Hi, have you kept them well watered ?, the browning could be a number of things, sun scorch, if they have been allowed to dry out, the plant could be getting rid of them, are they in pots, or in the ground ?, were they potbound when you planted them out, if in the ground ?, and if so did you scratch the roots to free them up a bit, to stop them going round in circles, in which case they wont be able to pick up enough water and nutrients, Derek.

also are there any grubs eating away in the leaf where the brown patches are?

Could it be leaf miner damage? Pick off the damaged leaves and destroy just in case its that. (Don't know if it affects Pelargoniums though)

Thanks everyone, they are in terracotta pots, will try to water them more, was under the impression that they were Mediterranean plants and could be kept on the dry side, new compost and only planted out a few weeks ago.

The slow release fertilizer pellets are a better choice for pelargoiniums. Sprinkle a few pellets in the pot and you never have to think about fertilizer again. It's good for the whole season. Too much all at once will burn the leaves which is what I think we are looking at. Avoid splashing fertilizer on the leaves. Snip off those damaged leaves and it should recover. They are very resilient plants. Let them dry out between waterings. When the leaves look a little droopy, give them a good watering if you don't get enough rain - July & August.

Stem cutting will root very easily so you can start new plants.