Noticed one branch with yellowing leaves, now there are several limbs with dying leaves. Leaves are turning yellow or brown around the edges, then look get a variegated look with green, yellow and brown, finally turning competely brown. Within the past two or three weeks, there are several more limbs with the same ailment. Seems to start at the outward tip of limb and work inward. No mites noticeable. No sign of black spots. Help.