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Understanding Dahlia Diseases & Dahlia Viruses

What You Need to Know About Viruses and Diseases Affecting Your Dahlias

Growing beautiful dahlias in your garden can bring immense joy, but unfortunately, these stunning cut flowers are not immune to diseases and viruses. No matter how careful you are in the garden, if you grow dahlias long enough, you will eventually come across a dahlia plant with disease or virus. In this comprehensive guide to the most common dahlia diseases, we’ll explore the common diseases and viruses that can afflict your dahlia plants, how to identify them, and the preventive measures and treatments you can take to protect your precious flowers. 

beautiful dahlias growing in the garden

Important Note/Disclosure: This blog post is intended to provide general information and suggestions for disease and pest management of growing dahlias. For specific diagnosis and treatment advice please consult with a local horticulturist or plant disease specialist.

Table Of Contents
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How Dahlia Diseases & Viruses Are Spread

Dahlia viruses can be spread through various means, and understanding their modes of transmission is crucial for preventing their spread. Here are some of the common ways in which dahlia viruses can be transmitted:

dahlia virus on leaves

Aphids, Thrips and Other Insect Vectors:

Aphids, small sap-sucking insects, are notorious carriers of dahlia viruses. They feed on infected plants and can pick up viral particles, subsequently transmitting them to healthy plants as they move and feed. Other insect vectors, such as thrips and whiteflies, can also contribute to virus transmission. Thrips, a big dahlia pest, love dahlias (especially white dahlias I’ve found) and they are believed to be one of the worst vectors for transmitting disease from one plant to the next. Unfortunately insects can travel from one garden to the next so having a good integrated pest management system is crucial to controlling and managing dahlia disease. Learning to control aphids and other “bad bugs” in your garden can definitely help to cut down on the transmission of disease.

Infected Dahlia Tubers Used For Dahlia Cuttings:

Dahlia viruses can also be transmitted during the process of taking cuttings of infected plant material. When infected plant tissues are used for propagation, the resulting plants will carry the virus. Garden tools should always be cleaned and sanitized between plants to spread contamination from diseased plants.

propagating dahlias

Contaminated Tools and Equipment:

Shared gardening tools and equipment, if contaminated with viral particles, can inadvertently spread dahlia viruses from one plant to another. It is essential to clean and disinfect tools after each use, especially when working with infected plants. It is recommended to sanitize your tools between each and every dahlia plant.

Below you will find a video showing how I disinfect my tools while working in the garden.

Seed Transmission:

While dahlia seeds themselves have a low risk of carrying some viruses, if the parent plants used to produce the seeds are infected, there is a possibility of viral transmission through the seeds. However, this mode of transmission is less common compared to vegetative propagation methods. It is believed that DNA viruses like Dahlia Mosaic can be carried over to the seeds. For this reason, it is best to only collect dahlia seeds from healthy dahlia plants.

dahlia seedlings are usually virus free
always use clean garden tools

Contaminated Soil:

It is believed that some bacteria (like gall) can persist at the soil level for extended periods of time. If dahlias are planted in soil where infected plants were previously grown, the bacteria can infect the new plants through their roots or open wounds. Proper crop rotation and sanitation practices can help reduce the risk of soil-borne transmission. This is especially true for leafy gall and crown gall. If you remove a plant infected with either of these diseases, it’s recommended that you do not plant again in that spot in the same season. Some gardeners and researchers also suggest waiting an entire year before planting dahlia tubers (or any plant) in the same spot where you had the plant problem. When removing any diseased plants, it’s important to throw them away and not compost them as soil-borne fungus can spread through your compost and infect other plants.

healthy soil

Natural Dispersal:

Under certain conditions, some bacterial fungus like powdery mildew can spread naturally within a garden or landscape. This can occur through wet weather, wind, rain, or the movement of infected plant debris.

Controlling weeds and removing infected plant material promptly can help limit natural dispersal. High humidity and wet conditions in the garden can also contribute to the spread of fungal diseases like powdery mildew.

