Library
 Hosta Library
More Reading and Resources
“Transmission of Hosta Virus X (HVX) Under Normal Conditions of Hosta Cultivation and Commercial Production”
“Hosta Virus X — A Brief History of the Epidemic” Chris Wilson, Hallson Gardens
(A few are listed here, contact your local extension office to see if testing is available.)
Varieties named for viral infections (including HVX):'Blue Freckles' (probable HVX)
'Breakdance' (confirmed HVX)
'Dotted Fantasy' (probable HVX)
'Eternal Father' (confirmed HVX)
'Kiwi Dreadlocks' (probable HVX)
'Kiwi Watercolours' (probable HVX)
'Leopard Frog' (confirmed HVX)
'Lunacy' (confirmed virus)
'Pamela Ann' (probable HVX)
'Parkish Gold' (probable HVX)
'Strip Show' (probable HVX)
'Tye Dye' (probable HVX)