PlantLife Online

Answer

Umbrella Trees or Schefflera are normally pretty carefree house plants with little pest issues which makes me lean in the direction of an abiotic disorder e.g. light, nutrients, temperature etc (Basically things we control). Umbrella trees do best in areas with high light with regular watering. Schefflera like moist but not wet soil, it sounds like you are watering the plant properly by not allowing it to sit in standing water. There is a possibility the soil in your pot has become hydrophobic and is actually repelling water causing the water to run through the pot faster than the plant can absorb it. Hydrophobic soil can be caused by fungus or bacteria colonies living in the soil. How long has the plant been in the same soil/pot? If the water drains strait through the pot consider replacing some or all of the soil. Schefflera are known for having aggressive roots, if your plant has been in the same pot for several years it is possible the roots are becoming bound and are have a hard time taking up water and nutrients. You can check the roots of your plant by digging down a couple of inches around the base if you encounter a thick mass or roots and little soil its time to replant. How often do you fertilize? Using a mild formula of liquid fertilizer added to the watering can each time you water will benefit all your houseplants (Use at the recommended rate). If it sounds like your light, water and nutrients are in order check closely for pest they are often small and elusive. Check out the link below for common houseplant pests. Hope this helps.

http://www.ext.colostate.edu/pubs/insect/05595.html