Hosta viruses have been known to exist since at least 1985. Dr. Ben Lockhart of the University of Minnesota, the leading researcher on viruses in hostas and first to isolate Hosta Virus X, has found four different viruses that are pathogens for hosta. Dr. Lockhart has concluded that plants cannot be cured of viruses, so the best remedy is for any hosta exhibiting a virus to be destroyed. Until recently, and consistent with the research done by Dr. Lockhart and funded by the American Hosta Society, viruses spread slowly and are not easily transmitted in the garden.
However, now there is more frequent appearance of mottled hostas in large general nurseries and “box” stores that sell plants to the public on a large scale. The increase appears to be due to mass propagation of hostas infected with the virus, thus also allowing the virus to be propagated with the plants. This has resulted in a heightened concern about Hosta Virus X. (See the separate section on HVX.)
The American Hosta Growers Association, AHGA, has regularly advised its members of the problem, most notably after the recent increase in hostas exhibiting the virus. “Hosta Virus X, HVX, has been seen in many hostas in bare root stock purchased from overseas . . . especially in plants of ‘Sum and Substance’ and ‘Gold Standard’. Other Hostas with the virus include ‘Golden Tiara’, ‘Wide Brim’, ‘Birchwood Parky’s Gold’, ‘Diamond Tiara’ and ‘Striptease’.” This is not to say that these plants are the culprits rather that these are the plants that have exhibited the virus and, if they are being purchased, they should be carefully inspected beforehand.
The AHGA recommends that its members do two things if they receive material that appears to have the virus. First, “removal of diseased plants is the best control measure.” Second, “if you have any hostas that are showing symptoms, it is suggested that you notify your supplier. The more complaints, the more pressure we can bring to help get this problem cleaned up quickly. It is also suggested that you ask for your money back and not accept plants next year as replacements.”
This heightened concern has also been seen in recent national publications. In an article in the June 2004 issue of Fine Gardening, Bonnie Blanchette (an AHS member who works closely with Dr. Lockhart), described Hosta Virus X as a pest problem on ‘Golden Tiara’. In discussing this article, the AHGA indicates “In the photo, note that the virus discolors the leaf in a different way than it does in gold hostas. (On gold hostas the virus usually produces green streaks.) HVX is becoming more common in hostas, so beware. Destroy any hostas that show symptoms and please notify any growers that may have sent you infected plants so that they can clean up their stock.”
Normal symptoms of viruses include irregular blotchy patches of lighter or darker tissue, circular spots with rings around them, and small lighter flecks. Different viruses are spread by the sap of an infected plant coming in contact with an open wound in a clean plant. This can be from tools that were not disinfected between use in dividing plants, or pruning tools used to cut the scapes from different plants without disinfecting them between use. The virus can spread from an animal or insect feeding on an infected plant, then feeding on another plant. A professional diagnosis of plants showing suspicious symptoms would be advisable. From that, the professional should be able to tell you how the particular virus would normally be spread and what other plants may be hosts. Eliminating the infected plant and controlling the potential spread of virus vectors should help preserve the remaining plants.
We are probably observing more diseases in our hostas than 20 years ago for three reasons. The simple reason is that we are hopefully more aware of the diseases. We may also be inadvertently sharing our plague with our friends if we do not scout out diseases. Remember, some infectious diseases can be difficult to detect, especially when the organisms are present in very low numbers. The other reason is that our hosta gardens have become a more dense population of similar plants. In any situation where population density increases, the chance for infection is greater. If one susceptible individual contracts a disease, it is more easily transmitted to others in a denser population. There is more contact between healthy and diseased individuals. If we each had only two or three hostas in our garden, instead of 200 or 300 or more, we might not have as many diseased plants.
With this background in mind, the purpose of this policy is to persuade our members to do the following:
Understand what virus symptoms look like.
Destroy any infected plants they may have in their collections and not spread the disease.
Quit buying and encouraging sales of virus-infected plants.
Help inform others who may have infected plants that there is no cure, and that the plants should be destroyed and not sold.
Quit registering virus-infected plants.
This policy discussion should be featured prominently on the AHS Web site and in The Hosta Journal and mailed to all newsletter editors, regional directors, speakers, Internet lists, and others who relay information to the general membership. We also intend to work closely with the AHGA in monitoring and addressing the virus issue.
- We believe the majority of the sampled plants showing infection have been HVX, but if those plants are not indexed we cannot be sure. What we can easily say is that there are numerous sightings of mottled foliage on hostas, and that FREQUENTLY this is caused by a virus. According to Dr. Lockhart, some plants may remain symptom-less. Some hostas may flip between showing symptoms and not.
- Mottled-leaved hostas should be assumed to be infected with a virus and, even if tested negative, they should always carry that suspicion.
- There is no cure for plant viruses once a plant is infected. Plants do not have any kind of immune systems that can be used to one day eliminate the virus. We cannot expect there will ever be a cure. Plants that exhibit virus characteristics should be destroyed.
- Unless the plant owner has a certificate from a certified testing lab that states the plants to be free from viruses after having been tested three times over as many years, plants that exhibit virus symptoms should not be accepted for AHS auction or be sold at sales tables at AHS conventions. This does not mean vendors can’t sell plants that exhibit viruses; it just means they can’t sell them at AHS functions.
- Virus-infected hosta leaves should not be entered in a Hosta Show to be judged. Leaves that exhibit virus characteristics and that have not been registered as having such patterns may be disqualified by the show chair. Judges should exhibit care in not attributing high “distinction” scores to plants that may be simply exhibiting virus characteristics. However, these plants may be entered in the educational section to educate attendees about hosta viruses and what to look for, along with information on the risks associated with planting them in the garden and how to eliminate them from the garden.
- Hostas exhibiting virus characteristics should not be registered without having been tested. As noted by researchers, a plant may not test positive yet still have been infected; i.e., that the virus was not “active” at the time the plants was tested. A virus-free test means you did not get a positive test for that specific virus at that specific time. Thus, if a plant does not test positive for a virus in a given year, it does not necessarily mean it is not infected. It should be required to be tested three times in as many years with the results to be submitted with registration showing the lack of active virus over that period of time. It does not do the registrar, nor the members, any service to register unhealthy plants. While registration is not a certificate of garden worthiness, it does have an implication of sucH. When a plant appears to be infected with a virus, the registrar should advise the registrant not to be associated with such a plant and recommend that the plant not be registered. Further, the registrar should insert a caveat in the Registration Issue that states something like “this cultivar, both through description and photography, shows many of the symptoms of virus infection.”
- AHS will assemble a package that at least points to available information, including photos of diseased plants, on the Web or in other publications and make this package available to all, either separately or as part of a unified pest and disease package. Further, nurseries and garden centers may be reported to the VP Genus Hosta, who will mail out information to the affected nursery.
Remember no one has gotten rich and become famous from introducing one, or for that matter several, new and exciting hosta that took the world by storm. On the other hand, if that new and exciting mottled hosta that took the world by storm were virused, that introducer could become infamous! Don’t panic. This problem is easily removed from the garden and with diligence should not overrun our hosta collections.