I have many, many pears on quince. That's mostly because it's so easy to stick a quince cutting in the ground, and it becomes a tree. I have noticed over the years that many of them look a little bit yellow. I know one, really outstanding orchardist from HOS, who is not active on this list, who had a difficult time getting production out of his pears on quince. I have quite the opposite effect. When notice my trees looking kind of yellowish, I apply nitrogen in the most convenient form I know: urea. It has always improved the condition, although it often takes a few weeks or even months. I am wondering if this was his problem, although since we no longer really have in person meet ups with HOS, I don't know if I"ll ever see him again. Have any of the rest of you noticed this effect?
You are talking about the leaves, right?
I've come to realize over the last couple of years, that most of my fruit trees are nitrogen deprived. I would need more guests in order address them all in your preferred manner.
I've got a big bag of Urea from Wilco with which I've been experimenting. The Saijo persimmon seems to really like it.