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Viruses in plants
Like any living system, plants are susceptible to viral diseases.
Testing for viruses in plants is costly, so diagnosis often is based on
symptoms.
 Some common
symptoms include mottling or mosaics expressed as a variegated pattern of
yellow and green on the leaf, fruit or flower; curled or distorted leaf
tissue that feels thick and rigid, even though the plant appears wilted;
and stunting and distortion, which may appear as abnormally shortened or
deformed leaves, stems or fruit. Ring spots appear as wavy rings or lines
of yellow, white or red throughout leaf tissue. And cankers cause
blackened areas or black streaks to appear on stems.
 Viral
particles won't survive outside its host tissue. That means they need a
vector to move from one plant to another. Vectors include insects, and
pruning and propagating tools that move sap from one plant to another.
Viral particles also can be moved through other plant parts such as seeds,
pollen or the plant itself.
 Common viral
diseases include rose mosaic virus, peony ring spot, common bean mosaic
virus and tomato spotted wilt virus. Rose mosaic virus is transmitted by
sap, while tomato spotted wilt is transported by western flower thrips.
Not all viruses are deadly, but over time, they often debilitate a plant.
For example, rose mosaic virus often makes plants more susceptible to
winter injury.
 Unfortunately, there is no chemical control for viral disease.
The only way to reliably control viral diseases is to remove symptomatic
plants and control the insect vector, if appropriate. When working with
multiple plants, it's always best to clean pruning and propagating tools
to avoid "passing" the virus from one plant to another.
For more information, see the following Colorado State Extension fact sheet(s).
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