Hosta Virus X: the disease and containing its spread

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By Phil Reilly,
Reillyís Country Gardens Nursery,
Ottawa, Ontario, Canada.
December 30, 2006

The following article, in an edited form, was published in the Ottawa Horticultural Society's Newsletter, OHS News, in January 2007.

Introduction

The September 2006 issue of OHS News (The Ottawa Horticultural Society's Newsletter) presented an important article (Hosta Growers Beware) alerting OHS members to the existence of a poorly known hosta virus inoccuously called Hosta Virus X (HVX).

OHSís concluding recommendation (i.e. ìAll hosta purchases carry the ëcaveat emptorí warning. Ask about the source before you buy.î) prompted me, as a nursery operator, to further investigate available info on HVX and what the recommendation might mean to nurseries.

HVX should be considered a major problem in the hosta world. Hostas are one of the most commonly purchased ornamental garden plants as they have a reputation for being relatively pest and problem free, showy, and able to be grown under many light and soil conditions as long as uniform soil moisture is provided. As the word spreads about being cautious about hosta purchases, there is likely to be financial repercussions to those in the nursery industry.

The objective of ridding the world of HVX is correct and, within the nursery and garden center world, steps are being taken to make sure that any hosta growers and vendors not familiar with the disease will soon have the most up-to-date information on its identification and understand how to minimize its spread.

The President of the Perennial Plant Association (PPA) informs me (personal communication Dec. 11/06) that a HVX seminar session is planned for their 2007 Symposium in Columbus, Ohio. An expert panel drawn from the virolgy, plant propagation and nursery spheres will provide the horticultural world (propably about 1000 attendees including many garden writers) with everything needed to know about the significance, mechanisms of spread, and virus containment and control options.

To make sure everyone working for our nursery is informed about HVX identification and control strategies, I have obtained a 26-minute HVX-CD from Michigan's Hallson Gardens (they are a leader in alerting the hosta world on the HVX issue). This CD is also available to be shown to garden clubs.

What are Hosta Virus X symptoms? (The following synopsis of HVX information comes from a variety of web sources.)

Symptoms appear on leaves as line patterns (especially along veins), mosaic patterns, blotches, puckering, twisting, or ringspots. However, certain cultivars may express only small necrotic (brown/dead) spots. Symptoms vary by cultivar and time of infection. Some hosta cultivars have natural coloring or striping, so it is important to know what is ìnormalî for a given cultivar before becoming alarmed about the presence of HVX.

There are few photographs of the range of symptoms of HVX in the plethora of conditions under which hostas grow. Photos of some HVX-infected plants can be seen by clicking on the following links:

a) Viruses on Hostas: photos of HVX from Dr. Ben Lockart and Walters Gardens

b) Photos from Hostalibrary.org

c) Photos from Michigan State Universityís Landscape Alert publication series

d) Fine Gardening magazine article, May/June 2004 - Hostas with Odd-Looking Leaves May Have a New Virus: The best protection against HVX is to buy healthy plants

The Ottawa Horticultural Society, under Jeff Blackaderís guidance, is in the process of searching for photographs to place on a new page of their web site. By the start of the 2006 gardening season look for a gallery of photos showing HVX symptoms in a wide range of hosta cultivars. Jeff welcomes volunteers to help him with the web pages and certainly welcomes any photographs of, or additional links to, infected hostas.

What hostas are suspect of carrying HVX ?

All plants with the following cultivar names have been demonstrated by labortary testing to be infected (Infected Cultivars in the Marketplace/hostalibrary.org). These hostas are not new cultivars, they are just heavily-symptomatic infected plants:

"Breakdance", "Eternal Father", "Kiwi Watercolours", "Leopard Frog", "Lunacy", "Parkish Gold".

Phil's opinion: It is prudent to get rid of any of the above known infected varieties/cultivars from gardens and from distribution through traditional vendors, plant exchanges and friendly trade amongst gardeners. Existing plants of the above six cultivars should be sent to landfills.

The following hostas have a probable genetic background to HVX (Infected Cultivars in the Marketplace/hostalibrary.org):

'Blue Freckles', 'Dotted Fantasy', 'Kiwi Dreadlocks', 'Pamela Ann', 'Strip Show' and 'Tye Dye' .
Phil's opinion: Until it can be shown that these hostas are virus-free, there are no positive reasons for having them either in gardens or in circulation in the retail trade.

