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This is another long and involved topic.  Sometimes you don't even know that you have a problem until a significant amount of damage has occurred.  The best way to become aware of problems is to examine your plants on a regular schedule.  This is easy when they are in bloom but the other nine months are just as important.  Try and make a habit of looking at your plants at least once a week.  This is easy when you hand water but needs to be done even when you bottom water.
There is another aspect of dealing with pests that you need to decide about.  If you have Disas, you are going to be stuck using fungicides and insecticides to control problems.  I don't like to use chemicals mainly because as a former chemist, I have a very healthy respect for organic chemicals.  I have had to overcome my personal bias against the use of chemicals, and once I did, I have noticed a definite improvement in my plants' appearance.  I basically advocate a prophylactic approach where you don't let problems build, but spray the whole greenhouse or growing area as soon as you notice a single problem.  This goes for insects, fungi, or snails/slugs.   But don't apply chemicals without protection!  I always have all skin covered and use an Army surplus gas mask with the appropriate organic cartridge.  Don't forget to turn off your fans when you are spraying.
I find that I'm using a few compounds that seem to work reasonably well under my circumstances.  My first  tool is a mixture of Knox-Out and Orthene WP.  Knox-out is a microencapsulated Diazinon insecticide and Orthene WP is a broad range systemic insecticide.  They mix well together if you use a little liquid soap as a sticker.  The idea is that the Knox Out is effective for up to a week and by then the systemic function of Orthene is taking effect.

In general, the following chemicals have worked with Disas: Orthene WP, Malathion, Knox-Out, Mesurol WP, Banrot, Clearys 3336, Dithane 45, Subdue, and Captan.  I have also been using a new/old tool in my battle with fungus.  As most orchid folks know, powdered sulfur and cinnamon are two common items found around the house that act as fungicides.  Well, powdered sulfur doesn't do much against this particular fungus I've had to fight lately,  but cinnamon seems like it may have a beneficial effect.  I have been using it where the fungal infection is in the center of the plant and therefore not able to be cut out.  It seems like when cinnamon is used, the new leaves grow right thru the cinnamon and are unaffected by the fungus which appears to dry up.
Be careful with Physan 20, and Neem oil.  They seem to damage the plants. I continue to use Physan 20 with my deflasked seedlings but at very low dosage (about 10 drops / gallon) and I wash it off after potting.

Some of the problems that you need to look for include:

