Dahlia Viruses 101!! Unfortunately Dahlias are very prone to disease and viruses. Not only can these diseases be spread from dahlias to dahlia, they can also spread to other plants in your garden. The really tough thing is viruses have the same symptoms as insect pressure, nutrient deficiency, under watering, over watering, herbicide damage etc. the only way to know for sure if your dahlia has a disease is to test it. And tests are pricey!! My motto is, when in doubt throw it out. Disease spread

Pests on Dahlias: How to Deal with Them Without Chemicals (And What to Do When They Don't Bloom)