The spotted wilt virus in dahlias affects more than 200 species of vegetable and ornamental plants worldwide. The disease is spread only by thrips. Thrip larvae acquire the virus by feeding on host plants, like dahlias with spotted wilt disease. When the thrips mature, their ability to fly spreads the virus to healthy plants.
Symptoms of Dahlia Wilt Disease
Originally discovered in tomato plants, this viral disease was aptly named the tomato spotted wilt virus (TSWV). In tomato species, this virus causes wilting of the leaves and yellow spots on the fruit.
The name of this disease can be deceptive, though, as gardeners aren’t likely to find that their dahlias are wilting. The presence of thrips on infected plants, coupled with common symptoms, is a better indicator to suspect dahlia wilt disease. Due to their small size, thrips may be hard to see. The trick is to tap the dahlia over a piece of white paper or cloth. The thrips will appear as dark specks.
The most common symptoms of infection from the dahlia spotted wilt virus include:
- Yellow spotting or mottling of leaves
- Necrotic ring spots or lines on leaves
- Malformed leaves
- Deformed or stunted growth of flowers and buds
- Flowers exhibit color breaking (have a streaked appearance)
- Plant loss (primarily of young dahlias)
Definitive diagnosis of the spotted wilt virus in dahlias is difficult since the symptoms mimic other diseases and conditions, including nutrient deficiency. Additionally, dahlias with spotted wilt may be asymptomatic or show few signs of infections. The only true way to detect dahlia spotted wilt virus is by testing tissue samples with an enzyme-linked immunosorbent assay or ELISA test. Your local extension office can help with this.
Controlling Spotted Wilt Virus in Dahlias
Like most viral diseases in plants, there is no cure for dahlia wilt disease. The best course of action is to eliminate plants infected with the dahlia spotted wilt virus.
Greenhouse operators and home gardeners can prevent further spread of the dahlia spotted wilt virus by following these management practices:
- In the greenhouse setting, use yellow sticky tapes to catch thrips and monitor their population levels.
- Implement a thrip larvae control program based on thrip population density.
- Screen greenhouse openings with fine mesh screening to prevent adult thrips from entering.
- Avoid growing garden vegetables and ornamental plants in the same greenhouse.
- Don’t propagate plants infected with the virus even if that portion of the plant looks healthy. (It can still harbor the virus.)
- Eliminate weeds that can serve as host plants.
- Promptly dispose of plants infected with dahlia wilt disease.