Black edges of leaves on broadbeans?

[kippers garden]

I have noticed today that 3 or 4 of my broad beans sown at the beginning of April in separate pots outside have black edges on the leaves.  They almost look like they have been slightly burnt. 

Does anyone know what this is and what I need to do?

[kippers garden]

[tim]

More like frost or windburn than Rust or Chocolate Spot?

[Meg]

Leave them and they will be fine

[kippers garden]

Thanks... i  hope they will be ok