Could be stem rot which I had in a plant one year. The advice I got was to destroy the plant, which I did eventually. It never rebounded, and for good reason- the stem was basically rotting from the inside out.

The symptoms you describe are very similar to this, though I don't recall yellow leaves. Look for discoloration or weakness in the main stem wall. If it's other than that, someone else will chime in.
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"destroy the plant" - Does that include the tuber?

It did mean destroying the tuber too, for me, because it was well on its way to rotting when I pulled it up. I think it was jroot who had this happen once and he relayed it affected the whole plant going right down to the tuber. Better safe than sorry.

Thanks poochella. Btw, Your garden is gorgeous.

You're welcome, but sorry for the loss of your dahlia.

My planted areas look like a mess to me: never will be lovely formal gardens, more like basic cultivated planting areas. But that's how it goes when you live on rock-filled clay soil.

Here's the new dahlia bed coming along. It's hard to envision grass surrounding rows of lovely flowers, but that's my hope, once the soil dries out,the mud goes away and all that soil gets put in place.
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New veggie mix soil hauled in by machine! Saved me hours of hard labor loading and unloading it myself.

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I can't say how many kitty litter buckets I've loaded and hauled with rocks sifted from this bed, but I'd wager it's easily in the 200 range and more to go...

Close up of the "soil" but I must say this was one of the worst areas: couldn't even shovel here without bouncing off rocks. I'm very appreciative of the fine wonderful stuff that emerges when the rocks get taken out.

I will never, ever do this again. I have enough planting room now if not for dahlias for veggies which have taken a back seat to flowers.
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