Hello I planted 15 ficus nitida trees about 3 years ago and are doing great apart from one that a couple of weeks ago started to drop almost all its leaves. The trees are all on bubblers and the soil seems moist. The bubblers work I checked. Can anyone provide some help or suggestions about what’s going on? I inspected the trunk and I saw some minor white spots which doesn’t seem like a fungus but clearly something is killing it. The other trees are healthy