I had an aphid invasion this year, which resulted in shriveled leaves. Have you checked for aphids? They are tiny and light yellow in color. They hang out on the underside of the leaf.

No suggestions, but you may want to check for stem rot. I had the same thing happen, no one had any suggestions. The thing was growing vigorously, then all of a sudden, the top was wilting and dying back. Upon further investigation, the stem appeared to be rotting from the top down!! Very strange!!

I got no advice here, so I decided to err on the side of caution, and pulled it. I thought I would just cut it back to the tuber, but ended up damaging it, so that was all she wrote. **sigh*** RIP little lady!!

Thanks for the replies. Yep, they are turning brown from top with shriveled leaves. They are not even a foot in height. Sigh! So much for my interest in Dahlias. I will check for aphids too.

I dug up and saw the tubers were rotting. Too much water I guess. Anyway lesson learned. Thank you both.