Hosta FAQs: What can go wrong? Hosta viruses...

Dew you know

what to dew?

'Sum and Substance' with virus. Notice the "melted plastic" look of sunken tissue, and uneven discoloration (of what should be a chartreuse hosta).

'Seventh Heaven' is a streaked hosta.

'Revolution' is a speckled hosta.

'Undulata' gets "summer uglies," which are not virus.

'Gypsy Rose' with late-season mottling: suspicious but not virused.

While there are lots of places online to find information about hostas (see our links), and of course a number of books you can buy for ready references, we didn't feel that there was a good place online for FAQs (Frequently Asked Questions), as experience with the American Hosta Society's Facebook page has shown. We hope you find this useful. The good stuff is at Part I. Here are FAQs on Hosta Virus X, the most serious problem of hosta commerce.

Use the little ˅ to open (and then collapse) each answer. Be sure to scroll to the bottom for instructions on keeping your garden tools clean.

What is the Hosta Virus?

I’ll leave this answer to an expert on the subject, Chris Wilson of Hallson Garden Perennials in Michigan. Hosta Virus X, a potexvirus identified by researchers in 1996, has developed into a major problem, and is probably the number one threat to hosta collections around the world. It will cause strange mottling, spotting, and even distortion on hosta leaves. It will never kill the plant, but it may struggle to grow and will look worse and worse as it becomes more infected. Thousands upon thousands of infected plants have been distributed by major wholesale hosta suppliers into the US. The primary mode of transmission of the virus is through damaged roots, but any wound (in roots or leaf) can transfer infected sap to a wound on another plant. When an infected plant is cut with a knife, pruners or shovel the virus may be carried in the sap and then transmitted when the tools are used to cut into a healthy plant. Additionally, the virus is transmitted when washing and handling, such as preparing plants for shipping or planting. In Holland roots are cleaned with pressure washers where the water is used over and over again, and it is speculated that is the source of the major infection coming out of Holland. The act of handling and wounding multiple plants can lead to infection that doesn't show up for several years as the point of infection was so recent [just before shipment, which means the batches would pass the spot-testing inspection on arrival in the U.S.].

Is there a cure?

No. The virus is within the cells and cannot be killed without destroying the whole plant, which is certainly not a cure.

What does HVX infection look like?

There's a multi-page album of infected hostas at the Hosta Library. Warning: graphic images. In general the virus will cause dark splotches like a spreading ink spot from the veins of the leaf. In dark hostas an infected hosta may not show discoloration, but the virus will cause collapsed tissue looking like melted plastic. In time the hosta will be almost unrecognizable. Shown at left is a heavily infected 'Sum and Substance'. Compare this to the streaked and speckled pics below. Note that a virused leaf will not really change its presentation of the virus as the season goes on, where other changes in leaf color can happen during the season.

Can any hosta get HVX?

Yes. Symptoms may be very difficult to spot on Sieboldiana-type hostas like 'Elegans', but all can be infected. Previous statements that such hostas were “immune” have since been disproven, although they may be considered “resistant.” Note also that effective transfer of the virus from infected to healthy plant is greatly reduced once the plants have flowered, i.e., later in the season when the sap flows less freely. This may be why the early-blooming Sieboldiana types seemed immune. On the other hand, some hostas may seem especially prone to HVX infection ('Striptease' and 'Sum and Substance', for examples), but this is more related to the way in which they were mass-produced for the garden market.

How long does it take for HVX to show up?

Some hostas were known to show infection in a short time, even the next year. Other hostas (notably 'Sum and Substance') may harbor the virus (and be infective to others) for periods of five years or more before showing obvious signs. Still other hostas (like 'Elegans', mentioned above) may show only minor symptoms years after infection.

Are there other viruses that affect hostas?

Yes, unfortunately, although HVX is the most common. Tobacco Rattle Virus, Tobacco/Tomato Ringspot Virus, and Impatiens Necrotic Spot Virus are known, and there may be others. (Rare instances of viruses that DO cross into other plants.) There are also some fungal and bacterial diseases that affect hosta, but these are rarely serious. Fungal infections can be treated with a fungicide, and bacterial infections my yield to a product like Bayer Three-in-One Rose Care or a barrier protection like Phyton spray.

