Our Common Sense Dahlia Virus Protocol

Our Common Sense Dahlia Virus Protocol

Dahlias, like most living things, are susceptible to viruses. They do not have the ability to clear a virus, unlike humans. Once a dahlia is infected by a virus it remains in the tissue. There is no cure. Some dahlias appear to be able to resist displaying viral symptoms despite being infected. In most dahlias, viral infection is not fatal. The plant will likely continue to grow and bloom.

The primary way dahlia virus is spread is through insects. Specifically, insects with piercing, sucking mouth parts such as thrips and aphids. The viruses that infect dahlias can also be found in thousands of other plant species. Therefore inter-species transmission of viruses via insects is possible and common. An insect can ingest an infected plant and then move to a non-infected plant and infect it. This cannot be controlled in an outdoor environment.

Dahlia viruses are not spread through water or soil contamination. It is believed that cutting infected plants can spread virus through residues on the cutting implements. Virus can spread through the division and sharing of tubers. A virus infected plant will retain the virus in its tubers across generations.

The American Dahlia Society (ADS) has spent over a million dollars researching and testing for virus. They ask members to submit leaves from their most healthy plants to check for the prevalence of virus in dahlias around the country. Despite testing healthy, asymptomatic plants, the ADS recently found that 87% of the samples were infected with at least one virus.

The ADS found that Dahlia Mosaic Virus (DMV) is the most prevalent virus among dahlias. Importantly, 75% of dahlias infected with DMV had NO symptoms.

Virus testing is available to the public but is prohibitively expensive, costing up to $74 per test. We can observe virus symptoms in the leaves and growing habit of dahlias. Dahlias with leaves that have vein clearing (appears to be light green leaking into the dark green surrounding veins), patterned markings such as concentric circles and lighter colored V's almost certainly have a virus. In addition, dahlias that appear stunted with curling or asymmetrical leaves may be infected with virus.

Now that we've given a review of the current knowledge of virus in dahlias we will venture into opinion. Brace yourself...

  • We assume that 87% of our dahlias are infected. We expect to see symptoms of virus in almost all our plants.
  • We assume that 87% of the dahlias we purchase each year will be infected. We expect to see symptoms of virus in almost every plant we buy.
  • We believe that eventually EVERY dahlia ever grown will be infected by at least one virus.
  • Even when a dahlia doesn't have symptoms, we assume that it is STILL infected. We believe we could cull every symptomatic plant and still have an 87% infection rate.
  • At the current rate of KNOWN infection, we believe it is impossible to eliminate virus from dahlia tuber stock in the US.
  • In our opinion, "starting with clean stock" as advised by the ADS is IMPOSSIBLE to achieve at the current dahlia tuber infection rates.
  • We believe that dahlias, like people, are more able to handle a viral infection when they are healthy and well cared for.
  • We believe that protecting dahlias from insect damage keeps them healthier and reduces viral spread.
  • Virus prevalence is a fact of life and is not a reflection on us as growers or any other dahlia grower.

So what is a dahlia lover to do? Here is our protocol...

  • We fertilize our dahlias as soon as the first set of true leaves appear. We continue fertilizing every 2 weeks until heavy bud set, then reduce to every 4 weeks. Nitrogen keeps dahlias healthy and gives them what they need to grow quickly and manage stress.
  • We preemptively treat our dahlias for pests. We spray our dahlias with spinosad every 2 weeks until the first flowers bloom. After that we spot treat when needed in the evenings to reduce impact on pollinators. We also encourage birds in our field to help keep the insect population down.
  • We do not cull for viral symptoms until after our dahlias have been pinched and had at least two applications of nitrogen. We do not cull plants solely for viral markings on leaves. We only dispose of plants that are growing poorly, are stunted or sickly.
  • In our tuber production field, we sanitize our scissors once per day. Most of our deadheading is done manually without cutting implements by popping blooms off the plant. During tuber dividing, we sanitize our tools between each clump.
  • Our u-pick dahlia field is a separate area and is mostly comprised of dahlias grown from seed. We do not require our visitors to sanitize their scissors.
  • We do not notify other tuber sellers when a tuber we received from them has viral symptoms as it is not possible to know for sure if the virus was acquired in our environment or theirs. We do not seek refunds or replacements for symptomatic plants.

We understand that emotions regarding dahlia virus can be intense. Rationally, our farm cannot afford to dispose of up to 87% of stock every year to chase an impossible standard of "virus free" clean stock. Especially when every dahlia we would replace it with is more than likely infected as well. The vast majority of our dahlias grow enormous plants with dozens of blooms despite likely having a viral infection. It's our opinion that disposing of those healthy plants for viral leaf patterns is a colossal waste, disrespectful of nature and incompatible with operating a profitable business.

If any of this is concerning to you as a tuber buyer, we respectfully ask that you do not purchase dahlia tubers from us. We will happily sell our tubers to other buyers.

Back to Blog