Hosta Deseases: Hosta Virus X




As early as 1999 hosta breeders started seeing bizarre looking sports which had blotches and patches of darker leaf tissue within the typically-gold parts of leaves. Initially, these mutants were thought of as just another interesting sport. However one person, Dr. Ben Lockhart of the University of Minnesota, took the time to dig into the new phenomenon and he actually determined that the cause of these mottled leaves was a previously-unknown virus: Hosta Virus X (HVX).

While Dr. Lockhart was successful in isolating the cause of the leaf disfigurations, to this day no one is quite sure where Hosta Virus X originated.

Symptoms of Hosta Virus X

Hosta Virus X affects different hosta cultivars in different ways so it is nearly impossible to provide a description of symptoms that will match each infected plant. However there are common symptoms and clues you can look for such as blue and/or green markings in areas of a leaf that should be light-colored. These darker markings typically follow the veins of the leaves and look like they 'bleed' out into the areas between the leaf veins - like ink spreading - giving the area an overall mottled appearance.

Leaves infected with the virus are sometimes lumpy and puckered, presenting a different thickness or texture than what is considered 'normal' for the plant. On occasion, the virus presents itself by causing small, dry, brown spots, or twisted and deformed leaves. The virus is often difficult to detect on normally-dark solid colored leaves because the mottling is very subtle. However, if you hold the leaf up to the light you will find that in infected plants the veins will be lighter green and mottled.

In some cases, the virus is very obvious on dark colored plants and looks as though someone spattered a bleaching agent all over the dark leaves. And, to make things even more complicated, some hosta do not show visible symptoms of the infection at all. These plants look healthy and happy and only after a year or two will any symptoms show up that can be detected visually.

How the Virus travels from Hosta to Hosta

While it is still unknown exactly how the virus travels from host to host there are some solid theories. The most obvious is via sap from one hosta infected with Virus X being transferred to another plant. This can happen in several ways, like tools, or even your hands if you handle an infected plant, damage a leaf by mistake and then pick up another plant. If you use your imagination you can think of many ways the sap from one plant can get onto another -- rabbits, deer, insects crawling on fresh cuts and trimmed portions of a plant -- really, ANY mechanical means is a possible transfer vector.

The Virus can be transmitted during the Tissue Culturing process, however, most reputable labs screen their stock plants carefully before investing the hundreds of dollars and months involved in creating Tissue Culture plants for nursery stock before using a plant for mass tissue production. That is why the current belief is that the primary source of the Hosta Virus X epidemic is a result field-grown hostas being divided and cross contaminating large masses of 'wholesale grower' stock. This makes sense in operations where growers propagate hostas mainly by physically dividing hostas.

The theory is that several large-scale growers (in Holland, and a few in the United States) now have it in their growing fields and spread the infection during the harvesting process. During harvest, plants are dug up using the same tools so one infected plant can contaminate an entire field! Also, it is a common practice for plants to be 'power washed' to remove soil and loose leaves. Several growers in Holland re-use the rinse water so it's possible that leaves stripped away during power washing expose fresh sap which gets into the entire tank of rinse water.

To make things more frightening, a researcher just confirmed that the virus can be transmitted via hosta seeds! At this time, however, it is uncertain if the virus can be transmitted via pollen or if the seeds that tested positive for infection are infected down to the embryo inside or if the infection is just present on the surface and can be removed with sterilization.

Preventing Hosta Virus X from Spreading

The obvious but not always easy way to protect your garden is to remove infected plants immediately upon suspecting that the virus may be present. Avoid bringing home any spotted or blotchy plants from the store. Also if you find one suspicious plant at the nursary, consider all their plants infected because not all infected hostas show visible symptoms. And, even if you feel that your nursery purchases are virus free, keep them separated for a few years, just to make sure your existing babies remain safe.

STERILIZE YOUR TOOLS! When dividing or trimming your hostas always sterilize your tools. Using just bleach won't guarantee virus neutralization. So you might create yourself a 'disinfection assembly line' -- Start with foaming Lysol disinfectant, let the disinfectant do its job for the required amount of time, then follow up with rubbing alcohol, and possibly ammonia as well. Do this between plants, every time, and you can rest easier knowing you won't be jeopardizing your entire collection.

Virus X and certain Cultivars

Before anyone realized that the new funky-color-patterns was because of a virus, some of the infected plants were given cultivar names and marketed. All plants of the following varieties ARE infected with a virus:

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

On the flip side, some cultivars are mottled but are in fact not infected. This makes it terribly confusing for anyone trying to figure out if their hosta is infected! The good news is that there are a few very slight differences in mottling characteristics between infected and non-infected plants - the naturally mottled plants show a more random color pattern which does not follow the veins quite as consistently as in infected plants.

Also you'll find that normally mottled plants will be affected by light exposure - lighter or darker - depending on the amount of light the hosta gets. If you are unsure if your mottled hosta has the virus and do not want to spend money on the test kit, isolate your hosta in an area that has significantly different sun exposure - infected plants are not affected by light intensity. If your hosta changes its mottling you have an indication that you just have a weirdly-mottled plant as opposed to an infected one. Also, naturally mottled plants are more prone to fade to a solid color by the end of the season. If you take the time to watch your suspicious hostas you can see if they fit any of these characteristics to help you identify which may be candidates for infection.

The markings on the following hosta cultivars are not caused by a virus:

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

What to do with infected plants

Infected plants will NEVER recover, so it is imperative that you destroyed any plant that is infected to prevent contaminating the rest of your collection. Carefully dig the infected plant up and try to get as much of the root material as possible. You can either dispose of it by burning it, or sending it the landfill with the rest of your household refuse. The virus can not survive in the soil so if you wait till any remaining organic matter from your infected plant completely decomposes and there is no fresh sap anywhere, you can safely plant another hosta in the same spot.

Conclusion

While this virus is still a 'relative-unknown' we do know enough to protect our own gardens. The key here will be awareness. There are still many nurseries who have never heard of Hosta Virus X (or HVX) so you can help educate them. The nice folks at inthecountrygardenandgifts.com have provided this handy PDF document you can download and print it to hand out to anyone who you think would benefit:

Hosta Virus X Flier (You'll need the free Adobe Acrobat Reader to view this file.)

More Information about Hosta Virus X (HVX)

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