I think my hosta is infected. What should I do?

Often it’s quite obvious, once you have seen other pictures of infected plants, that your hosta is indeed infected. If so, follow the disposal guidelines below. If you’re not sure, you can first visit the Hosta Diseases and Pests group on Facebook, post a picture of suspect leaves, and ask for opinions. Even then the opinion may be that you should have it tested. The tests come from Agdia, and yes, they are not cheap. If you’re worried about contaminating your entire collection, though, it can certainly be worth it. Or you may simply decide to destroy any questionable plant, or (at least) wait a year while keeping the plant in strict quarantine. If you discover that you have a plant infected with Hosta Virus X then the plant should be dug up and sent to the landfill or burned. If you are careful to quarantine the plant (always cleaning tools as described below), you can wait until late in the season to remove it, as there is less flow of infected sap at this time. Dig the entire plant getting as much of the roots as possible. Do not put another hosta in the same hole for at least two seasons, as the root residue has been shown to be infective for at least that long; most careful gardeners would put a fern, astilbe or a rock there instead. Note that you cannot successfully decontaminate the hole where the hosta was (using bleach, boiling water, etc.).

I saw an infected plant in a nursery or in another garden. What should I do?

Please inform the owner. A nursery is generally licensed by the state department of agriculture, and they are required to provide disease-free plants. They should be made aware that if one plant from a supplier (at least of a single cultivar) is infected, then the whole batch should be considered infected. If they resist, take a picture of the plant and tell them you will share it with the state department of agriculture. If you see an infected hosta in a private garden, gently point the owner to appropriate information here or elsewhere. If the pushback is that they think it’s “interesting,” challenge them that it will infect, and affect, every hosta in their garden until everything looks sick. How interesting would that be? And certainly don’t share any plants with them!

Is there a test?

Yes, Agdia, a leading provider of plant pathogen diagnostics, provides an easy-to-use ImmunoStrip test system for Hosta Virus X. They are not inexpensive: currently a pack of 5 tests is $50, or 25 for $125. You take a quarter-sized piece from a suspect leaf, mash it up in the buffer solution-filled bag, insert the test strip, and read the result in about 30 minutes. Detailed instructions are provided with the kit, or can be downloaded from the website. Unused test kits should be stored in the refrigerator, and are good for at least a year. The test is very accurate when the amount of virus in the hosta reaches the threshhold level, which can be before symptoms are visible. Newly infected hostas, with low but increasing levels of virus, will likely give a negative result, which explains how imported infected hostas can slip through the testing procedures required by the USDA. (Even then, some percentage of imported infected hostas is permissible!) Note that this test does NOT diagnose other viruses (see Q below).

Can anything other than hostas get HVX?

Not as far as we know. In general, viruses are very specifc to their hosts, and only rarely mutate to affect (or infect) another host. So while it might be possible for HVX to infect a very close genetic relative like Agave, this has not yet been known to happen.

How do I clean my tools to keep from spreading viruses?

Here’s a long and thorough answer from Chris Wilson:

Shovels: When digging up hostas, especially older/larger ones, you invariably cut into the roots. If your hostas are growing in close proximity to each other there is also the real possibility that when you dig up one plant you are cutting right through the roots of a neighboring plant. If one plant is infected and in the process of digging it you cut through a healthy plant's roots you could very quickly and easily spread the virus to the healthy plant.


So to prevent this sap transfer when digging out infected plants we suggest:

1) Dig from the side that is farthest away from any other plants, 2) Dig closer to the crown of the infected plant, and/or 3) Consider digging with a spading fork instead. These have a reduced surface area and instead of cutting out plants they pry out plants, therefore reducing the amount of cut, root to root contact as compared to shovels.

When you are done digging a known infected plant you will definitely need to thoroughly clean off your digging tools. You must remove as much of the plant sap as possible, which means scrubbing and wiping off the surface of the shovel or spading forks, preferably with disposable rags or towels. You may also want to disinfect the tools to further reduce the chance of virus remaining, especially if you were digging and cutting into a highly infected plant.

