Chard with discoloured leaves

I've grown chard for some years - the plants look vigorous and until this summer, have looked very healthy. However, some leaves have been looking burnt at the edges. I wondered if I'd inadvertently used too much fertilizer / compost and it's a kind of scorching. Or is it a disease of some kind. My soil is very well-draining. Any thoughts would be most welcome.

 

I'd say slug/snail damage.
There's not much for them to eat at this time of year, so they're desperate.

 

Hi, that looks like leaf miner damage. I would remove the infected leaves but don't compost them.

 

Often with leaf miner you can see the insect in the tunnels, I just give the leaf a squeeze .
It looks fairly advanced so the actual insect could well be gone now.

 

As above, remove damaged leaves, the plants should survive and will continue to grow through the milder parts of winter. Its a good thing to remove scorched and split outer leaves in Jan/Feb to get a burst of new growth into Spring. I have in previous years past , taken a swap hook to them to have this effect. It also reduces habitat for slugs ....