By having a better understanding of the various modes of transmission, gardeners can implement appropriate measures to prevent the spread of dahlia viruses. Regular inspection of plants, early detection of infected plants, practicing good sanitation, and implementing integrated pest management strategies can significantly reduce the risk of transmission among dahlia plants, helping to maintain a healthy and vibrant garden.

How To Tell If Your Dahlia Plant Has A Virus Or Nutrient Deficiency

Determining whether a dahlia plant is affected by a virus or experiencing a nutrient deficiency can sometimes be challenging, as certain symptoms may overlap. When faced with unusual leaf patterns, stunted growth, or other abnormalities, it’s important to carefully evaluate the situation. Nutrient deficiencies in a dahlia plant or in your soil can cause discoloration, distorted growth, or specific symptoms associated with particular nutrients. Garden pests such as thrips and leaf hoppers can also cause stunted growth or disfigured leaves. Conducting a soil test to assess nutrient levels and adjusting fertilization accordingly can help rule out nutrient deficiencies. It is strongly recommended to do a soil test prior to your growing season. However, it’s never too late to do a soil test. You can always use the test results to improve your soil for next year.

This is one of the best videos I have seen showing dahlia nutrient disorders

There Is No Cure For Dahlia Virus

Unlike nutrient deficiencies, viral infections often result in mosaic patterns, mottling, or yellowing of leaves, and these symptoms tend to appear more randomly across the plant. Dahlia viruses cannot be cured, and affected plants should be removed promptly to prevent further spread. Do not put infected plants in your compost, instead you will want to dispose of them in the trash to prevent the spread of disease. If you’re uncertain about the cause of the symptoms, consulting with a local horticulturist, plant pathologist, or agricultural extension service can provide valuable guidance in diagnosing the issue and taking appropriate action. Of course, I personally follow the advice of The American Dahlia Society and follow the simple guideline, “if in doubt, throw it out.” It’s not worth possibly infecting other healthy plants in your garden.

Signs Your Dahlia Plant Might Have a Virus or Disease

dahlia leaf showing signs of a virus

Dahlias, just like any other plants, can exhibit specific signs when afflicted by diseases or viruses. It’s important to note that not all virused or diseased dahlias will show systems. Many plants may carry a virus and be asymptomatic. To help you better spot any virus in your garden, keep an eye out for the following symptoms:

  1. Stunted Growth: If your dahlia plants aren’t growing as vigorously as expected or appear stunted, it could be a sign of disease or virus.
  2. Discoloration: Look for unusual discoloration on the leaf surface, such as ring spot, yellow spots, brown spots, bronzing, or mottling.
  3. Distorted Growth: Distorted or twisted leaves, stems, or flowers may indicate the presence of a viral infection.
  4. Necrotic Lesions: Dark, dead patches or lesions on leaves, stems, or flower buds may signify a disease affecting your dahlias.

Understanding Different Dahlia Viruses

Dahlia plants can fall victim to various viruses, each with its own characteristics and effects on plant health. Many dahlia viruses can have relatively similar symptoms and it can sometimes be tough to know which virus or disease is present. Please note that there is no cure for any of these diseases so if you find an infected plant in your garden you will need to properly dispose of it and thoroughly disinfect your tools. Let’s explore a few of the most common dahlia viruses:

Impatiens Necrotic Spot Virus (INSV):

Impatiens Necrotic Spot Virus can affect dahlias. It causes ring spots, necrotic lesions, and distorted growth in infected plants. This virus is primarily transmitted through thrips, so controlling thrip populations is crucial. It is believed that this virus is less common in dahlias than other dahlia viruses.

Million Moments, CC BY-SA 3.0 http://creativecommons.org/licenses/by-sa/3.0/, via Wikimedia Commons

Tomato Spotted Wilt Virus (TSWV):

Tomato Spotted Wilt Virus is another viral pathogen that can infect dahlias. Look for symptoms such as yellowing, bronzing, and necrotic streaks on leaves. Thrips serve as carriers for this virus, so effective thrip management is essential. 

