Mine didn't do very well this year either...Powder mildew even though they are completely in the open...Most of mine look like yours...I don't know what caused this, but I think I'm going to get rid of mine and use the space for another type of flower.

I hope someone can help out...knotz

Looks like powdery mildew to me (disclaimer: I'm no expert though). I used baking soda in water to spray on my heavily mildewed squash leaves this year (next to my dahlia bed which I sprayed too, just in case) and within days I saw recovery and my dahlias never got the mildew.
I used the recipe from previous forum post: 5 Tbsp. baking soda + 1 gallon water
The 5 Tbsp. sounded like a lot to me (thought it might be 5 tsp. instead) but I didn't see any detrimental effect on the squash or dahlias.

thera

Thanks All! Knotz, I think I am going to get rid of these after I dig them up as well. Never happened before.. Don't want a repeat next season :)

It doesn't look like powdery mildew to me. Looks more like spider mites. In either case, it won't affect the tubers, so don't throw away (unless you're looking for a reason to get some new ones). But -- you should cut down the plants and get rid of the debris. DON'T COMPOST IT!!

I never compost any dahlia debris, just in case there is some disease or bug in it. I had dahlia smut this year for the first time, and I will be very careful to clean everything off the ground when I dig. Luckily I live in the country and can burn.

Teresa

That's what mine looked like too. I thought it was the heat. First timer with Dahlias here...only 2 plants. I cut them back...not even thinking they were coming back. They are now growing again. So I'm going to try to winter them.