(taken from the ISU extension Sustainable Urban Landscapes publication, Hosta Diseases and Pests) Viruses are very tiny particles, too small to be seen except under an electron microscope. Viruses are incapable of reproducing on their own; instead, they invade plant cells and induce these host cells to produce more virus particles. They then cause disease in plants by disrupting normal cell function, which results in symptom development and a decline in plant health.
Viruses can be transmitted during vegetative propagation if an infected plant is used as the source of propagation material. They also can be transmitted mechanically by moving plant sap that contains virus particles. Viruses also can be carried in seeds and pollen and by pests that feed on plants and move infected plant sap from plant to plant, like nematodes, insects, and mites.
Viruses often shorten the lifespan of plants or reduce growth, but they rarely are lethal. Symptoms may also be affected by environmental conditions. Some common viruses found on hosta are, Hosta virus X (HVX), Impatiens necrotic spot virus (INSV), Tomato ringspot virus (ToRSV), Tobacco rattle virus (TRV), and Arabis mosaic virus (ArMV).
The best method to manage virus diseases is to avoid introducing these pathogens into the nursery or landscape. Only use virus-free plants for propagation to avoid transmitting viruses to new plants. If symptomatic plants are found in a nursery or landscape, they should be removed and destroyed so that the virus cannot be transmitted to healthy plants. Weeds are known to harbor many different types of viruses, so keeping weeds out of hosta beds will help, as well. There are no pesticides available to control virus diseases in plants.