Many dahlias are resistant to viruses of different types. They may display very mild symptoms but grow just fine. Other varieties are stunted terribly by the same virus. When a variety has a virus and it displays no symptoms, the insects can spread that virus to virus susceptible plants. They call the the virus spreading things "vectors". The act of cutting flowers is not generally listed as a virus vector. Humans are infected with very many viruses that give us no symptoms. So are plants.

I have a virused plant whose leaves are crinkled and splotched, and extra Magnesium and foliar fertilizer did not improve its condition. I wanted to see it bloom before digging and tossing the plant.

Are you saying, Ted, that sterilizing tools or even tossing the plant is useless since the virus has already had the opportunity to be spread by bugs? Kind of like sending a kid to his room after sneezing on the uncarved Thanksgiving turkey won't keep family from getting sick, perhaps.

Many people equate dahlia virus with the Black Plague. They think that once it starts all your plants will be infected and die within a few days. In reality it spreads rather slowly and most of your plants already have one or more viruses and show few or no symptoms. Any plant that is seriously stunted or has an extreme case of blotchy foliage should be tossed as it susceptible to that virus. You can try the Magnesium or extra fertilizer but if it is really stunted it probably will not work.

Hello Ted, thanks for your answer, I am really reliefed that cutting flowers is not a vector. And fingers crossed I didn't have any black flies/ aphids this season. So I will get some epsom salt or something similar and just keep the nice flowering ones that keep going.
Well, thanks again, bye, Lin