Viruses are submicroscopic pathogens that infect cells, changing some cell functions. Abutilon, camellia, Nandina (heavenly bamboo), rose, wisteria and many other woody landscape plants may show viral symptoms on occasion.
Identification
Viral pathogens are named after the main or first-recognized host plant and the primary type of damage they cause. For example, Apple mosaic virus and Elm mosaic virus cause an irregular pattern of discoloration in leaves on apple and elm, respectively. Hibiscus chlorotic ringspot and Prunus necrotic ringspot cause small yellow or brownish spots or blotches on the leaves of hibiscus or plants in the rose family, respectively.
Damage is usually noticeable only in flowers or foliage. Infected blossoms or leaves may become discolored, distorted, spotted, streaked, or stunted. For example, the flowers of infected plants sometimes develop green, leaflike structures, as with rose phyllody.
Life cycle
Viruses can be transmitted by insects feeding on plant sap or mechanically in sap that is spread by hand or grafting tools. Viruses also spread in pollen, seed, or vegetative parts of plants, such as through budding and grafting during propagation. Once a plant becomes infected with virus, it usually remains infected throughout its life.
Some viruses have a relatively narrow host range and apparently infect only one genus of plants. Other viruses have a broad host range, such as Impatiens necrotic spot virus and Tomato spotted wilt virus, incompletely understood tospoviruses that infect several hundred genera of mostly herbaceous plants, including many flowering ornamentals.
Damage
Viruses can slow plant growth, but most do not seriously harm woody landscape plants. Herbaceous ornamentals and certain vegetables are more susceptible to serious injury or death from viruses. The variegation or other appearance changes that viruses cause are sometimes considered to be attractive, such as Abutilon mosaic virus.
Solutions
There is no cure or treatment for virus-infected plants in landscapes, and generally none is needed for woody ornamentals. Provide proper cultural care to improve plant vigor or replace infected plants if their growth is unsatisfactory.
Purchase and plant only high-quality, certified virus-free or virus-resistant nursery stock or seeds. Do not graft virus-infected plant parts onto virus-free plants unless you want to introduce the virus.
Although certain viruses are spread by aphids and other insects that suck plant juices, controlling insects is generally not a recommended or effective method of preventing virus infection in woody landscapes. It is very difficult to detect or control insects effectively at the low densities that can spread a virus, and to continually provide control throughout the life of perennial plants, especially of insects like the melon and green peach aphids that spread Cucumber mosaic virus in Nandina and feed on many different plant species.
