Not sure about the black spots, but the puckering and twisting would have me yanking it out of the ground for sure. Healthy leaves are flat with no noticeable vein coloration.

There are at least seven viruses that plague dahlias, and each have slightly different symptoms. They offer testing right now, $300 for 30 leaf samples. Believe it or not, that is subsidized substantially (normally $60 per sample) by friends of the American Dahlia Society. This test will identify how many viruses are infecting each sample... yes, you read it correctly... it is possible for multiple viruses to be plaguing one plant, with no cure. To top it off, it is depressing to report that some very clean plants with no virus sign at all can STILL be found with viruses!

For those of us who don't care to pay for a test that only confirms a plant's virus status, the overwhelming 'call to action' is... "When in doubt, Throw it out." It hurts, I know. I'm up to the 45 plant mark that I've tossed, mostly from recently purchased or traded tubers. I'm averaging about 10% of my stock that is tossed due to possible viral infection every season. Next year, I'm going to segregate all the NEW stock to their own bed, so I lower the risk of contagion due to bugs transmitting virus or me disbudding and cutting blooms.

Well, I have to admit I was hoping for a different answer. Very upsetting. At least it is one I can replace.

I hear you... upsetting and can be heart-wrenching when its a rare variety that has been long-awaited. I have two plants of one such variety that needs to be pulled, and I need to take a deep breath and yank. Nothing easy about it.

It used to be that serious growers would blame nutrient deficiencies for every viral symptom they saw. They'd feed heavily, and 'voila!', the symptom would disappear. Research has shown that feeding simply masks the incurable virus. Its slowly being accepted that yanking ANY suspected plant is the best course of action, as testing has shown extremely high virus results in those plants that showed any virus sign in the garden.

Keeping good records is helpful, as it would be only to easy to end up buying/trading the same virused stock for the next season, going through the same angst all over again. I know I've done that on about five varieties this year, as I just didn't bother going through tons of correspondence to match up the previous year with the next.

This one was a 2nd year that I originally got from Swan Island. I do not recall it having any problems last year, but it didn't make a lot of tubers (that might have been my fault, I got it on "sale" in June and didn't plant it until July, and then planted it in only partial sun) and only one of the tubers survived until this year. I cut off the blooms and brought them in (because they are too, too gorgeous to waste, took a breath, and pulled it out this morning. The flower name is Gabrielle Marie. Have you heard of it?

http://www.dahlias.net/dahwebpg/Disease/Virus4.htm This may be old information but I thought it was very useful. No? I think I might look at fungus pests and treatment if you are unsure.