I believe this to be a pest I have not seen in a long time, the false spider mite or Brevipalpus phoenicis.
The symptoms would be:
- usually only seen on Dracaena Marginata
- none of they usual signs of the most common pest: spider mites, no webbing, no grain of salt sized white eggs
- yellowing or chlorotic areas found in the new growth
- if left alone the new growth in the centre becomes brown and dry and plant continues to lose leaves from the newest to oldest
I found this very difficult to control as you often did not know the plant had a problem until it was quite advanced. You may wish to use a magnifying glass to confirm the diagnosis. Note that the eggs are hidden in the leaf tissue.
Usually 4 to 8 clusters of eggs are present, normally deposited in
cracks or the hollow cavities in leaves created when the internal
mesophyll has been destroyed
Control can be attempted by using a mixture of 5 ml of dish soap, 5 ml of isopropyl alcohol (Rubbing alcohol) to 1 liter of water.
Use a rag or cloth and wet in the mixture. Wipe the top and bottom of every leaf with this. Repeat at five to six day intervals at least three times.