The following hostas have been reported to have some infected batches in the marketplace (Infected Cultivars in the Marketplace/hostalibrary.org):

'Color Glory', 'Fan Dance', 'Golden Prayers', 'Harvest Glow', 'Hydon Sunset', 'Kara', 'Little Aurora', 'Louisa', 'Montana Chirifu', 'Abby', 'Diamond Tiara', 'El Nino', 'Ground Master', 'Guacamole', 'Janet', 'June', 'Katherine Lewis', 'Krossa Regal' (+ 2nd virus), 'Minuteman', 'Moonlight Sport', 'Night Before Christmas', 'Opipara', 'Pacific Blue Edger', 'Paradise Joyce', 'Patriot', 'Queen Josephine', 'Regal Splendor' (+ 2nd virus), 'Revolution', 'Richland Gold', 'Rim Rock', 'Sagae', 'Sugar and Cream', 'Sun Power', tardiva (sp.), 'Wide Brim', and 'Yellow Splash Rim'.

For these hostas, look for symptoms in plants in your gardens and plants in the trade. Discard hostas with HVX symptoms, donít buy any of these which have symptoms and advise sellers of these plants with HVX symptoms of your observations.

It may be hard to determine which hostas are infected.

At the home garden level (indeed throughout the hosta industry,) learning to identify HVX symptoms is an important tactic in controlling the local spread of this hosta virus. Hosta Virus X is not the only virus known to occur in hostas. There have been seven viruses identified, by Dr. Ben Lockhart of the University of Minnesota who is the leading researcher on viruses in hostas and first to isolate Hosta Virus X. (Click here for his report Occurrence of Arabis mosaic virus in Hostas in the United States.)

The detection of HVX symtoms is complicated by the variable appearance of visual symptoms ñ some individuals appear to be suscepible to the virus; others appear to have immunity to it, some individuals of susceptible varieties/cultivars exhibit symptoms; others donít, some infected plants show symptoms quickly; others take a few years to exhibit symptoms, some infected hostas die from the disease (through diminshed health); others withstand the infection.

Hostas obtained since the mid 1990ís (when the virus was first being detected in Minnesota) may have been HVX-infected whether they were purchased or traded. Hostas purchased within the last six years have the highest probability of carrying the virus with those being purchased since 2002 needing the closest scrutiny. Gardeners should become better able to identify HVX symptoms and then avoid purchasing or trading hostas having a high likelihood of being HVX-infected (see listings above).

Dispose of HVX-infected plants - There is no cure for HVX

Getting rid of known HVX infected stock is the best means of preventing the spread of the virus. The virus needs a living tissue in which to survive and it does not survive in the soil without living hosta tissue to nurture it. Remove HVX-infected hostas from the garden. Sending the entire plant, including soil ball containing the majority of roots, to a municipal waste treatment facility is a good option. Alternatively you can put the plant and soil ball in full sunshine for a couple of weeks for the sun to dry out and sterilize the plant and root system. If you wish to replant a hosta in the same location, wait a few weeks to allow any root remnants from the removed hosta to decompose. Remember, the virus can only survive if there is living tissue and sap to nourish it- once these are gone the virus soon succumbs.

Banishing HVX-infected hostas from your property reduces possible virus transferral from plant to plant by physical means such as on gardening tools or your hands. When deadheading hosta blooms or dividing hostas, with HVX spread prevention in mind, practice disinfecting your tools and hands with rubbing alcohol, methyl alcohol or a 10% bleach solution before moving on to the next plant.

Containing the spread of HVX prevents virus mutations leading to further problems

In the realm of the possible, HVX may be able to mutate to become, over time, capable of infecting other members (not just hostas) of the plant world. This alone is a good reason to get on the HVX detection, prevention, and elimination wagon.

A cloudy area is the likelihood of transmission of HVX to uninfected hostas or other plants or other species in a garden setting. Bill Meyer writes (click here for Hosta Virus X - Spring 2006 Update on the American Hosta Society web site):

ìAlthough specific research has not been completed yet on how it is spread, there is good reason to assume that it cannot be spread by insects, fungi, nematodes, or pollen. Limited research has indicated it may infect plants other than hostas, but it has not been observed in other plants at this time. Transmission through seed is not considered very likely, but not ruled out. The primary method of infecting plants is moving fresh sap from one plant to another. There are any number of ways to do this, including the cutting of rhizomes, leaves, or scapes, lawn mowers and string trimmers, handling hail-damaged plants, keeping plants with fresh cuts in contact with each other, and possibly animals feeding on leavesÖ.î

If your garden is in close proximity to another garden in which HVX-infected hostas have been recently planted, gardeners should not consider their current hosta collection to be (or will forever remain) HVX-free. It has not been ruled out that viable Hosta Virus X can be transferred in saliva of mammalian hosta munchers or injected by insect piercing/sucking mechanisms as they move from infected plants to previously virus-free plants.

