I have a lemon tree which I raised from seed (store-bought). It is about 3 years old and around 60-70 cm tall. It has done quite well, and seems to be less finicky than my grapefruit tree. However, in the last few weeks, it dropped quite a few leaves. The dropped leaves seemed to simply dry out and die. They did not turn yellow. They retain their dark green hue but simply get all crunchy and fall off. I'm wondering if this is WLD and I should treat it as such, or if it is something else. The tree sits underneath a heating vent, so occasionally (no more than 15 min a day) it gets hot, dry air blown on it, but I always spray the plant when the heat goes on. I've reduced the watering schedule a bit for the winter. Any help would be appreciated.