I have a houseplant that I can't figure out what the problem is. It is a Schefflera. The leaves on one of the stems will begin to turn brown in the center, which then spreads to all of the leaves on the stem, and eventually the entire stem falls off. There are no insects on the plant and I have sprayed it with a fungicide, which didn't even slow it down. I have grown houseplants all my life and can usually figure out the problem, but this one has me stumped.
Another possible problem is that the soil is too wet near the bottom of the pot, causing root damage that is reflected in the leaves. Scheffs don't much like damp soil, especially in the lower light conditions of indoors.
If this is happening to the lower leaves only, it's usually a sign that the plants stem is growing thicker, and throwing old leaves. As the stem gains diameter, the cellular connection between stem and leaf separates and the leaf dies. That's why when you view old "Scheffs", you more than likely see bare stem except at the very top.