25 yr old Macadamia Nut Tree . Zone 18. Last 2 yrs had leaf chlorosis, weak if any flowers, no nuts formed. No signs of disease. End
of life cycle No signs of disease in roots, trunk, etc, but leaves make the tree look like it's dying. pH 6.23, P and Zn high off the charts, low N ( have been adding feather meal over the last 6 months to no avail.) All other nutrients are within or nearly in target area.
Your foliage looks like it has a combination of nutritional deficiency, foliage disease (possibly anthracnose).
You may need to do soil analysis and you may need the help of an Arborist to determine the specific disease cause and treatment plan.
This article has more information.
You may also want to contact your County Extension Office to see if they have any help for these diseases in your region.