We have a Japanese umbrella pine that was planted in the fall of 2020. It has been ok since, but I noticed in the fall of 2022 that needles towards the bottom of the tree were falling off. They also looked a bit yellow or brown. The very top of the tree looks fine and the needles are dark green. It has continued looking this way through the winter. Is this how it drops off old growth after a couple of years or is something else lurking? It should have enough well drained soil and we've some organic fertilizer on it and even sprayed it for bugs thinking it might have something like white flies. We are at a loss and need some guidance.