Virus is a very serious problem for bulbs. There is a lack of good information about this subject and many differences of opinion. The general rule is if you have a plant that is virused you should destroy it because the virus can spread to other plants you may have.
Virus sometimes is shown by streaked flowers and foliage. Leaves and stems can be twisted and distorted. On the other hand there are plants that do not show signs of disease. The only sure way to determine whether your plant has a virus is to send it to a lab to be tested.
Viruses can be spread by insects such as aphids, leaf hoppers, and mealy bugs, nematodes, mechanically, and by fungi. It is therefore crucial to control the insects, make sure your tools are clean, and treat soil that had infected plants. Some people feel that plants that are under stress that are carrying a latent virus may begin to show symptoms. Stress could be incorrect watering, lack of light, temperatures outside the range, over fertilization from example. Use caution when you deadhead as they may also be a way to spread disease.
Most sources say that virus is not transmitted in seeds although there is not clear agreement on this. Virused plants are often not very vigorous and therefore may not produce seed. Growing plants from seed is recommended and purchasing only from sources that make an effort to sell virus-free material. If you do buy from a source you are not sure about, isolate your new material and if you have any questions about it, have it tested.
Leaf problems on this Clivia. Photo by Germán Roitman. This Clivia may have more than one problem. Virus can make is susceptible to other things.
Crocus are susceptible to virus disease. This is usually visible in the flowers. This distortion may take the form of twisted petals, streaking (as in tulip fire,) sometimes the flowers are depauperate and fail to open properly. The virus also reveals itself as light and dark blotching in the foliage which is most visible when the foliage first emerges. The pictures here have been manipulated to exagerate the streaking in flower and foliage to make it more apparent. (Massive hike in contrast levels does this.) All crocus pictures courtesy of Tony Goode.
Here is one with distorted petals
The vectors are aphids which find refuge especially on the backs of the leaves. These pictures below show a clean Crocus medius and one that has streaking in the petals that is virused.
The pictures below taken by Germán Roitman show the mottled and streaked leaves of these Hippeastrums
Virus in Phaedranassa, Eucrosia, Eucharis, Stenomesson, Griffinia and Eustephia shows as longitudinal ridges (those leaves are perfectly flat if healthy), besides the mosaic stripes. Virused Phaedranassa photographed by Jennifer Hildebrand
The pictures below show Sparaxis with color breaks in the flowers. These plants were very vigorous and increased rapidly in the garden and I had no idea they were virused. Photo by Mary Sue Ittner
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