Cleaning can be done with just about any household cleaner, with the focus on removing the dirt and plant sap. If the plant sap is removed, so should the virus. Disinfecting can be done by soaking in bleach or Lysol (or other known virucidal cleaners), although it is still important that you remove the dirt and sap before soaking. Most of the known, tough to kill viruses are neutralized after a 10 minute soaking in a bleach (1 to 2%)** or Lysol solution, and although we aren't certain how long it takes to kill HVX this is probably a safe estimate, especially if you've taken steps to remove all the sap.

Again, if working with a known infected plant I recommend you thoroughly clean off the dirt and plant sap and also soak in a disinfecting solution. For everyday use it is generally accepted that if you surface clean your tools this will neutralize and eliminate most of the plant sap, and without the sap this will greatly reduce the chances of spreading the virus.

NOTE: Simply dipping your shovel or pruners in a cleaning solution for a brief moment will not provide any protection from the virus. HVX is a highly stable virus so you must work to remove and neutralize the plant sap first, then soak to disinfect.

** When mixing bleach you want a 1 to 2% solution to kill viruses. Most bleach is sold in a 3% solution, so you would mix one cup of bleach with one cup of water for a 1.5% solution. "Ultra" bleach is usually a 6% solution, so you would mix one cup of ultra bleach with three cups of water for 1.25%. When cleaning with bleach this can rust metal, so some people like to oil their tools afterwards to prevent rust. The bleach chemical also evaporates quickly from a bucket, so mix a new solution very often or put a lid over the bucket when not in use to prevent it from evaporating too quickly.

Pruners and scissors: When cutting into hosta leaves and scapes there is a large amount of plant sap transferred to these tools. Even moreso than when digging, although digging into neighboring roots transfers the virus quite easily too. Cleaning your pruners or scissors between cuts must be even more thorough than cleaning shovels.

For this job one of the easiest ways to clean is using disinfecting wipes. Clorox wipes can be used to both remove the plant sap and provide some surface disinfection.

Another method is to use a spray bottle of rubbing alcohol or Lysol and lots of paper towels. We purchase 90% rubbing alcohol and put that in a spray bottle for everyday scissor and pruner cleaning, but we also mix up a spray bottle using Lysol concentrate mixed at a very high rate and use that when working with known or possibly infected plants when we sample leaves for testing. Spray the tools down thoroughly and then wipe them off with paper towels. Soak another paper towel and cut through it with the tool to remove sap from the blades and hard to reach areas. Then soak one pair of scissors or pruners in one of these solutions while you use a second one to make the next cut.

If there is a possibility of having infected plants in your garden you may also want to avoid cutting any leaves and scapes for a while so you can keep a close eye out for possible symptoms.

Knives: Knives are often used to divide plants. Use a sharp knife to prevent getting sap into serrated edges, making them a lot easier to clean. Again, use rubbing alcohol, disinfecting wipes, or Lysol, and lots of paper towels to make sure you are cleaning thoroughly between plants. [One clever gardener relates that she purchased a dozen inexpensive steak knives at a dollar store, then uses one for each plant, tossing the used knife into a “dirty” bucket. When all the knives are dirty, she washes the whole set.]

Hands: When working with hostas don't forget to wash your hands. Washing with soap and water will help, especially when working between batches of plants such as in a nursery, then wipe with disinfecting wipes. Disposable latex gloves are also handy, just make sure you change them or wash them between batches and between divisions when dividing multiple plants.

Final notes: HVX is only spread when plants are damaged and plant sap is released. You have to cut or break an infected plant, get sap on your tools or hands, then break or cut a healthy plant and transfer the sap to through the cut. Just touching plants will not infect them but because we do so much pinching, pruning, and dividing of hostas it is very important to clean methodically between plants. While there is some suspicion that the virus could be spread by bugs or even by the mouths of deer or rabbits, this seems unlikely, although any time there is close contact between wounded plants there is the possibility of sap transfer.

Thanks, Chris!


If you want to read some happy stuff now, consider the FAQ Part III on starting new hostas from seed!

Lemme see Part III!

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