I'm in the process of growing the little apple tree you see here from a seed that had germinated within an apple I was eating. I thought it would be interesting to see if it would grow and over the past two years it has seemingly done quite well. It recently came out of dormancy and sprouted an entirely new arm.
However, now the leaves on the new arm are turning brown from the edges in and slowing falling off. I don't understand why it seems to be struggling, it gets regular water (not too much), has lots of direct sunlight, and is fertilized with a 6-2-4 mixture designed for fruit trees.
The odd thing is that the other two limbs seem to be doing fine, with little to no browning or drying out.
Does anyone have any ideas or suggestions?