When we say “new” in the world of plants, it’s often something that originated within the past 20 years, but has only recently come to the forefront. For example, a “new” plant variety might have been bred 20 years ago and took decades to test and reach the retail market.
A very serious “new” disease is affecting the popular perennial hosta. It was first identified about 20 years ago, but is now becoming a widespread and damaging epidemic, identified in most states including North Dakota and Minnesota, and many of us have only recently become aware of it.
The disease is caused by a virus, and has been termed Hosta Virus X disease, abbreviated HVX. For information about the disease, I researched North Dakota State University, University of Minnesota, Wisconsin State University and others. The most recent information I found was written by Illinois State University July 5, 2017, and much of the following information is based on that literature, supplemented by the others.
The HVX Problem:
- The symptoms tend to be subtle and not always easily identified.
- Plants infected with the virus can be carriers of the disease even if they don’t show symptoms, but they can pass the disease to other hosta plants.
- Plants infected with the virus might not show disease symptoms for a year or two.
- Hosta plants are being sold that contain the virus disease, some showing symptoms, some not.
- Only hosta are affected by this particular virus; it doesn’t travel to other perennials.
- Many perennial gardens and landscapes are now harboring HVX, unbeknownst to their owners.
Symptoms of HVX Disease on Hosta Plants:
- The virus doesn’t usually kill hosta plants, but it can.
- Symptoms can be subtle; look for leaf patterns or markings that aren’t characteristic of the hosta variety.
- Symptoms vary between the many different hosta cultivars.
- Look for light or dark green discoloration along leaf veins, referred to as “ink bleed.”
- Look for mottled yellow/green pigment, mosaic patterns, puckering, circular ring spots, necrotic dry dead leaf tissue, wilting and sometimes death.
- Leaves are sometimes stunted and distorted.
- Sometimes only one or two of the symptoms appear, not necessarily all of those described.
- Overall health of the hosta plant generally declines over time.
- Plants that are seemingly healthy can still be carrying the virus internally.
Where does the disease come from, and how is it spread?
- HVX is usually introduced into an established hosta planting when new hosta plants are brought in. The new plants might be infected, but not yet showing symptoms.
- The disease is not known to be spread by insects.
- HVX is spread by infected sap that gets transferred between hosta plants on hands and pruning tools.
- The disease is easily spread when hosta are divided and distributed between friends and neighbors.
- Many retail outlets are unknowingly selling infected plants, especially mass merchandisers.
What can be done? Is there a cure or treatment?
- Once a plant is infected, there is no cure. Infected plants should be dug and destroyed by burning or disposing in landfill.
- When an infected hosta is removed, carefully remove all root pieces, and wait at least a year before replanting a hosta in the same spot.
- There are no immune hosta varieties.
- There are no chemicals that prevent or treat HVX.
- Carefully wash and sterilize tools and hands when working with hosta.
- Avoid sharing hosta divisions with fellow gardeners.
- Simply removing leaves that show symptoms doesn’t work, as the virus is in the sap flowing through the entire plant.
- Buy hosta only from reputable garden centers that might know if their stock has been virus-indexed or tested. Remember that even plants with no symptoms might be carrying HVX disease.
- Garden centers and hosta wholesalers can test their stock to ensure it’s free of HVX, using a product called ImmunoStrips by Agdia Corporation.
- Other than testing, there is no foolproof way of telling whether a hosta you’re purchasing is infected, unless of course, you see symptoms.
- The disease is possibly less active in late summer and fall, when hostas are done blooming, which might be a better time to divide or transplant hosta, than spring or early summer when the virus is most active.
This disease is a serious problem because of the sheer numbers of hosta contained in perennial gardens and landscapes.