Unintentional transfer of HVX- infected sap can occur in the garden at times of accidental injury by tools used in tending the plants or in dividing uninfected hostas after using the same tools which have been in contact with infected hostas. Hallson Gardensí web forum on ìSpreadability of HVXî has excellent information on this subject (click here to go to the relevant article).

Reillyís Country Gardens HVX position and advice.

As gardeners, Carole & I are like all gardeners: we want healthy plants in our gardens. As nursery operators, we acknowledge our role in providing healthy plants to our customers.

At the nursery weíll certainly be watching for and discarding any hostas in our stock or gardens showing HVX symptoms. We have not knowingly sold, nor do we have in our gardens, known HVX-infected hosta cultivars (see below for a listing of HVX cultivars). We are currently reviewing the status of about 100 pots of hostas which fall in the category of ìsome batches of these hostas have exhibited HVXî (see listing below). Weíll be questioning our suppliers about the source of these and subsequent shipments of all hostas ñ weíll be requesting only HVX-free hostas be shipped to us.

The lead paragraph of this article indicated I would address the OHSís recommendation: ìAll hosta purchases carry the ëcaveat emptorí warning. Ask about the source before you buy.î

Unfortunately the implication of this statement and advice is that a vendor is guilty of selling unhealthy stock if its source is not known.

In our case it is difficult to track the ultimate source of our plants over time and through their journey along the supply chain. We purchase plants from a number of suppliers who donít necessarily get their stock from the same suppliers year after year. We often carry over hostas from year to year (they overwinter well in their pots) , divide them when they outgrow their original pots, and then re-label them with our own labels. The source of and year of purchase of any given potted plant in our inventory may be hard to specify.

At our nursery, dodging the source question is not an indication of questionable plant health ñ it is sometimes strictly a fact. Without undertaking an expensive laboratory fee (approx. $50) for analyzing each plantís HVX-infection status, we are unable to unconditionally say any given hosta is HVX-free. To the best of our knowledge, with information available from our suppliers, we have HVX-free hostas and weíll be vigilant in maintaining this state.

Are our potted hostas always in top ëshowí conditions on the benches or in our gardens? Unfortunately not and for a number of reasons ñ mainly dealing with daily weather stresses such as heat, wind or water. Some of these visible conditions (such as brown leaf margins and brown spots in variegated tissues later in the season) may appear to be virus symptoms, but they are usually indicating either not enough or too much water in their root environments.

We agree with the OHSís ìall hosta purchases carry the ëcaveat emptorí warningî and suggest that all plants be treated with the same scepticism. Independent nurseries usually have the best track record of providing and maintaining healthy plants ñ their long-term livelihood, in the face of lower prices at box stores, depends on their ability to provide superior plants and plant knowledge.

In the nursery and garden center world, if one hosta cultivar in a vendorís inventory shows HVX symptoms, it is prudent to assume all hostas of that cultivar also have the virus. Some HVX information on the web and elsewhere suggests adjacent hostas of different cultivars to symptomatic ones should also be suspect of carrying the virus ñ especially if they are from the same supplier. However, as Bill Meyer and Cris Wilson of Hallson Gardens (previously quoted above) say on web sites, HVX transmission by insects or pruning of leaves and flower scapes is unlikely once the plants are at a retail establishment.

If you suspect hostas with HVX symtoms are being sold at a retail outlet or traded elsewhere, do inform the business or organization (make sure owners/managers/organizers get the message) that their hosta stock may contain HVX. Indicate your knowledge of the problem and enlist their help in becoming part of the solution of preventing further spread of HVX. Nurseries/retailers should be able to obtain a refund from their supplier for HVX-infected plants shipped to them.

In the world of garden clubs and fund-raising events, hostas obtained by digging and division from home gardens should be rejected from garden club/fund-raising events unless there is a 100% certainty they are coming from a garden free of Hosta Virus X. Since this certainty is hard to determine for professionals and requires laboratory testing, it is unlikely that home gardeners can profess with certainty that their hostas are virus-free.

Contact Information

Reilly's Country Gardens,
3328 Diamondview Road,
Kinburn, Ontario, Canada.
K0A 2H0

Phone: (613) 832-2965
Email: reilly@magma.ca