Common Dahlia Viruses and What They Do

Dahlias are beloved for their vibrant colors, dramatic blooms, and incredible diversity. However, they are also susceptible to a number of plant viruses that can quietly weaken growth and diminish performance. These viruses often spread through insects, tools, and traditional tuber division, making them hard to detect and easy to pass along. Understanding the most common dahlia viruses and what they do, helps gardeners recognize why starting with virus-indexed plants is so important.

5 Main Types of Virus in Dahlia

Dahlias are vulnerable to several plant viruses, each affecting growth, bloom quality, and long-term vigor in different ways. While some viruses cause dramatic, unmistakable symptoms, others remain hidden for seasons before reducing performance. The five major virus groups below—both RNA and DNA types—represent the most common and most impactful threats to dahlias. Understanding how each one behaves will help gardeners recognize issues early and appreciate the value of starting with clean, virus-indexed plants.

Tomato Spotted Wilt Virus (TSWV)

Photo by Linda Taylor

What it is: Produces strong symptoms in plants and persists over winter in tubers. Spreads rapidly in garden. Plants showing symptoms should be destroyed.

How it affects plants:

Causes bronze or black streaks on foliage
Leads to ring spots, mottling, or distorted growth
Produces small, twisted, or malformed blooms
Weakens the plant’s overall ability to perform and overwinter

TSWV is especially concerning because thrips can spread it even with brief feeding periods.

Tobacco Streak Virus (TSV)

Photo by Linda Tayler

What it is: A virus present in many crops and ornamentals, often transmitted through thrips or contaminated pollen. Very problematic. Survives winter storage. Plants showing symptoms should be destroyed.

How it affects plants:

Causes streaking or yellowing in leaves
Leads to malformed or incomplete blooms
Reduces stem strength and flower size
Can compromise tuber development and storage quality

TSV has subtle symptoms early on, making it easy to overlook—but its long-term effects are significant.

Impatience Necrotic Spot Virus (INSV)

Photo by Linda Tayler

What it is: A virus spread by thrips, common in both greenhouses and outdoor gardens.
How it affects plants:

Creates brown, necrotic (dead) patches on leaves
Leads to stem streaking and uneven growth
Reduces plant vigor and bloom production
Severely affects plant form and longevity

Cucumber Mosaic Virus (CMV)

Photo by Linda Tayler

What it is: A common virus affecting many ornamentals and vegetables, transmitted mainly by aphids.
How it affects plants:

Produces yellowing, ring spots, or mosaic patterns on leaves
Can lead to stunted plants and reduced flowering
Causes irregular or poorly formed blooms
Can severely impact vase life and color vibrancy

CMV spreads rapidly in gardens with heavy insect pressure and can cause serious performance decline when present in dahlias.

Dahlia Mosaic Virus (DMV) & Dahlia Common Mosaic Virus (DCMV)

Photo by Linda Tayler

What it is: The most widely recognized dahlia virus group, often referred to as the “Dahlia Mosaic Virus complex.” DCMV is considered a variant of DMV so they are treated as one in the same. Widespread problem.

How it affects plants:

Causes yellow mottling, mosaic patterns, or chlorotic (lightened) patches on leaves
Can lead to distorted foliage and weaker stems
Reduces plant vigor and bloom quantity
Infected tubers may store poorly and decline faster over time

DMV is persistent and easily spread through vegetative propagation. Symptoms can vary significantly among varieties, making it difficult to identify without testing.

Why These Dahlia Viruses Matter

Although symptoms vary, all common dahlia viruses share one trait:
They reduce the health, beauty, and long-term performance of the plant.

Infected dahlias may display:

Reduced vigor and weaker stems
Smaller, fewer, or misshapen blooms
Poor color clarity
Lower vase life in cut-flower arrangements
Less reliable tuber storage and overwintering success
Decline over successive growing seasons
Color breaks in blooms

Because dahlias are vegetatively propagated, viral infections are easily passed from one generation to the next—unless plants are actively tested and cleaned through tissue culture.

Quick Facts About Dahlia Viruses

Plants with any of the common viruses may not show symptoms of the virus.
Asymptomatic plants in your garden may become symptomatic when grown in another garden. Stress and other environmental factors can trigger expression. Epigenetics.
Viruses do not always exist throughout the whole plant. This can make testing tricky. Some plants could give false negatives test results. For this reason, leaf samples should be taken from three different parts of the plant for testing.
RNA and DNA viruses are not transmitted to seedlings even when both parents test positive.
RNA viruses have multiple plant hosts.
Dahlia is the only known host for DMV/DCMV.

Photo by Linda Tayler

Dahlia Virus Transmission Facts

Thrips are the main insect vector of the RNA viruses. Larval stages pick up the virus from infected plant. The virus then moves throughout the life cycle of the insect. Adults can transmit but cannot pick up the virus.
Aphids are the insect vector of DNA viruses. DMV/DCMV
Cutting and pruning tools not disinfected between individual plants

Learn more about how to keep your dahlias virus-free in the gardern.

The Good News: Virus-Indexed Plants Break the Cycle

Spring Hill Nursery’s virus-indexed dahlias are tested for all major viruses—CMV, DMV & DCMV, INSV, TSV, and TSWV—to ensure you begin with truly clean stock. When viruses are removed from the equation, dahlias grow with superior vigor, produce larger and more consistent blooms, deliver better vase life, and develop healthier, stronger tubers that store reliably.

Starting with virus-free genetics gives gardeners the best possible foundation for vibrant, high-performing dahlias that shine season after season. For more information on dahlia virus, visit the American Dahlia Society.