Answer: Based on your description I am not certain what has happened. Schefflera will sometimes develop disease problems if kept too wet, including root and stem rot. Leaf yellowing and droppping can be a signal of the soil being too wet or poorly drained. But since this is only affecting one stem it is difficult to identify the cause, especially long distance. If the stem is black and soft and rotting, trim it off below the discoloration. Then clean your knife or pruner in rubbing alcohol to prevent possibly carrying the infection to another plant. Make sure the plant is not overwatered, and be sure the drain holes in the bottom of the container are not blocked. Also empty the saucer beneath the pot after watering, do not let the plant sit in water. You might also want to consult with your local county extension to see if they can give you a more specific diagnosis.
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