The best prevention is daily inspection!
Not too practical, but looking them over while watering helps already.
If I were to see Root Mealy bugs, replacing the medium would be first on my list and while doing so, gently wash the stuff off the roots. I would give the plant a good soak with the Bayer Advanced Rose and Flower care
http://www.bayeradvanced.com/f...
That will help also to keep Ant population down which is often responsible for farming all sorts of scale Insects.
I usually do this treatment once a year, mainly on my Cattleyas, before I bring them inside in the Fall.
Now all year around, whenever I see a small Mealies and Scale infestation starting, I give it a squirt with All Season Horticultural Spray Oil. I always keep a spray bottle of this around for spot cleaning.
Other people here surely have their favorite bug killers, the most important thing is to remember that after prolonged usage of the same stuff those little buggers start loving it and laugh into your face.
Now on my Cattleyas I try to remove a lot of the skin covering the pseudobulbs, since bugs hide underneath it.
Seriously, I come back to the beginning, it is best to keep a sharp eye on your plants and try not to miss funny looking white dots which start to wiggle. No joke.