	Ants: Where you see ants, you will eventually have a problem. They are constantly bringing in aphids, scale and mealy bug.  I try and spray around the base of my benches with a Daizonian product to keep them at bay.
	Slugs and snails: Slugs and snails are always a problem but usually are easy to see with a flashlight at night.  The new iron phosphate slug bait seems to work really well for slugs and snails.  I have used the Sluggo product and it's amazing to see the slugs crawl out of the moss and go directly to the bait and start munching away.  Mesurol is another product that can be used as both a slug killer and an insecticide as well as a bird repellent but it is hard to find in the States.
	Earwigs: My most aggravating problem is earwigs. They only are a problem when you have plants in spike getting ready to bloom.  They get in at the base of a flower stalk and chew it enough that the stalk starts to rot.  Nasty things, kill all you find. They are relatively easy to spot if you look for dark droppings in the sheath around the flower stalk.  Hand picking with a small forceps works well.  I also think that the use of "Knox-Out" which is a micro encapsulated Diasonium product, works well.
	Aphids: A nasty side effect of having ants around.  I use both the Knox Out / Orthene mix and alternate it with straight Malathion.
	Thrips: Another nasty little creature.  Orthene WP works well.
	Spittle bugs: Controlled really well with Knox-Out / Orthene mixture.
	Fungus Gnats: Controlled really well with Knox-Out / Orthene mixture.
	Mealy bugs: These shouldn't be a problem but they always seem to show up.  They usually appear during the summer warmth and are easily controlled with the Knox Out / Orthene mixture.
	Fungal Infections: Colletotrichum gloeosporioides is a very nasty fungus that can sweep through your collection very quickly.  It is characterized by small brown spots that quickly become halo ringed and then quickly turn the whole leaf brown and shortly thereafter, kill the plant. This is an example of an early occurrence of the fungus.  If left untreated, the infection will spread to the other older leaves first and during the blooming season, will form brown spots on the bud ends and prevent normal opening.  Some effected buds can be seen in Volume #22 of the DisaPhile for 2001. This amount of infection took only about two week from when it was first noticed on an outer leaf.  It spreads quickly. The little brown spot where the leaf bends is an early warning sign.  Any leaves that show the little halo ringed brown spot at the bend should be removed as soon as you see it and give the whole collection a spray of Dithane.   This shows another plant which showed no sign of infection two weeks earlier.  Once infected, there is no way to reverse the process so the infected leaves must be removed and discarded well away from the plants.   This plant is showing the effects of an infection.  Note the fact that a large number of leaves are starting to turn brown.  A closer examination will reveal that a lot of the brown spots have the halo effect and after the halo or bullseye is formed, the center will just quickly rot away leaving marks like something sucked the sap out of the leaf. Notice also the tip of the flower.  It initially was stuck to the bud and only reluctantly opened.  In plants having advanced infections the bud will have a brown spot on the end of the bud While I hope the description is clear, you can read about the organism further at: http://www.extento.hawaii.edu/kbase/reports/damping_pest.htm My personal recommendations for controlling this organism are as follows: 1):  Isolate the infected plants if possible. 2):  Trim off all infected leaves.  I know this sounds drastic but if the leaves are already infected, it will just spread.  You can't reverse the process of infection. 3):  Spray the whole collection, top and bottom of leaves, with a product called Dithane (sometimes called Mancozeb).  I had a hard time getting this product and finally got Dithane 45 which is a liquid.  I used 1 tablespoon per gallon of spray.  I also added 10 drops of Physan 20 which also acts as a dispersing agent.  Since writing this I have located the wettable power and it seems to work slightly better. 4):  Repeat the spraying weekly on all plants for two or three weeks or until you don't see any new occurrence of the fungus. This depends a lot on how bad you have it and how far it has spread.  I had a fairly bad case of it last year because it took a while to identify the problem.  The pictures above showed up in the fall after about two weeks of inattention and I took the plants right away and sprayed the whole collection once and haven't seen any new outbreak in the subsequent month.  5):  Try and decrease the humidity by adding a little heat at night if possible for a while until you clear it up.  Alternatively, you can decrease your misting. 6):  It's probably a good idea to start to include Dithane in your regular fungicide spraying program.  I normally spray prophylactically once a month during the cool months, trying to vary the fungicides used.  That should cure the problem. The fungus is a lot more common than a lot of growers realize.  I was interested to find that Sid Cywes also sprays with this product as a preventative during the winter months and the symptoms also showed up in a New Zealand collection.

	Moss: Any time you top water, you are subject to attack by various Mosses.  These can quickly out grow the Disas and then they form a barrier to good aeration as well as providing a safe harbor for bugs and slugs.  One reason for considering bottom watering.
	Liverworts: I noticed a lot of this growing on the tops of pots in New Zealand.  I'm not sure if it is as problematical as moss here in the northern hemisphere, but it has to interfere with the take up of nutrients and the exchange of gases.  It seems to bother growers who have colder climates more than here in the Bay area where I essentially don't have the problem.
	Oxalis: This is a particularly troublesome pest as it 's roots quickly invade a pot and when you try and remove it, you cut through the much more fragile Disa roots.  Get it early or repot to remove completely.
	Weeds: Definitely remove as soon as you see them.  I have a lot of problems with this little weed that grows quickly and shoots seeds all over the place.  Don't know what it is called but it's a real pain.