What Is Dahlia Mosaic Virus And How To Control It

If you notice that your Dahlia seems stunted, twisted, and blotchy, you may have a Dahlia Mosaic Virus (DMV) case on your hands. This virus is spread through the plant sap and causes severe disfigurement of Dahlia plants.

The virus may be carried from plant to plant by aphids or on plant care equipment (e.g., hand pruners) that has not been properly sterilized between plants. This article discusses DMV and shares advice on controlling it. Read on to learn more. 

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What Is Dahlia Mosaic Virus?

DMV is a caulimovirus, and there are three separate strains of it: 

  • DMV-Portland 
  • DMV-Holland
  • DMV-D10

A plant can carry all three strains at once. However, the DMV-D10 is most frequently found in the seed. 

How Do You Know Your Dahlia Has DMV? 

There are several symptoms you should watch for when attempting to detect this virus. Be advised the severity of the symptoms may vary depending upon the type of Dahlia you have. Symptoms include: 

  • A virus may stunt the overall size of the plant. 
  • The tuber and roots may develop poorly. 
  • Flowers and their stems may be noticeably small. 
  • A virus may reduce flower production. 
  • Leaves may be cupped or rolled, twisted, and stunted. 
  • Black, rotten (necrotic) spots may appear near the leaves’ mid-vein.
  • Yellow and pale green streaks on the leaves’ mid-veins and branch veins are caused by a loss of chlorophyll. 

It is not always possible to detect the presence of DMV by symptoms because some plants may carry the virus and remain asymptomatic. 

To further complicate matters, Dahlias are also subject to infection by other types of mosaic virus, such as:

  • Tomato Spotted Wilt
  • Tobacco Streak

For home gardeners, distinguishing between these viruses is not especially important. 

Commercial growers can make a precise diagnosis by submitting samples of infected plants to a plant pathologist who will determine using antibody-based or molecular testing. This is especially advised for growers who overwinter tubers or collect and save seed for year-to-year production. If you want to have your plants tested, contact your County Agent for instructions. 

What Can You Do To Kill The Virus?

The best you can do with all viruses is to prevent their spread. There is no cure. If you notice symptoms developing in one of your plants, quarantine it as quickly as possible. 

Because this virus spreads through the sap, it can only travel from one plant to another if a vector, such as aphids carry it, or it spreads by unsterilized gardening equipment, or if sap from a damaged plant comes in contact with another plant. To prevent this, follow these tips: 

1. Don’t let aphids (or other sap-sucking Dahlia pests) get established in your garden. When these little sap-suckers make a meal on an infected plant and then move to a non-infected plant, they carry the virus with them. 

To keep aphids under control, keep your plants healthy; encourage natural predators; use horticultural soaps as needed when aphids are observed. Chemical insecticides are not recommended because they are not especially effective against aphids. The pests do not stay in place long enough to have significant contact with the toxins. 

More on dahlia pests here.

2. Quarantine new plants for a couple of weeks before introducing them to your collection. 

3. Quarantine plants that have a mosaic virus. For complete control, destroy these plants. 

4. Never use seed, cuttings, or tubers from plants infected with DMV for propagation. 

5. Wash your hands often when handling Dahlias. If you can’t do this, consider wearing disposable gloves and changing them between plants. 

6. Thoroughly disinfect your hands and gardening tools after contact with a diseased plant. 

7. Disinfect your gardening tools between plants when performing routine maintenance, such as deadheading flowers, pruning, tuber division, and the like.

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