My 17hand hunter has it, you can imagine how easy a horse that tall makes it to get at his ears......

He was seen by the head equine vet at the Royal vet college when we lived down south as they were our vets for the horses at the yard we were at.
He said that putting the creams etc on can often do more harm than good, as it makes them earshy (or more earshy!).
Since then, we have managed it with full ear cotton fly fringes to keep the tiny blackflies which cause the plaques out of his ears, and also by putting on his bridle in 2 parts in summer when its worst, undoing at the cheekpieces to split it. First part (headpiece, browband & top half cheekpieces is popped on first, and then bit and noseband section, doing up the cheekpieces last. It sounds a hassle but is the best way to ensure you are not bending the ears which is very painful for horses with a lot of plaques. You might not need to do this if it isnt as widespead.
Mind you at least my chaps are just a layer in the ear, the eventer Headley Britannia who won Badminton and Burleigh 3 day events a couple of years back
has them coming right out of her ears :-O and she has her bridle put on in 2 bits too.
Def worth getting your own vets opinion too as vets do vary on this but we've chosen to manage it rather than try and blast it, partly cos with 17 hander you can afford for him to get any worse earshy than they have to. I should say tho that this summer hes decided he wants me to clean out gunk from his ears when he comes in from the field, which is amazing as we couldnt touch them till recently.