Hello Everyone. This is my first visit to this site and so I may be posting in the wrong area. If this is the case, whoops. Please, I need some help.

According to the book, 'The House Plant Expert' by Dr DG Hessayon I have a Dieffenbachia picta Camilla and I have been following the care instructions contained within. I have had them (both plant and book) for about four months and the plant has been growing well until the last few days. All of a sudden the lower leaves are yellowing. They are not dry to the touch. Many of the leaves have about a millimetre of 'brown' and yellow on the tips.

It sits in a well-lit spot out of direct sunlight. It is never too cold nor too warm. I water it every week and a couple of months ago I began to feed it every three or four weeks (after repotting it on the day of purchase). It is in a 10" terracotta pot and currently stands at 10" high. As of yesterday I hadn't watered it for a few days.

Last night I dug into the soil at the side of the pot - down to about three inches - to check if it was waterlogged. It was very dry and so I gave it about a half-pint of water. The leaves are continuing to yellow rather quickly. Does anyone know if this plant can be saved? Am I doing something horrendously wrong?

Many thanks for your help