HOW DO VIRUS DISEASES LOOK AND WHAT DAMAGE DO THEY CAUSE?
Viruses cause a wide range of symptoms and damage. Symptoms include occasional yellow spots or blotches, mosaics, vein yellowing, yellow line patterns, leaf margin yellowing and necrosis. Plants and roots may be stunted, deformed in shape, leaves may role or cup and blossoms and tubers may be suppressed in size and number. Often virus symptoms can be confused with mineral deficiencies, other cultural problems and insect damage. However, viruses very rarely rot or outright kill their host. Virus names often imply a specific type of disease symptom but in practice many different symptoms can be found with any virus. Identification of specific viruses based on symptoms is difficult because of the variable nature of symptoms. Some of the reasons for symptom differences are: • There are multiple strains of most viruses. We have isolated 5 strains of DMV so far that cause anywhere from no symptoms to severe mosaics and ringspots. • Many dahlias appear to be infected with 2 or more viruses. V
