SCREAM

I went into my greenhouse today and spotted mealy bug on a handful of
cacti.........how can i get rid of them ? I have a can of spray stuff (cant
recall the name offhand) but it says to 'water well prior to spraying'. As
the cacti are now to be kept dry till spring what can i do ? There are too
many for me to pick them off, i havent got that much time free!

I like to be 'organic' so dont routinely spray to debug 'just in
case'.....is this my downfall ?

M