David wrote:

I put some fertiliser on my lawn yesterday and it was windy. Over night I
find my curb stones are now stained brown - quite badly in places.

Always read the instructions.

Any advice on how to get these stains off ........ I am nearly in tears.

It is tricky. Most things that will remove the iron stain will attack
concrete or limestone too. The least aggressive thing that might work is
citric acid available from any wine making shop.

No guarantee though. Iron stains are remarkably resilient and the
attempts to clean it off may cause other colour changes. Try any
proposed treatment on a sacrificial corner. Whatever you use rinse well
afterwards or you will get the iron stain back over a wider area!

You could also try turning the iron stain damage nearly black by adding
tannins (cold tea) - it might disguise it on an old limestone pavement.
Or at least avoid doing this by accident if it isn't what you want...

Regards,
Martin Brown