Discoloured sunflower leaves

Hi I planted sunflowers a couple of weeks ago and they were growing great. Over the last 2 days the leaves have started to turn brown and discolored. Does anyone know the cause of this and how to treat it ?

 

Looks like pest damage, have a close look.
Could be a leaf miner.

 

Cheers Pete, just had another look imagine these are mites

Will a general pesticide do the job ?

 

Not mites, leaf miners.
If I see them I usually just squash them inside the leaf, not difficult, often they are temporary and dont go on to become an infestation.
If they do, a general insecticide should sort them out.

 

Cheers pete