Articles

Hosta Virus X �
A Clear and Present Danger
Bill Meyer
American Hosta Society Education Chair

My experience with this new problem dates back to
2001 when I was visiting a wholesale nursery. I noticed
some plants with unusual markings in a batch of �Sum and
Substance�. They had green mottling and looked
interesting to me, so I started to pick one up. But as I did I
saw that several looked like it. My first impulse was to
see which had the best markings, but I realized pretty
quickly that something was wrong.
Sports are genuinely rare occurrences. They don�t
just appear in large numbers like I was seeing here. In the
batch of 100 or so plants, at least 20 had these unusual
markings. It dawned on me that I was looking at some
kind of new infection I hadn�t seen before. When I
noticed that a large block of �Fragrant Bouquet� at the
same nursery had similar markings, I began to get
concerned.
I�ve seen apparent viral infections before in some
hostas, but they were always isolated to single, individual
plants. Some of these have attained cultivar status with
names many of us are familiar with. Plants like �Lunacy�,
�Eternal Father� and �Leopard Frog� have tested positive
for viruses, but this has not really diminished their appeal.
Some nurseries have propagated these and have even
tried to deliberately infect other plants with the virus. They
were unable to do this, so many thought that these plants
were safe to grow in gardens. Some viruses are in fact
very difficult to transmit, requiring very specific means to
move from one plant to another. Unfortunately, though,
there are also viruses that can spread quite easily.
The general thinking about viruses in hostas has been
that they were never really a very serious threat. Plants
once thought to have viruses like �Sea Sprite� turned out
not to have them after all � and we�ve grown somewhat
complacent. Occasionally nurseries would see an unusual
case of a particular virus and destroy the plants, but most
discussions in recent years about hosta health problems
centered on foliar nematodes and Southern stem blight.
Although it is a little frightening to think that there are no
cures for most plant viruses and that the plants that are
infected must be destroyed, we weren�t all that worried
about it. None of them seemed to spread much, if at all.
The disease I saw in those plants in 2001 has been
identified by hosta virus expert Dr. Ben Lockhart,
University of Minnesota, as a relatively new one. It is of
the genus Potexvirus, and named Hosta Virus X, or HVX
for short. Bonnie Blanchette, who is well acquainted with
Dr. Lockhart�s work, has written articles about this virus
in The Hosta Journal and very recently in Fine
Gardening magazine (May/June 2004). There are
pictures of the symptoms in the AHS booklet The Hosta
Adventure (page 28) and now in a link on the front page
of Hosta Library (www.hostalibrary.org). They are
something we should all get used to looking for in our own
hostas and in nurseries.
In the years since my first sighting of this new problem
I have seen more and more plants with the same
appearance turning up in nurseries and garden centers
everywhere I go. Some people have even named forms of
�Gold Standard� that show symptoms of Hosta Virus X.
Chris Wilson, owner of retail hosta nursery Hallson
Gardens in Brooklyn, Michigan, became concerned about
plants of �Striptease� and �Sum and Substance� he had
purchased and began having them tested by Dr. Lockhart.
The ones showing the classic symptoms tested positive
for HVX, but the more frightening news was yet to come.
He sent samples of apparently clean and symptom-free
plants from the same batches and they also tested
positive. What this means is that you cannot visually
identify plants carrying the virus, and that all plants in
batches that have symptomatic individuals might well be
infected too.
As these obviously virus infected plants are showing
up everywhere, the implication is that there are 5-20 times
as many out there that do not show the visible symptoms
of the virus. At this time there may be tens of thousands
of hostas now infected with HVX being offered for sale
in nurseries and garden centers around the world.
The most commonly seen symptoms are found in gold
and gold-centered plants. It is generally random green
mottling, almost always accompanied by mottling that
follows the veins. It often has the appearance of ink on
blotting paper soaking out from the line along the vein.
Other symptoms may also show, and we are still trying to
get a clear idea of what the virus looks like in plants with
green leaves and green centers. Dr. Lockhart says there
may be a variety of symptoms with very different
appearances. Because of this, any plants showing signs of
any viral infection should be immediately disposed of.
Nurseries that have brought in any batches of hostas that
include infected plants should destroy or return the entire
batch as infected, not just the symptomatic plants. Testing
each one would outweigh the cost of throwing
them away.
It should be obvious to anyone that the sheer number of
infected plants we are seeing marks Hosta Virus X as a
clear and present danger to the hosta gardener and
commercial grower. There simply would not be so many
virused plants out there if the virus did not spread easily.
HVX is spread by contact of the sap of infected plants
with healthy plants. This will occur when cutting the
infected plants � not just rhizome division but also cutting
leaves and scapes. Lawnmowers or string trimmers will
also move sap around as will stepping on the plants or
injuring them in any way. Pieces of roots left behind from
digging the plants may also harbor the virus. All parts of a
hosta infected with HVX should be regarded as carrying a
highly contagious virus and handled with this in mind.
Hands and any tools used on these plants should be
sterilized before contacting any healthy plants. The virus
only exists in living plant material. It will not be present in
the soil, so new plants may be planted where a virused
plant was dug as long as there are no still-living roots
remaining there.
It�s never good news to find out about a new threat to
the health of our plants, but it is never something we
should ignore either. With something as easily spread as
HVX appears to be, we must be extremely careful
handling these plants or we will find ourselves spreading it
to the healthy plants in our gardens. It may be tempting to
pick up that fancy new �sport� at the local garden center,
but if it looks like it might be sick, we should keep our
distance from it just like we tell children to stay away
from sick animals.
Never buy a hosta that has a mottled pattern that looks
like little separate islands of another color when the leaf
should be solid color. Named introductions from large
nurseries like �Revolution� are safe, but do not assume a
�Gold Standard�, �Striptease� or �Sum and Substance� with
irregular mottling is safe to take home unless you are sure
you know the difference between mutation-caused
variegation and markings caused by plant diseases. Even
if you think the plant might just be mottled like �Cynthia� or
�Filagree�, leave it alone as it is too hard to be sure
without having it tested for HVX.
This is a disease we can all watch for and do
something about. If you see that friends have purchased a
virused hosta, impress upon them the importance of
getting rid of it before they start unknowingly spreading it.
If you see that a nursery or garden center has plants that
show Hosta Virus X, tell the manager or owner that it is a
virus that can be spread. All plants infected with Hosta
Virus X should be destroyed as soon as possible
since there is no cure and it is contagious. Explain
that this is a new virus and word is just getting around, and
the supplier it purchased the plants from will hear about it
soon if it hasn�t already. Unlike foliar nematodes, Hosta
Virus X can be stopped from becoming the next hosta
plague if we all act quickly. Now is the time to start.

View Photos of Virus X- infected plants at www.Hostalibrary.org