Unfortunately, at present it is difficult to state which viruses are the most serious because to do so requires observation of many dahlia cultivars infected with specific virus isolates. However, at present we have only a few virus free plants to work with. It will take time to free material of virus and propagate sufficient material for testing of virus isolates against specific dahlia clones. Also, the question is difficult to answer because there are virus isolates that do not appear to be causing significant damage. However symptomless virus isolates are a problem because they may not be symptomless on all dahlia cultivars. The virus is just waiting for a chance to infect some new introduction to the garden. It is also possible that some viruses may affect plant and blossoms in some valued way.