What does blight look like?
Check your potato plants regularly for brown patches on the leaves. This is the first sign that they have blight. If it’s more advanced, you may see brown patches on the stems as well, and the leaves will have started to rot.
How to deal with it?
By checking regularly and acting at first sign of infection you might be able to save your crop. Remove affected foliage and get rid of it (burning it is best). Then, try removing a few more of the leaves to allow air to circulate better between plants. Keep an eye on things and with any luck you may have got it under control before it got too bad!
If the crop is badly affected, then it is best to cut off ALL the foliage at the base of the stems. Again, try and burn it or get rid of it in another way. You can leave the potato tubers in the ground for two weeks to let the potato skins harden and then dig them up.
How can I prevent it ?
Spacing is important for airflow to prevent the disease spreading, so make sure you plant your potatoes with plenty of space next year. Remove any yellowing/dying foliage as you see it to prevent things from started. Try blight-resistant varieties too (like Orla).