Tobacco Streak Virus (TSV):

Dahlia plants can also be affected by Tobacco Streak Virus, leading to mosaic patterns, leaf distortion, and stunted growth. This virus is commonly transmitted by aphids and thrips, so it is important to taking preventive measures against these garden pests.

Dahlia Mosaic Virus (DMV) and Dahlia Common Mosaic Virus (DCMV):

Both Dahlia Mosaic Virus and Dahlia Common Mosaic Virus are specific viral diseases that frequently target dahlias. They cause mosaic patterns, chlorophyll loss, leaf distortion, and reduced flower quality. Aphids are common vectors for these viruses, so controlling aphid populations is crucial for prevention.

dahlia virus on leaves
This dahlia plant is believed to be infected with DMV (Dahlia Mosaic Virus) as you can see through the chlorophyll loss and leaf distortion.

Cucumber Mosaic Virus (CMV):

Cucumber Mosaic Virus is commonly spread by aphids. Infected plants can have stunted growth, malformed leaves, yellowing, and ring spots. This virus is not specific to dahlias and can affect thousands of different plants in your garden.

Anette Phibbs, WI Department of Agriculture, Trade & Consumer Protection, Bugwood.org, CC BY-SA 3.0 https://creativecommons.org/licenses/by-sa/3.0, via Wikimedia Commons

Types of Diseases in Dahlias

Apart from dahlia viruses, several diseases can also affect your dahlia plants. Let’s explore a few of the most serious diseases of dahlias:

Crown Gall:

Crown Gall is a highly contagious bacterial disease characterized by swollen, distorted growths near the base of the stem. This disease causes tumors to form on your dahlia and will eventually prevent it from forming new growth. Avoid planting dahlias in areas with a history of Crown Gall, as it can persist in the soil. If you find a dahlia tuber infected with crown gall, best practice is to also remove the soil that was surrounding the infected plant. Do not try to cut off the visibly diseased portion as the entire plant is infected and needs to be disposed of properly.

Leafy Gall:

Leafy Gall is another bacterial disease specific to dahlias. It causes shoot proliferation where many new shoots are fused together at the base of the plant. Remove and destroy infected plants to prevent further spread as there is currently no cure for leafy gall.

Dahlia Smut:

Smut is a fungal disease that affects dahlias, causing black, powdery masses on leaves, stems, and flowers. Prompt removal and destruction of infected plant parts are essential for control.

Powdery Mildew

Powdery Mildew is a common fungal disease affecting many plants, including dahlias. Look for a white, powdery coating on leaves, stems, and flowers. Fungicidal treatments and good airflow can help manage this disease. To prevent late season powdery mildew, it is recommended that you strip the lower leaves on your dahlias to allow for proper air flow.

Bacterial Stem Rot:

Stem Rot is a fungal disease that causes rotting of stems, leading to wilting and eventual collapse of the plant. Avoid overwatering and ensure proper drainage to prevent this disease.

Bacterial Stem Rot on kale plant. Photo from Scot Nelson, CC0, via Wikimedia Commons
Is It Crown Gall or Leafy Gall?

Wondering is it Crown Gall or Leafy Gall? Check out this great pdf from Oregon State University. Click here to read this publication written by Melodie Putnam and Marilyn Miller.

Verticillium Wilt: A Threat to Dahlia Plants

In addition to viruses and other diseases, dahlias are susceptible to Verticillium wilt, a fungal disease caused by the soilborne pathogen Verticillium dahliae. Here’s what you need to know about this threat to your dahlia plants:

Howard F. Schwartz, Colorado State University, Bugwood.org, CC BY 3.0 , via Wikimedia Commons

Understanding Verticillium Wilt:

Verticillium wilt affects a wide range of plants, including dahlias. The fungus invades the plant’s vascular system, disrupting water and nutrient transport, leading to wilting and decline.

