Dahlia help identify problem

The leaves are turning brown and crispy is this disease or lack of water or simply dying back. What's my nexy step
Thanks

 

Possibly red spider mites.
Have a very close look at the under side of the leaves for webbing and tiny insects.
You might need a lens to see them, they are very small.

 

thanks will give this a go

 

an update,
all the leaves turned brown and went crispy and the remaining bulbs did not flower. This spread to the adjacent dahlias
can I save the tubers?
should I cut them back?
amy help would be appreciated

 

Still looks like Red spider mite to me.

 

looked under the leaves as you suggested but didn't see any.

 

Red spider mite are very small and you may need a hand lens to see.
At this time of year I would put them somewhere sheltered to dry off, then lift tubers, let these dry, then wrap in newspaper and keep cool and frost free over winter.

 

when i lift the tubers i will take pics and post.

 

Are they special plants and worth saving or better to get fresh clean tubers or seed for next spring ?

The tubers may be very small through lack or water and might not survive storage too well.

 

In that case then why not chance leaving them in the ground then.
When the 1st frost has blackened the leaves cut it right back ( I tend to leave a tiny bit above the soil line so I can definitely identify where they are). Next cover them with mulch, compost, leaves and finally I top the pile with a large upturned pot...if it's a plastic one I put a brick on top to make sure it doesn't get blown over/ away.
I always do this and so far I have never lost one yet.

 

I'm new to this topic but I have a question, I have just planted 10 Dahlia tubers only 3 of which I could identify with feeders. I planted them 4-5 inches deep was I too soon as the temp during the night has dropped to 3dgs ?

 

"with feeders"? not sure what you mean by this.
Too early? depends where you are in the country. If the weather smiles on you and you are frost free after the shoots emerge watch out for slugs and snails.
Hope you planted them somewhere free draining as until they start to grow and produce roots the tubers are vulnerable to rot in cold damp conditions.
Most of my dahlias are still in storage in the greenhouse. The ones in the ground outside won't appear until May.