For a long time, hostas were considered a "caste iron" plant that had no serious problems other than deer and slugs. Now that millions of gardens contain hostas, people around the turn of the century, started noticing weird looking plants. Upon laboratory analysis, many of these plants were found to be infected by plant viruses. Ugh!

Bad News and Not So Bad News - The bad news about plant viruses is that, once the plant is infected, it cannot be cured. (Well, let's say, that for all practical purposes, it can't be cured. There are a few extremely tedious propagation techniques which could create a new plant from a tiny, uninfected part of the plant.) There are no sprays or chemical treatments for a virus problem.

Generally speaking, the only recommendation for managing an infected plant is to remove it from the garden and destroy it. That can be expensive. That is why prevention is the only practical course for stopping this problem in your garden.

The not so bad news is that virus infections do not necessarily mean the death of the plant. Viral disease in plants usually show themselves in mottled (yellow) streaks in the leaves, distortion of leaves or other plant parts, flower abortion or discoloration and loss of overall vigor in the plant.

Another not so bad news element is that viruses do not easily spread through your garden.

How do viruses spread? Fortunately, viruses are immobile "crystalline" type of organisms. In other words, they don't have legs or wings and cannot swim. They must rely on others to move them around. Some plant viruses need the help of sucking insects such as aphids, thrips or leafhoppers to move them from plant to plant. Others are transported on the surface of pruning shears or hoes that cut one plant and then move on to cut another plant. A few viruses can move in splashing water from rain or irrigation causing a splash that goes from one plant to another.

Do all hostas get viruses? NO! Research to date indicates that some hosta cultivars are susceptible, some are tolerant of viral infection i.e. they may test positive for the virus but show no symptoms and others appear to be immune. Hostaphiles are in the process of defining which cultivars belong to which group.

The American Hosta Society has been helping to fund research on hosta viruses by Dr. Ben Lockhart at the University of Minnesota. Here is a summary of what he has found out so far on several virus types found in hostas:


1. Hosta Virus X
- This virus only infects hostas causes mottling, deformation and white flower breaks in purple flowering hostas. The mottling shows lighter blue, green or yellow markings that start in the leaf veins and bleed out into surrounding areas. Dark colored tissue may have a bleached out appearance.

It is spread by mechanical means which spread infected sap such as pruning tools or tools (including your hands) used during division of clumps or deadheading flower scapes. In some cases, it is speculated that it may take up to a year or more for symptoms to appear after the plant has been infected.

A lot of people wonder about the spread through tissue culture (TC) but this is considered an unlikely possibility. Under the sterile conditions that must be maintained in TC, testing for virus contamination is a matter of routine in most labs.

So far, this virus has not been found in seeds or pollen. Also, it appears that it is not spread by insects such as leafhoppers.

If this infection is present in the garden, sterilize tools with a 10% bleach, 90% water solution between using on different clumps of hosta.

If you suspect Hosta Virus X is in any of your plants, contact your local Extension Service office or a plant lab at the state university for testing details. If your sample is positive, you need to immediately remove the entire infected plant(s), not just the foliage, and destroy them. You can burn them (if permitted), bury them in a deep hole or send them off to the landfill.

Note: Results of recent research indicate that the virus can continue to remain active in the soil so do not replant in the same soil. Additional research in studying how long the virus remains active while in the soil outside hosta tissue. Check the American Hosta Society website for the most current research results.

Susceptible Hosta Cultivars:

Many but certainly not all hosta cultivars have been tested for Hosta Virus X over the past couple of years. A relatively small number of cultivars have tested positive for one or more plant samples indicating that they are susceptible to this virus.

The cultivars listed below have had at least one plant test positive for Hosta Virus X. This DOES NOT mean that ALL of the plants in this cultivar HAVE the virus. It just means that you might want to keep a special eye on them. Tens of thousands (or more) of each of these cultivars are growing perfectly healthy lives in gardens across the nation.

Hosta Cultivars Caused by a Virus

The mottled color effect caused by viruses may sometimes appear to be just another unusual form of variegation. As a result, several hosta cultivars have been introduced which, upon further examination, owe their coloring to a virus. Some may be infected by Hosta Virus X but other viruses may also cause this effect. The key appears to be that mottling caused by a virus will appear to "bleed" out from one of the veins of the leaf. Mottling of healthy plants is spread out more evenly across the leaf blade. Such cultivars should not be grown in the garden. They include:

Virus Free Mottled Cultivars

There are several hosta cultivars that have interesting mottling effects on their leaves that DO NOT test positive for the Hosta Virus X. These include:

  • 'Wild Bill'
  • 'Wolcott'
  • 'Xanadu Paisley'


2. Tobacco Rattle Virus (Tobravirus) -
This virus infects a wide range of commonly grown garden perennials and causes discoloration, irregular lesions and necrosis (death of tissue). This one is transmitted by soil nematodes (microscopic roundworms) and may also move in the seeds of infected plants. Usually, if you remove all the infected plants and grow annuals or leave the soil bare for a year or two, this type will be eliminated.


3. Tomato Ringspot Virus -
A wide range of plants including elm trees and tomatoes may be infected by this virus. On hostas, it shows up as small white spots often with concentric rigns, blanching of leaves and may be mistaken for symptoms of iron deficiency.

This virus involves the roots of the plant and its significance in hostas is not yet established. It is transmitted by root feeding critters called nematodes.


4. Impatiens Necrotic Spot Virus and Tomato Spotted Wilt Virus
- Many ornamental plants including impatiens, lilies and others are susceptible. It shows up as a series of yellow or brown circles.

This virus is spread primarily by an insect called thrips (its the same whether singular or plural) which suck juices from one plant and take it to another. This happens primarily in the greenhouse so it is imperative that this pest be controlled in this environment. It may also be more prominent in the warmer areas in the Southeastern United States.


5. Arabis Mosaic Virus -
Again, this one infects a wide variety of plants and causes a symptom called chlorotic flecking and brown lesions. It spreads by nematodes and infected seeds. So far, this virus has been found only once in the U.S. and the affect on hostas in the garden is not known.

Virus Infected Hosta Leaves

 

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