It looks like your tree is deficient in an immobile nutrient (such as iron, and I think iron-deficiency is likely). That's usually what causes the new growth to grow yellow. You might also test the pH of the soil. While you're at it, if you'd rather be sure, you could do a soil test for nutrient deficiencies to see if it's iron that's the issue, or something else. You can test soil pH and nutrient deficiencies all at once.

I'd recommend something like ferrous sulfate heptahydrate to treat iron-deficiency (it's probably less expensive than many iron treatments; plus, it includes sulfur, so if sulfur-deficiency is your problem, it'll take care of that):

https://www.greenwaybiotech.com/produ...

I've tried the kind at that link (not on trees, but on other plants, and I liked the effects).

Immobile nutrients include at least the following (but the way the deficiency looks can be different):

* Iron
* Sulfur
* Boron
* Copper
* Calcium

Iron deficiency is pretty common in trees, I've found.

It's possibly caused by too much of something you've given the tree. I mean, I've seen symptoms like that on a tree given way too much wood ash (which can raise the soil pH). Other things used to raise soil pH might have caused it, too; e.g. lime. It's possible some chemicals might cause it, too. Check out this link about soil pH and iron deficiency (it also mentions soil compaction being a potential cause): http://denvertrees.com/treeology/post...

Anyway, I'm fairly confident that this is not caused by a fungal infection, nor a pest, nor a bacterial infection, and probably not a virus.

People usually use sulfur to reduce the pH of soils (potentially a lot of sulfur, such as elemental sulfur); I'm not talking about treating sulfur deficiency. Lowering the soil pH with sulfur takes a long time. I like to add peat moss for a more immediate solution; it adds acidic bulk to the soil, at the very least (and may or may not just be a short-term solution); that's what we added to the soil where that apple tree was to help things to grow in it (and we spread it around to mix with other soils, to dilute the ash). A little ash can be good, but a lot is a problem.