Posted: 08/09/2016 at 01:00
That looks like typical powdery mildew damage with one clue being the split fruits. Because you haven't regularly pruned the vine, it is growing too much foliage for the roots to support and therefore isn't getting enough water. This, together with the overcrowded foliage which restricts the flow of air creates perfect conditions for powdery mildew to thrive. Being in a pot is exasperating the situation. It probably needs a good feed too.
I would cut it right back this winter and research pruning methods. They are tough plants and will survive a severe hacking back as long as you do it well before growth starts in the spring, otherwise it will bleed to death. Late November is ideal. Correct pruning is essential if you want a healthy vine and lots of fruit.
Start with the RHS site for basic info.
Given the location against a wall, you should probably use the rod and spur pruning system:
I'm sure you will be able to nurse it back to health though.
Last edited: 08 September 2016 01:05:16