Monitoring Dahlia Viruses and Maintaining a Clean Dahlia Garden

As I start my 2026 dahlia season, I am planning on adding more dahlia testing to the cost of growing my dahlias.  I do monitor for virus, grow mostly dahlias from seed, and I always use a sanitized tool to cut each dahlia plant.  I have grown named dahlia cultivars from other breeders in previous years.  Here is an updated blog post about dahlia viruses and my plans for this year.

Understanding Dahlia Viruses

As the dahlia season begins, it is important to be aware of the various viruses that can affect your dahlias.   There are around a dozen viruses that can infect dahlias.   The most common is Dahlia Mosaic Virus (DMV), which is a DNA virus.  The most prevalent RNA viruses are Tobacco Streak Virus (TSV) and Tomato Spotted Wilt Virus (TSWV).  Thrips and aphids are the primary pests associated with virus transmission.  Dahlias and viruses have co-existed for hundreds of years, so it is crucial to stay informed and continue efforts to minimize virus spread.

Virus Transmission and Host Plants

TSV and TSWV are both spread by thrips.  TSV has over 200 plant species that can serve as hosts, including tomatoes, soybeans, sunflowers, cotton, peanuts, roses, impatiens, echinacea, dahlia, jimson weed, field bindweed, black nightshade, and mustard weed.  TSWV has an even broader host range, with more than 1,000 species such as tomatoes, peppers, tobacco, peanuts, potatoes, impatiens, chrysanthemums, dahlias, zinnias, petunias, peonies, chickweed, dandelions, field bindweed, and thistles.  Thrips can ride air currents and enter your garden overnight, especially in warmer, tropical weather.  These small, slender insects puncture plant tissues, causing damage and spreading viruses.  As larvae, they feed on infected plant material and become vectors, transmitting viruses as they mature and feed on healthy plants.

Symptoms of Virus Infection

Tobacco Streak Virus can cause stunted growth, leaf deformation, downward leaf curling, black streaks, or necrotic ring spots on leaves.  Tomato Spotted Wilt Virus may result in stunted growth, wilting, curled or distorted leaves, yellow spots, and petal discoloration with lines or ring patterns on leaves.  Loss of the normal green color along leaf veins is a key symptom to look for.

Garden Layout and Weed Management

Because TSV can infect so many plant types, keeping your dahlia garden separated from other perennial beds, vegetable gardens, and unmowed areas like meadows is important.  Managing TSV is particularly challenging because it can persist in surrounding host plants like echinacea.  I am glad my dahlia field is around 300 feet from my house where I have some flower beds with perennials like echinacea or rudbeckia.  My neighbor has a large open field that he mows twice a year.  The weeds that bloom in my neighbor’s field are attracting beneficial insects, but they can also attract thrips, so I am relieved that I am at least 125 feet away from his field to help reduce the risk.  Controlling weeds in and around your garden is crucial, as weeds can host thrips.  Regularly mowing grass and removing plant debris from the dahlia garden helps minimize thrip and pest habitats.

Monitoring and Controlling Thrips and Aphids

Yellow sticky cards can be used to monitor thrip activity around your dahlias but be cautious as they can also trap beneficial insects.  For aphid control, spraying the tops and undersides of leaves with insecticidal soap can help deter these pests.  Thorough coverage of leaves is necessary when using insecticidal soap.  Insecticidal soap is organic but can harm small beneficial insects on contact, so avoid spraying blooming plants to protect pollinators. 

Insecticide Application Strategies

If thrip infestations are problematic, apply insecticides at five-day intervals until populations decline, then continue applications every seven to ten days.  Alternating between different insecticides is essential to prevent thrips from developing resistance.  Even organic insecticides can harm beneficial insects.  Spinosad is a natural bacterium suitable for organic gardening and effective against thrips.  It should be applied when temperatures are between 65–85°F, ideally in the early morning or late evening.  Horticultural oils are less toxic than chemical pesticides but are not selective and can harm beneficial insects so be careful using any product.

Timing and Techniques for Insecticide Use

Treating dahlia cuttings with a systemic insecticide that control thrips before planting in the garden is an effective approach.  At the start of the dahlia season, applying a systemic insecticide early to young dahlia plants helps control insect populations before they escalate.  Systemic insecticides are absorbed by the plant in their leaves.  Some products are Bonide Systemic Insect Control and BioAdvanced Insect & Disease & Mite Control.  As the dahlia season progresses, changing to products with Spinosad helps with resistance and control of insects.  To protect pollinators, spray insecticides in the evening when fewer beneficial insects are present.  Once dahlias begin blooming, I refrain from using insecticides to avoid harming pollinators.  If a severe thrip infestation occurs during blooming time, I cut back the flower blooms before considering insecticide use, encouraging thrips to leave and reducing chemical intervention.  Thrips often hide deep within the flowers and buds.  Always sterilize cutting tools with disinfectant between plants.

