Question
i have had a euphorbia erytrea for a yr and it has been doing fine- grown about 2-3 inches. it is a warmn room in our flat and i water it when the soil gets rock hard/dry.
tonight it has started suddenly looking a bit sick- browny appearance and white fluffy mould ascending up from the base.
i think it has a fungal infection. cant see any insects.
can you help please - i think it is goin to die!!

Answer
For whatever reason, it sounds like your plant has rot.  I doubt the sickness was sudden.  Fungus usually starts in the roots and works it's way up.  It's often hard to figure out why and by the time you see it it's too late.  What you can do is unpot the the plant and see if the roots are white, fat and healthy and if the brown part is still hard.  If so you might have a slight chance of saving it by spraying with fungicide and repotting in new sterilized soil and a new pot.  Euphorbias, by the way, don't like to get rock hard/dry.  They do require less water in the winter, but don't like to completely dry out like cactus.  Anyway, if it's the case that the roots are bad, the tissue is soft, etc. then i suggest you get out a sharp knife, sterilize it with alcohol and make a sharp cut 3-4 inches above the rotting part to healthy tissue. Resterilize again if you need to cut more. Let that callous over for about 2 weeks and repot in well drained, sterilized potting medium.  Plant deeply enough in slightly moist soil to hold the plant upright and then just mist. In a couple of weeks you can gently tug and if there is resistance. That means rooting has started.  Do that every two weeks or so until you feel the resistance and than gradually start watering.  You will know that you plant is doing well by new growth more than anything else.  Keep it out of direct sunlight till then and gradually move it toward bright, but not hot sunlight.

If your apartment is warm and dry mist your plant very few days or so and water when the soil is dry to the touch to about an inch down.  Don't over water but also don't under water as you have been.

Good luck.
Maureen