I've been looking all over trying to figure out what this is. This is a picture of a honeycrisp apple that is 3yrs old. We've been having a really hot year this year so I thought maybe it was heat stress. I also thought iron or nitrogen deficiency. Are there any leaf readers out there?
nitrogen deficiency is yellowing of the leaves, iron is yellowing of the leaves with green veins. The brown spots are not related.
Where i live nobody seems to know what im talking about when I say ferrous sulfate, so I had to resort to grinding up iron vitamin tablets and dissolving them with vinegar before mixing with allot of water. It saved my raspberry's twice and I did my fruittrees before they had a chance to show signs.
grinding up the iron tablet is something you can do tonight, try tomorrow and thee the results in 3 days, if you can get the sulfate that would be great and need less reapplication.