Our continuous improvement approach to controlling and reducing dahlia virus in our gardens
Dahlias are prized for their stunning blooms and the wide variety of shapes and colors they come in. The first year or two in growing dahlias the blooms capture most of your attention. However, after growing dahlias for a year or two your eye becomes more aware of the plants and the differences from plant to plant and leaf to leaf. Most of those differences can be attributed to insects, nutrient deficiencies, or virus. When you see stunted plants, odd shaped leaves, yellow blotching on the leaves, or yellowing of the veins of the leaf these are common signs of virus in your dahlias. And like all plants, dahlias are susceptible to viruses, which can impact their health, vigor, and flower quality. And once infected, the plant will carry the virus until it dies. Thus, virus management is critical for maintaining a thriving dahlia collection.
It is important to understand that virus transmission - transmission of virus from clean(virus free) plants to infected(virused) plants is a key cause of increased virus in dahlia plants. This occurs via 3 primary means.
One way dahlia virus is spread is through insects. Specifically, insects with piercing, sucking mouth parts such as thrips and aphids. An insect can ingest an infected plant and then move to a non-infected plant and infect it.
A second way dahlia virus is spread is via humans. When using flower snips or other hand tools and transferring infected flower sap from one plant to the next when cutting flowers, cutting plants, or when dividing tubers. Fortunately, this is a means we can control and mitigate this risk of virus transfer by adjusting our processes.
A third way virus is spread is by adding infected tubers or plants into your garden. We all like to by new varieties to add to our garden each year and this creates an opportunity for virus to enter your garden as well.
As you can see, virus can be transferred fairly easily between plants. The data that the ADS has shared is that 87% of dahlias are infected with a virus. And that is broken down to the following viruses. Depending on what data you look at, 75 to 84 percent of our dahlias are infected with Dahlia mosaic virus(DMV). The next most common virus in dahlias is Tobacco streak virus(TSV) with data showing 35% of dahlias being infected with TSV. Tomato spotted wilt virus(TSWV) is infected in 2-6% of dahlias and then Impatiens necrotic spotted virus(INSV) infected in 1-2% of dahlias.
With numbers like this preventing virus in dahlias can seem overwhelming and impossible. But, the ADS gives us some guidelines that if applied can give us some hope. The three recommendations they make are disinfect your tools, pull out any plants that show virus symptoms, and most importantly start with clean stock. I discuss each of these in more detail below.
1. Use a 10% Bleach to water solution anytime you will be using a cutting device, cutting flower blooms or for dividing tubers.
• Bleach Solution Preparation: Mix a 10% bleach solution by combining one part bleach with nine parts water.
• Usage: Dip your cutting tools (e.g., pruners, knives) into the solution before moving to the next plant. Let the tools sit in the solution for 2 minutes before using.
• Why It Works: This simple step kills viruses on your tools, preventing their transfer to healthy plants.
By integrating this practice into your routine, you’ll significantly reduce the likelihood of virus spread during the growing and dividing seasons.
2. Pulling Suspect Dahlias During the Growing Season
Early detection and removal of suspect plants are crucial to managing virus outbreaks. The American Dahlia Society (ADS) recommends removing and destroying any plants showing signs of viral infection.
• Signs of Viral Infection: Look for symptoms such as stunted plants, odd shaped leaves, yellow blotching on the leaves, or yellowing of the veins of the leaf these are common signs of virus in your dahlias.
• Protocol: If you suspect a plant is infected, carefully remove it from the garden, including the tubers. Dispose of it in the trash—do not compost infected plants, as viruses can persist in compost and infect future plants.
• Why It Matters: Leaving infected plants in your garden increases the risk of viruses spreading to healthy plants via thrips, aphids, leafhoppers, or other vectors. Removing these plants promptly helps contain the problem.
3. Start with clean stock
The best way to minimize the presence of viruses in your dahlia population is to start with clean, virus-free stock.
Much time is spent talking about purchasing from trusted sources. And while it makes sense to keep sources without any virus management protocol from your garden, I have received virused stock from trusted sources and it makes sense that this happens and will happen if 87% of dahlias are virused that 87% of tubers are virused. And reducing the spread of virus and pulling plants that visually show virus signs aren’t robust ways to reduce the amount of virus in one’s garden.
In my opinion, the best way to get virus free dahlia tubers is if an effective testing program is in place. Only then can the tuber be certified as virus free. But, testing costs are prohibitive and 100% testing is not a realistic option. Agdia.com is a company that provides testing options and is a great tool to help determine virus trends in your gardens. This then leads us to virus free dahlia cuttings. Knowing these cuttings are virus free we then know this subset of plants in our garden is virus free and thus reducing the amount of virus in our gardens and thus reducing the amount of transmission.
Benefits of Virus-Free Plants: Starting with clean stock reduces the baseline percentage of infected plants in your collection. Over time, this practice can significantly improve the overall health and performance of your dahlias.
For instance, in 2022 I we did not plant any virus free cuttings in our gardens. I then have to assume that likely 87% of our plants had virus, the Industry average. But in 2023, 24% of the dahlias planted in our garden were from virus free cuttings. If 24% of the plants had 0% virus and the other 76% of plants 87% were infected with virus our gardens became less virused overall from 87% virus plants in our garden to 69% virused plants. Now, that is a significant improvement and improvement in the quality of our products!
So, if we want to reduce the amount of dahlia virus in our gardens and improve the quality of our plants and tubers we must have a strategy to introduce virus free cuttings into our garden every year and to control the transmission of dahlia virus. The below is our current strategy. It feels like there are a number of iterations we can do to continue to improve our strategy and we plan on testing at the end of the summer, evaluate the results, and then adjust our strategy again. We are excited to see and share the results with you as we continue to improve!
Final Thoughts
Managing dahlia viruses requires vigilance, but the rewards are well worth the effort. By implementing these strategies—sanitizing tools with a 10% bleach solution, removing suspect plants promptly, and starting with virus-free stock—you can enjoy healthier plants and more vibrant blooms year after year.
For more resources and tips, visit the American Dahlia Society, which offers valuable guidance on maintaining a thriving dahlia collection. By taking proactive steps to reduce viruses, you’ll create a more resilient and beautiful garden.
Happy gardening!