It is not yet clear whether viruses are living organisms or nonliving chemicals. In any case, they damage the plant by destroying the chlorophyll in cells, causing yellowing of leaves. Typical symptoms of viral diseases include smaller than normal leaves and flowers. If a plant becomes sick and dies within just a few days, suspect a virus.
Viruses are spread from plant to plant in a number of ways. Insects often carry them, especially aphids, leafhoppers, mealybugs, and whiteflies. Aphids are the worst offenders; the green peach aphid can carry more than 50 different plant viruses. Viruses can also be carried on your hands or on garden tools.
Symptoms of Viral Diseases
The following symptoms may indicate a viral disease of some kind:
Plant performance is poor, either with small, stunted foliage or with small off-color blossoms.
Sudden death of a plant.
Chlorosis (yellowing of leaves), specifically irregular yellow spots on leaves, often accompanied by leaf curling or excessive branching.
Mosaic yellow-and-green mottling pattern on leaves, stems, or even blossoms.
Dead areas on leaves.
Control of Viral Diseases
Viral diseases cannot be cured. Remove and destroy the infected plants. As with bacterial diseases, remove all the affected plants, even if symptoms are mild. Do not place diseased plants in your compost pile, and clean hands and tools with a bleach solution made up of one part household bleach to four parts water.