Recognizing Symptoms of Verticillium Wilt

Symptoms of Verticillium wilt in dahlias include wilting and yellowing of leaves, often starting on one side of the plant. Over time, the wilting may progress to entire branches or the entire plant. In some cases, brown discoloration can be observed in the vascular tissue when stems are cut open.

Soilborne Persistence:

Verticillium dahliae can persist in the soil for several years, making it a challenging disease to manage. The fungus survives in plant debris and can infect dahlias and other susceptible plants in the same area.

Preventive Measures:

To reduce the risk of Verticillium wilt in your dahlia garden, consider the following preventive measures:

Crop Rotation:

Avoid planting dahlias or other susceptible plants in the same area for consecutive years. Rotate with non-host plants to reduce the pathogen’s population in the soil.

Resistant Varieties:

Some dahlia varieties exhibit tolerance or resistance to Verticillium wilt. When selecting new dahlias, look for varieties labeled as resistant to this disease.

Soil Solarization:

Solarization is a technique that utilizes the sun’s heat to kill soilborne pathogens. Before planting, cover the soil with clear plastic during the hottest months of summer to raise soil temperatures and eliminate or reduce the Verticillium population.

Sanitation Practices:

Remove and destroy infected plant debris to prevent the spread of the pathogen. Clean and disinfect garden tools and equipment to avoid transferring the fungus to healthy plants.

Healthy Soil and Plants:

Maintain overall plant health through proper watering, fertilization, and balanced soil conditions. Healthy plants are better equipped to resist and recover from diseases.

Verticillium wilt can be a persistent challenge in dahlia gardens, but with careful management and preventive practices, you can minimize its impact on your plants.

Note: If you suspect Verticillium wilt in your dahlias, consult with a local plant pathologist or horticulture expert for a proper diagnosis and guidance on control strategies tailored to your specific situation.

By being aware of the signs and taking proactive measures, you can help protect your dahlias from the devastating effects of Verticillium wilt and maintain their health and vitality for years to come.

Pictures of Dahlias Infected with Various Diseases and Viruses

To help you visually identify diseases and viruses in your dahlia plants, here are some pictures showcasing infected dahlias:

R1 #37 #21-52 DEA7 IMG_0884 0726 r2
Click on the photo above to view the Flickr gallery of virused dahlia by Linda Taylor https://www.flickr.com/photos/141837887@N08

What to Do If Your Dahlia Plant Has a Disease or Virus

If you suspect that your dahlia plant is affected by a disease or virus, it’s important to take immediate action. Dahlia diseases and viruses are on the rise and together we can help reduce the spread. Please follow these steps to prevent further spread of disease:

  1. Remove and Destroy: Carefully remove and destroy and infected plants to prevent the disease or virus from spreading to healthy plants. Burn or dispose of them in sealed bags, do not compost infected plants.
  2. Isolate: If you have multiple dahlia plants, isolate the infected plant to prevent transmission to others. Maintain strict hygiene by washing hands and tools thoroughly after handling infected plants.
  3. Monitor and Treat: Keep a close eye on your remaining dahlia plants for any signs of disease or virus. If detected early, some viral infections may benefit from treatment with antiviral agents. Fungal or bacterial diseases like powdery mildew can often be managed with appropriate fungicides or bactericides.
  4. Sanitize: Clean and disinfect your gardening tools, pots, and equipment after handling infected plants. This helps prevent the transfer of pathogens to healthy plants during future use.
    1. The American Dahlia Society recommends 3 different proven methods for disinfecting and sanitizing tools between each plant:
      1. 10% bleach solution in water 
      2. 4 tsps of Dawn Dishwashing Detergent to 5 cups of water
      3. Virkon S (commercial veterinarian disinfectant and virucide)