Preventing Virus Spread and Tool Disinfection

DMV is primarily spread by aphids and by gardeners who do not disinfect their tools.  Symptoms include yellowing along leaf veins and reduced plant performance.  On the American Dahlia Society website, there is a report from March of 2023 from research and testing in 2022 of dahlia leaf samples that indicated a positive rate of at least 70% for Dahlia Mosaic Virus (DMV).  Asymptomatic plants can still be infected and may transmit the virus to others.  Separating named dahlia varieties from your dahlias from seed by 10–20 feet can help reduce infection.  Regular tool disinfection is vital, as viruses are transferred via contaminated plant sap.  Use a 10% bleach solution (as recommended by the American Dahlia Society) or Virkon S disinfectant, which is less harsh on tools.  Bleach solutions lose effectiveness after about two hours.  I use Virkon S disinfectant as it is a powerful, broad-spectrum disinfectant that kills viruses, bacteria, and fungi.  It is used for cleaning and disinfecting hard surfaces in transportation, veterinarian offices, and livestock production facilities.  LANXESS Corporation manufactures Virkon S disinfectant.  Per Lanxess.com, Virkon S has been proven effective against 64 strains of virus, 35 strains of bacteria, 5 strains of fungi, and 15 plant pathogens.   Virkon S contains potassium peroxymonosulfate.   Ten minutes is the maximum contact time, so I keep my cutting shears in the solution for 10 minutes to kill any virus.   Virkon S has been proven to act against certain viruses in as little as 15 seconds to 5 minutes.   For a 1% solution, you use 1 tablet per 2 cups (16oz) or 2 tablets per quart (32oz).   The pink color indicates the solution is active.   If it turns pale or clear, it is no longer effective.   I have read where the prepared solution is stable for several days; however, I use a fresh solution every time I am disinfecting my tools.   I do not reuse it the next day.

Virus Testing

Home virus testing kits for dahlias are available from companies like Agdia, Inc.  Testing typically involves a small leaf sample, and costs can be significant if testing many plants.  False negatives and positives are possible, so some growers test multiple times per season.  Testing in the fall is recommended, as plants may not show symptoms until later in the season.  Mark and store tested plants separately and use them for cuttings the following year.  To reduce costs, some growers combine samples from two dahlias in one test.  When you take a leaf sample, Agdia, Inc. says to only use a one inch leaf sample.  The size of a postage stamp.  If too much plant tissue is used the test will develop slowly or not at all.  Some dahlia growers are cutting that leaf sample in half and testing two dahlias per test and still have accurate results.  This would help me to reduce that cost of testing as 25 TSV tests are currently $190.00 and 25 TSWV tests are $190.00 at Agdia, Inc.  I would be able to test 50 dahlias to bring down the cost to $8.00 per dahlia.  I would mark tested plants and focus testing on those intended for propagation. 

For DMV testing, you would need to send leaf samples to Agdia, Inc.  The current price is around $75.00 for the first dahlia sample and $35.00 for each additional dahlia sample. 

General Practices for a Healthy Dahlia Garden

I like to maintain healthy dahlias through foliar sprays with fish and seaweed products and feed the soil with molasses to encourage beneficial microbial activity.  Healthy plants are less susceptible to pests.  Keep dahlia blooms cut to promote bloom production and tuber development but allow blooms in October for pollinators and seed saving.  Inspect dahlias daily, remove any sick or unusual looking plants, and dispose of them in the trash and not in your compost pile.

Separation and Acquisition of Dahlia Stock

Limit the introduction of new dahlias to your field and isolate new dahlia varieties in grow bags or raised beds to reduce the risk of introducing viruses.  Monitor daily and promptly remove and discard any plants showing signs of disease.

With over 70% of dahlias having a virus, there is a possibility that some of the named dahlia varieties that I have may have a virus.  I only have 40 named dahlia varieties cultivars from other dahlia breeders that I have grown for years.  I do not want to get rid of some of my favorite dahlias like Jersey Beauty, Hamari Gold, and Kidd’s Climax.  I plant those named dahlia cultivars in my first row of dahlias or in nearby raised beds.  I do not plant those named dahlia varieties amongst my dahlias from seed.  I have grown these dahlias for years and I have not seen virus.  I always monitor and inspect my dahlias and disinfect my tools.  ADS has recently suggested to plant your untested dahlias in one area to continue to monitor.  Then plant your dahlias from seed and tested plants in another area maintaining some separation.

