Olive Trees Looking not well

Hi all,
First time post here - looking forward to getting into this forum and learning a lot.
My question is we have quite a few Olive trees in our new place, in Perth on the West Coast of Australia, and some don't look so good. Photos below.
Any ideas on what it could be and a suitable treatment?
Thanks in advance,
Cam

Based on the soil and yellow leaves I checked nitrogen for Olives and that is the main nutritional def. they can have. I think its just nitrogen they need.

A lack of nitrogen (N) is the only common nutritional deficiency in olives.
cesonoma.ucanr.edu/files/27175.pdf

Most probably that is caused by the olive lace bug, they feed on the sap of the leaves and create the characteristic pattern of blotches your trees leaves have.

Here's the description from Olive Business:

Sap-sucking insect that reduces vigour of trees.
Flat with lace-like wings and is no more than 2mm in length.
Resides on underside of leaves.
Causes rusty yellow spotting on top of leaves.
Control includes keeping trees healthy.

You can spray neem oil that has been diluted with water

Hi guys,

Thanks for the quick replies!

I've included a photo of the underneath of one of the leaves - looks to be the insect problem, trick will be when best to spray the trees as it's winter here at the moment.

Also, I'm sure adding Nitrogen won't hurt at all. We are next to the ocean here and the soil is a mix of beach sand and pretty average black sand. Not sure the previous owners did too much in the way of fertilisers.

Cheers,
Cam