Virus Symptoms This page contains symptoms produced by various viruses that infect Dahlia. The most common symptom is ‘mosaic’. It is evident by the presence of a mixture of dark green and light green ‘islands’ or patches on leaves. Dahlia Mosaic Virus Symptoms on young plants include Chlorotic, yellow spots and malformed leaves. Infected plants may look stunted. Chlorosis of leaves can be limited in size on the leaves initially and can spread to the rest of the plant. Some leaves may show severe Chlorosis compared to other leaves on the same plant. Severe infection often leads to yellowing of almost all leaves and stunting of plant. Impatiens Necrotic Spot Virus Characteristic Symptom is necrotic ring spots on leaves.