Hosta Virus X (HVX)
Many hostas are turning up that are infected with a virus called Hosta Virus X (HVX). The most commonly seen ones are plants of ‘Gold Standard’, ‘Striptease’, and ‘Sum and Substance’, but other common varieties are being reported infected in large numbers. While this disease does not kill plants, its primary danger lies in its proven ability to spread prolifically. Because symptoms may take years to show after infection, HVX has infected hundreds of thousands of plants and is at epidemic levels around the world. If a batch of hostas contains any individual plants that show HVX symptoms, the whole batch should be considered infected and should be destroyed, as individual testing is impractical and not a guarantee.
If you are a gardener, do not buy plants from batches that show even the slightest markings on even one plant. If you have these plants from batches that show symptoms at your home, dispose of them immediately. If you are a grower or vendor, learn what the signs are and contact the supplier if you see them in your stock. This virus is widely spread at this time in the above plants and others (see table of infected cultivars) and the source nurseries are still learning about the problem as of 5/06. Only testing with the specific ELISA kit for HVX can detect HVX. Very large numbers of HVX-infected plants are still currently being sold at all levels.
This virus is transmitted primarily through cutting the plants. Contact of the infected plant’s sap with sap of a healthy plant will infect the new plant. This can happen whenever cuts are made and the instruments or hands are not disinfected afterwards. Dividing hostas, removing bloom scapes, removing leaves, stepping on them, even accidentally running the lawnmower over them can and will spread this virus. It survives only in living plant tissue and dies without a host. Plants in pots may be simply disposed of or burned. Plants in the ground should be dug carefully as to get as many roots as possible, and the spot should not be replanted until any remaining roots have died and rotted away.
Southern Blight is caused by the fungus known as Sclerotium rolfsii. Flutolanil is a relatively new fungicide (last 6 years)that has proven to be an effective prevention and curative of plants with the disease. Many fungicides are now available which contain flutolanil (in various concentrations) but not all are labelled for use on ornamentals. Some identical products, such as Scotts Contrast 70WSP and ProStar 70WP, are identical but sold under different labels. Here are some links which may be helpful.
This first article by Iowa State University introduces the reader to this fungus as found on hostas and mentions the fungicide flutolanil:http://www.extension.iastate.edu/Publications/SUL8.pdf
The next link is the label on Scotts Contrast 70WSP. You can see that it’s for treating (preventative and curative) the fungus Sclerotium rolfsii, and that it’s labelled for use on ornamentals: http://www.scottsprohort.com/_documents/tech_sheets/H4586_Contrast_95216.pdf This last link is for Bayer ProStar 70WP, which is also labelled for Sclerotium rolfsii: http://www.cdms.net/ldat/ld24E001.pdf
For anyone who has battled Southern Blight before, you should thoroughly clean your beds in the fall, making sure their hostas are planted high in the ground (mounded up rather than in a hole), and that their hosta garden receives adequate ventilation (trim tree branches up, etc.). Think about applying the Contrast or ProStar to the affected areas in early spring as the hostas are just popping up is a good preventative for dealing with the problem later on in the summer.