When and what to fertilise for Grapevines

Ozbev starts with ...
I have a few fruit trees that haven't done so good in our garden and will address that later. Perth soils are shocking I think it's a nutrient issue.
I have just planted grape vines and they did well until just now with some leaves turning yellow. I have researched and most say grapes don't require a lot of fertiliser but obviously if the leaves a yellowing that is a sign they need help. Firstly is there a specific fertiliser, or do I need to do a soil test? Different sites had different answers.