Testing for Dahlia Viruses

If you suspect your dahlia plants are infected with viruses, it’s important to confirm the presence of the virus for accurate diagnosis and appropriate action. While laboratory testing is the most reliable method, there are a few options available for testing:

Agdia virus testing
This plant sample tested positive for TSV using an Agdia Home Test Kit

ELISA (Enzyme-Linked Immunosorbent Assay):

ELISA is a common laboratory test used to detect specific viral antigens in plant tissues. You can send a sample from an infected dahlia plant to a specialized plant diagnostic laboratory for ELISA testing. Contact your local agricultural extension office for information on laboratories offering this service. Note: this option can be expensive and most home gardeners most option choose to just follow the American Dahlia Society’s advice of “If in doubt, throw it out.”

PCR (Polymerase Chain Reaction):

PCR is a molecular technique used to amplify specific viral DNA or RNA sequences. It provides highly accurate results. However, PCR testing is more specialized and may require assistance from a plant diagnostic laboratory or plant pathologist. This option also can be an expensive option to diagnosis disease and/or virus.

Home Test Kits:

Some home test kits are available for detecting certain viruses in plants. These kits often use antibody-based methods similar to ELISA but in a simplified format. They may be useful for preliminary screening but may not provide as accurate results as laboratory testing. Follow the instructions provided with the kit for sample collection and testing.

Remember, lab testing offers the most accurate and reliable results, but it is not always an affordable option. Always consult with a plant diagnostic laboratory or expert to determine the best testing method for your situation. If you do decide to test, you’ll have a clearer understanding of the specific viruses affecting your dahlia plants. This information can guide your decisions regarding plant removal, treatment, and prevention strategies.

***Note: Testing for viruses may incur a fee, and the availability of testing methods may vary depending on your location.

Persistence of Dahlia Diseases in Soil

Dahlia diseases and viruses can persist in the soil, posing a threat to future dahlia plantings. Here’s what you need to know:

  1. Crop Rotation: Practice crop rotation by avoiding planting dahlias in the same location each year. This helps disrupt the life cycle of pathogens and reduces the risk of disease.
  2. Soil Solarization: Consider solarizing the soil in affected areas by covering it with clear plastic during the hot summer months. This technique helps to eliminate soil-borne pathogens. *Note, this option is usually not viable for backyard gardeners or those growing in small spaces.

Tips for Preventing Diseases in Dahlia Plants

Prevention is key when it comes to preventing diseases in dahlia plants. By implementing these proactive measures, you can significantly reduce the risk of infections and help keep your dahlias healthy:

Buy quality tubers from reputable growers:

Start with healthy tubers from trusted sources. In the United States, buy dahlia tubers from growers who are licensed and inspected by their Department of Agriculture. It’s ok to ask if growers have a practice for culling for disease (many will list this on their website). Inspect tubers for any signs of disease or damage before planting. Healthy tubers have a better chance of producing disease-resistant and vigorous plants.

buy quality dahlia tubers

Clean and disinfect tools:

Before working with your dahlia plants, clean your gardening tools and equipment. Disinfect your tools between each plant. This prevents the spread of pathogens from one plant to another.

clean garden tools

Keep up with garden pests:

Pests can weaken plants and make them more susceptible to diseases. Implement integrated pest management (IPM) practices to control pests effectively. This may include physical barriers, traps, biological controls (like beneficial insects), or targeted pesticide use if necessary.

Inspect plants on a regular basis:

Regularly check your dahlia plants for any signs of diseases, pests, or abnormalities. Early detection allows for timely intervention and reduces the chances of diseases spreading. Remove any infected plant parts promptly.

Maintain proper plant spacing:

Adequate spacing between dahlia plants improves air circulation and reduces humidity around the foliage. This minimizes the risk of fungal diseases such as powdery mildew and allows the leaves to dry quickly after rainfall or watering. Dahlias need good air circulation to prevent fungal infections like powdery mildew.

Provide good drainage:

Ensure that your dahlia beds have well-draining soil. Excessive moisture can create a favorable environment for root diseases. Consider amending the soil with organic matter or raised bed gardening to improve drainage.

