Looks like it needs a wash, then a coating of oxalic acid solution, then another wash and maybe some touching up with more oxalic acid solution, followed by another good wash. Leave it to dry over a few days then some restorative coatings of whatever oil/stain/treatment of your choice.
Nice picture, I've taken shots like this many a time to finish off a roll of film, some of which have ended up as surprisingly nice pictures.
Thank you. It's teak. It will have a wash (if it stays dry) and then a rub down with some wire wool and a coat of oil and then in storage for the Winter. I quite like wooden furniture that has a weathered look but as you say, it does need to be looked after. This chair is now at the end of its twentieth season.