Dahlia,fungus ?

I have some dahlias in a tub and they appear to be wilting due to a fungus/mould, the other dahlias in pots appear to be ok (images attached).
Is this down to me? over watering/deheading to far down stem?

Any ideas.

 

I wonder if they are suffering from being too wet Scudo. Is the drainage partially blocked?

It is odd about dahlias.....I grow several now and some in pots. Never have a problem with them in the open ground but in pots a couple seem to suffer a little. Literally 2 plants and these were the same affected last year so I put it down to variety. Seeing them begin to suffer in mid summer I cut half or so of the top foliage back, some unhealthy looking stems right back, cleaned up around the base and applied sustained release food granules. Since then they have recovered beautifully ...healthy and loads of buds to open.

For the affected varieties I decided they needed to be deadheaded asap....i.e.before they can drop their old flower heads into the foliage. This keeps foliage clear and well ventilated (this is important I feel) and, therefore, healthy.

 

I think the drainage is ok but I did water daily during the hot spell, having said that the others are ok. I will cut back and clean up debris and see what happens.

 

This dahlia was looking much like yours Scudo some 3 or 4 weeks ago. Now healthy and full of buds