Avoid overhead watering:

Water the base of the plants rather than spraying water directly on the foliage. Overhead watering can lead to prolonged leaf wetness, making the plants more susceptible to diseases. Use drip irrigation or a soaker hose to deliver water directly to the soil.

Here a drip line is providing irrigation to the plants.

Promote plant health:

Maintain optimal growing conditions for your dahlias. Provide sufficient sunlight, proper nutrition through balanced fertilization, and regular watering. Healthy plants are better equipped to resist diseases and recover quickly if they do become infected.

Practice good sanitation:

Clean up fallen leaves, plant debris, and weeds from your dahlia garden regularly, these all provide habitats for pests. Remove any diseased plant parts and dispose of them properly. This reduces the sources of infection and prevents the buildup of pathogens in the garden.

Rotate crops:

Avoid planting dahlias or other susceptible plants in the same location year after year. Practice crop rotation by planting unrelated plant species in the same spot. This helps break the disease cycle and reduces the buildup of pathogens in the soil.

By following these preventive measures, you can create a healthier environment for your dahlia plants and minimize the occurrence of diseases. Remember, a proactive approach goes a long way in protecting the beauty and longevity of your garden.

Note: While these tips can significantly reduce the risk of diseases, it’s important to monitor your plants closely and seek professional advice if you suspect any serious issues.

Common Dahlia Pests: Potential Disease Spreaders

While diseases can directly affect dahlia plants, it’s important to be aware of the role pests can play in their transmission. Some pests act as carriers or vectors, spreading diseases from plant to plant. Here are the most common dahlia pests that can contribute to disease spread:


These small, soft-bodied insects feed on the sap of dahlia plants. They can transmit viral diseases such as mosaic viruses and impatiens necrotic spot virus (INSV). Aphids reproduce quickly, so early detection and control are essential.

aphids attacking plant


Thrips are tiny, slender insects that can cause significant damage to dahlia plants. They feed by piercing the plant tissues and sucking out the sap. Thrips can transmit tomato spotted wilt virus (TSWV) along with other viruses, which can cause severe damage to dahlias and other ornamental plants.

close up of thrips on leaf


These tiny, winged insects congregate on the undersides of leaves, sucking plant sap. Whiteflies can transmit viral diseases such as tobacco streak virus (TSV). They also excrete honeydew, which promotes the growth of sooty mold, further compromising plant health.

whitefly on the underside of a plant leaf

Spider Mites:

Spider mites are minuscule pests that feed on plant tissues, causing discoloration and stippling on leaves. Their feeding weakens the plants and makes them more susceptible to diseases. Severe infestations can lead to webbing and further damage.

spider mite infestation

Snails and Slugs:

These mollusks are primarily a concern for young dahlia plants. They feed on leaves, stems, and flowers, leaving behind irregular holes and slime trails. Snails and slugs can indirectly contribute to disease transmission by creating entry points for pathogens.

slug in garden


Nematodes are microscopic roundworms that live in the soil. Some species can cause damage to dahlia roots, weakening the plants and making them more susceptible to diseases. Root-knot nematodes are a common concern in many gardens. Please note that not all nematodes are bad, there are many beneficial nematodes that you can release in the late spring or early fall to help with your integrated pest management (IPM) strategy.

To prevent the spread of diseases by these pests, consider the following measures:

  • Regular monitoring: Regularly inspect your dahlia plants for signs of pest infestations. Early detection allows for timely intervention and reduces the risk of disease transmission.
  • Integrated pest management (IPM): Implement an IPM approach that combines cultural, mechanical, and biological control methods. This may include physical barriers, sticky traps, beneficial insects, and targeted pesticide use if necessary.
  • Good sanitation: Keep your garden free from weeds, fallen leaves, and debris that can harbor pests and diseases. Remove any infected plant material promptly and dispose of it properly.
  • Encourage beneficial insects: Attract beneficial insects such as ladybugs, lacewings, and parasitic wasps to your garden. These natural predators help control pest populations and minimize disease spread.
  • Proper watering: Avoid overwatering, as it can create conditions favorable for pest development. Water the base of the plants and use drip irrigation or soaker hoses to minimize leaf wetness.
  • Crop rotation: Practice crop rotation by avoiding planting dahlias or other susceptible plants in the same area for consecutive years. This disrupts pest and disease cycles, reducing the chances of re-infestation.

