Dahlia Viruses Page 1

Observable Symptoms

Leaf symptoms include mottling, necrotic and ring spots, bubbly surface, and distortion. Stem symptoms include streaking and soft dark tissue. Plant symptoms include stunting and generalized wilting. These symptoms are also symptoms for a variety of other fungal and bacterial diseases, environmental stresses, and cultural practices.

It is very important to recognize that diagnosis based on symptoms alone is often misleading and dahlia plants can be carriers of a virus and show no symptoms whatsoever.

Many of these symptoms are illustrated by the following photographs.

The pictures that appear on these pages are partial shots of several plants that were tested by Mary Jane Sosler, Plant Clinic Manager, Colorado State University Cooperative Extension Plant Clinic, Jefferson County. Mary Jane has had more than 10 years experience as a plant diagnostician and holds a Masters Degree in Horticulture. She performed serological tests on the plants shown.

Photographs by Ben Lawrence.

The plants tested positive for Tomato Spotted Wilt Virus and Impatiens Necrotic Spot Virus. They were negative with regard to Dahlia Mosaic Virus even though it is very common. Plants that are infected with any virus, should be destroyed!!


The pattern on the leaf in the picture at upper right and on the right is typically referred to as "Oak Leaf". The center vein appears almost normal.


Here on the right the central and major lateral veins are affected.


Here the central vein is involved but very feint signs of other veins becoming involved are evident.


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