If your Raspberry leaves are starting to look like this, kind of variegated and in some cases a bit yellow, they probably have an iron deficiency, and possibly a manganese deficiency too. I know because mine look like this!
I first noticed it a few weeks ago and actually thought it made the whole plant look a bit more interesting. But I looked it up in my edition of ‘Growing Fruit’. And, yep, there it was, iron deficiency.
The book recommended reducing the amount of water I gave to the plants in the short term and in the long term applying iron sulphate (bought from garden centre) to increase the iron in the soil. And if that doesn’t cure it some Epsom Salts to top up the manganese.
I will also be culling the canes (again) this Winter as I still have way too many Raspberries and I think the close proximity to each other is aggravating their growing conditions. It’s all go in the Raspberry bed right now!