By being vigilant about pest management, you can reduce the risk of disease transmission and maintain healthier dahlia plants. Combining preventive measures, regular monitoring, and targeted interventions will help protect your dahlias from both pests and the diseases they can spread.

Harnessing the Power of Beneficial Insects for Disease Prevention

In your quest to protect your dahlia plants from diseases and viruses, don’t overlook the valuable role of beneficial insects. These tiny allies play a significant role in controlling pest populations and can help prevent the spread of diseases. Here’s why they are essential:

beneficial insects can play a large role in helping to prevent the spread of disease and virus in the garden
  1. Natural Pest Control: Beneficial insects, such as ladybugs, lacewings, and minute pirate bugs, are natural predators of common garden pests like aphids, thrips, and mites. By preying on these pests, they help keep their populations in check, reducing the risk of disease transmission. To learn more about how to keep your garden pest free without using pesticides, click here.
  2. Pollination and Plant Health: Many beneficial insects, including bees and butterflies, are important pollinators. Their visits to dahlia flowers aid in pollination, resulting in better fruit set and overall plant health. Strong, healthy plants are more resilient to diseases and better equipped to fend off pathogens.
  3. Insect Interference: Some beneficial insects, such as parasitic wasps, can directly interfere with disease transmission by attacking and parasitizing pest insects that serve as disease vectors. By targeting and eliminating these vectors, they break the disease cycle and reduce the spread of pathogens.
  4. Cultural Control Support: Beneficial insects complement cultural control practices, such as maintaining proper plant spacing, removing infected plant material, and practicing good sanitation. They provide an additional layer of defense by actively reducing pest populations that could otherwise transmit diseases.

Horticultural Sprays for Dahlia Disease Prevention

You may find that chemical controls are necessary for combating disease spreading insects in your garden or extreme cases of powdery mildew. I personally have not used any chemical or horticultural oil sprays in my garden for the past three years now, but horticultural sprays can be valuable tools for some. These sprays, often available in both chemical and organic formulations, serve various purposes in disease prevention and management:

  1. Fungicidal Sprays: Fungicidal sprays are designed to combat fungal diseases such as powdery mildew, and stem rot. When applied preventatively or at the first signs of fungal growth, they can effectively halt the progression of these diseases. Be sure to follow the product label instructions for proper application.
  2. Insecticidal Sprays: While primarily aimed at controlling garden pests, certain insecticidal sprays can indirectly assist in disease prevention. By reducing pest populations like aphids, thrips, and whiteflies, these sprays lower the risk of pests acting as disease vectors. Please note that many insecticidal sprays can also harm beneficial insects like ladybugs and bumble bees. 
  3. Anti-Viral Sprays: Some horticultural sprays are specifically formulated to combat viral diseases in plants. These sprays may not cure existing infections but can be used to prevent further viral spread when used as a preventive measure.

Before using any horticultural or anti-fungal spray, it’s crucial to:

  • Identify the Disease: Properly diagnose the disease affecting your dahlias. Using the right spray for the specific pathogen is essential for effective control.
  • Read Labels: Thoroughly read and follow the label instructions on the chosen spray product. This includes information on application timing, rates, and safety precautions.
  • Consider Environmental Impact: Be mindful of the potential environmental impact of chemical sprays. Organic and environmentally friendly options may be preferred for eco-conscious gardeners.
  • Apply Preventatively: In many cases, preventive application before the disease strikes is more effective than trying to control a full-blown outbreak. Consult with experts or local garden centers for advice on timing.
  • Rotate Products: To reduce the risk of resistance development in pathogens, consider rotating between different horticultural sprays with different active ingredients.
  • Personal Safety: Wear appropriate protective gear when handling and applying sprays, especially chemical-based products. Safety should always be a priority.

