The mauget system is great for the most part. Trees smaller than 3 inches in circumference is permissible with injection as long as you are using the micro-tips. Anything less than 3 inches is better off with soil injections of Merit. As for a IPM procedure, if the trees and shrubbery is in tight spaces or around water front areas, then injection using Merit product caplets is the way to go, however it will control most of the troublesome insect.
I have seen contracts like these that only want one application of insect control product used per season. This works pretty well considering the property owner's has been used to paying for one app with Merit. They need to remember that disease and fungus isn't included in tree/plant health care and always be on the lookout for things to pop up.
For me; small trees less than 3 inches gets the backpack folar treatment, shrubbery also. Trees that are larger of course, gets the injections. Early season timing is critical for allowing the Merit to translocate into the xylem and phloem. You may want to look into a product called pentrabark.
I don't know if I would assure complete IPM services based on a one time shot.! That is just my 2 cents.