Economic Considerations and Supplies

I am retired and maintaining my dahlia field is not a cheap endeavor.  I have twenty 80 foot rows and grow around 2500 dahlias including first year dahlia seedlings.  Growing dahlias at this scale involves considerable annual expenses, including supplies, pest control, irrigation, storage, and website.  When I am selling tubers, there is packing and shipping costs.  Expenses may fluctuate based on weather, pest pressure, and equipment maintenance.  I am trying to incorporate virus testing in my yearly cost of growing dahlias.  This is a guideline that I use each year to project my expenses for the year.  I normally spend around $7,000.00 per year on my dahlia field.  I am planning on adding the expense for dahlia testing.

Item	Estimated Cost
CPA	$400
Drip Irrigation lines and pins	$700
Fertilizer	$300
Hortonova Netting	$300
Office Supplies	$200
Peat/Vermiculite/Perlite	$900
PermaTill for vole prevention	$300
Pest Control	$300
Product selling supplies	$200
Seed starting supplies	$200
Shipping boxes, packing, labels	$600
Supplies, shears, gloves, organza bags	$700
State Licenses and taxes	$300
Website and subscriptions	$600

 

Best Practices for Virus Management

Educate yourself about dahlia viruses and their symptoms, such as stunted growth, yellowing veins, and necrotic spotting.  Remove and dispose of weak or sick plants—do not compost them.  Always disinfect tools between plants.  With dahlias being asymptomatic, they may not show any signs of virus as the virus level is low and the dahlia is able to fight back.  It may be low enough that insects cannot pick it up.  However, the virus is carried through the tuber, so it is important to disinfect your tools.  Once the virus show symptoms, the virus load is high.  Thrips and aphids can spread the virus on more dahlias, so it is important to inspect your dahlias often.  This is best to do on a cloudy day as the symptoms on the leaves will stand out more in the shade than in the sun.  Remove any odd looking plants.

The American Dahlia Society recommends planting untested dahlias in one area and first-year seedlings or tested plants elsewhere, maintaining as much separation as possible.  Implement early, consistent thrip and aphid control strategies and disinfect tools with a 10% bleach solution between plants.

Having virus-free stock requires effort and ongoing management.  Even when you purchase virus-free cuttings, they can become infected if exposed to virus-carrying thrips from neighboring dahlias or other plants, so continued vigilance is crucial.  Continue learning and adapting virus management strategies to keep your dahlia garden as healthy as possible.

Key Takeaways

• Regularly inspect and cull unhealthy dahlias.
• Disinfect tools frequently with bleach or Virkon S.
• Separate named dahlia cultivars from seedlings to minimize cross-infection.
• Implement seasonal virus testing, especially for plants intended for propagation.
• Monitor and control thrips and aphids to limit virus spread.
• Maintain good weed and garden hygiene to reduce pest habitats.

My Approach to Maintaining a Healthy Dahlia Garden

Commitment to Cleanliness and Plant Health

I am dedicated to keeping my dahlia garden as healthy and virus-free as possible.   To achieve this, I consistently remove any plants that appear weak or sick, ensuring that only vigorous, healthy specimens remain in the garden.   Regular culling of compromised plants helps prevent the potential spread of viruses and other diseases.

Tool Disinfection Practices

Another critical step in my routine is the disinfection of all gardening tools.   By thoroughly cleaning and disinfecting tools after use, I reduce the risk of unintentionally transferring viruses or pathogens between plants.

Separation of Cultivars and Seedlings

I maintain a clear separation between my named dahlia cultivars and my own seedlings.   This practice helps limit cross-contamination and allows for more effective monitoring and management of plant health within each group.

Seasonal Virus Testing

In the fall, I conduct targeted virus testing on dahlia seedlings that I intend to propagate through cuttings in the following season.   This additional step enables me to identify and remove any plants that may carry viruses before they can be spread further, especially during the propagation process.

Commitment to Consistency and Transparency

Through the consistent implementation of these practices—culling unhealthy plants, disinfecting tools, separating cultivars from seedlings, and conducting fall virus testing—I am actively working to reduce the spread of viruses in my dahlia garden.   Given the prevalence of viruses among many flower cultivars, I cannot guarantee that all my dahlia tubers are entirely virus-free.   However, I am committed to ongoing virus management and to doing my best to provide healthy, robust dahlias.

Paula