Remember that horticultural sprays may be a part of an integrated disease management strategy, along with good garden hygiene, proper plant spacing, and vigilant monitoring. Consult with local horticultural experts or extension services for guidance on choosing the right sprays and using them effectively in your dahlia garden.

Dahlia Seeds and Virus Transmission

close up of dahlia seeds

Dahlia seeds generally have a low risk of carrying viruses compared to infected plant tissues. Obtaining seeds from reputable sources reduces the likelihood of virus transmission. While seeds themselves are typically free from viruses, it’s important to remain vigilant during the propagation process. Regular visual inspection and prompt removal of infected plants are necessary. For those prioritizing virus-free plants, obtaining tubers or cuttings from dahlia growers who test for virus and cull is recommended. Overall, the risk of dahlia seeds carrying viruses is low, but maintaining good hygiene and disease management practices during propagation is still essential.

If In Doubt, Throw It Out

Did you know that the American Dahlia Society strongly emphasizes the importance of promptly removing dahlia plants that are suspected to be infected with viruses or diseases? Their recommendation, “if in doubt, throw it out,” reflects the need to prioritize the overall health of the garden and prevent the spread of potential pathogens. By removing infected plants, you can help to safeguard the remaining dahlia collection and prevent further contamination. By taking swift action and responsibly discarding infected plants, gardeners contribute to maintaining a vibrant and disease-free dahlia garden, allowing the healthy plants to thrive and continue providing beauty for seasons to come.

if in doubt, throw it out.

More Resources for Dahlia Disease

For more in-depth information and resources on dahlia diseases and viruses, consider referring to the following reputable sources:

  1. American Dahlia Society:  The American Dahlias Society is organized to promote and encourage the development of and appreciation of the dahlia through educational and research activities and by supporting the local dahlia societies. https://www.dahlia.org/
  2. Be Part of The Solution | Dahlia Virus Guide from WSU and The American Dahlia Society: https://dahlia.org/wp-content/virusdocs/vdoc%2019%201.pdf
  3. “Virus in Dahlias by Dr. Hanu Pappu of Washington State University” https://www.youtube.com/watch?v=UrvnptVmIOU
  4. Oregon State University & Pacific Northwest Pest Management Handbooks: http://pnwhandbooks.stage.extension.oregonstate.edu/plantdisease/host-disease/dahlia-virus-diseases
  5. Agdia: Agdia leading provider for disease testing with plant tissue. https://www.agdia.com/

***Important Note/Disclosure: This blog post is intended to provide general information and suggestions for disease and pest management of growing dahlias. For specific diagnosis and treatment advice please consult with a local horticulturist or plant disease specialist.***

Remember, early detection and proper pest & disease management are key to minimizing the impact of diseases and viruses on your dahlia garden. Unfortunately dahlia diseases and viruses are common, but by staying vigilant, implementing preventive measures, and taking prompt action if disease or virus symptoms arise, you can protect your beloved dahlias and enjoy their beautiful blooms for years to come. 

Happy gardening!

The Flowering Farmhouse Signature

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  1. This was a really good article and I shared it in the Dahlia Growers FB group in a comment. I have individual nectrotic spots on 3 Pam Howden plants, and I’m not sure what it is. I”m sure they have to come out of the ground, unfortunately. Thanks for a well put together article, and there’s an annoying pop up video that keeps interfering with writing this comment….

    1. Thank you Jess for taking the time to leave a comment. Do you think the spots could be a fungus like dahlia smut? I appreciate you sharing on Dahlia Growers! I’ve spent the last two years working on this post doing tons of research 😉

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