Sick miniature laburnham

This Laburnham anagyroides Aschingeri has suffered like this before. Couldn't find a cause but I think it may have slugs.
It was moved to a newly constructed bed in May this year

Over the past 6 weeks or so it's been getting worse.

Also, the new bed has two Sorbaria Sem which are also looking very unhappy

Have scattered slug killer near the plants but haven't seen any signs of slug activity.
Any ideas would be very welcome

 

Maybe it because its autumn

 

Laburnum's are deciduous Bill, they drop their leaves come autumn and will re-shoot in the spring.

 

Yes, I should have mentioned that its been looking sick for some time. here's a photo taken on 30th August.

 

Looks like insect attack, laburnum often looks a bit tatty at the end of the season, well mine does.