Scale is usually controllable with oil sprays (coats them so they cannot breathe). Takes a follow-up or two in my experience, but my experience does not include many orchids (although I was doing very well with the one at work; even got it to set a new plant after this years flower

)
Once we go chemical we begin to lose the bacteria, fungii and protozoans that Nature uses to store nutrient. We have become so inculcated with chemical thinking that we tend to think of soils as a place to put the rootd and store the chemicals, but it is a complex, self balancing ecosystem that turns sunshine into plant food (as all energy IS solar energy at some point; I.e., coal is old plants that did'nt get turned into plant food and the energy comes from plant material that grew a long time ago, but under the same sun we see today). It is the conversion of decaying plant matter into microbiological entities, and the resulting trophic predation releases plant nutrition. This is Nature's model for fertilization...
Your move to organic inputs, however unnatural the process that brought them there, fits that system. When you include Osmocote you add ammonia salts, not a regular addition in natural systems, and we start to see mortality all along the trophic chain in the soil. Now the plant is entirely reliant on the ammonia salts as natural systems become suppressed. Osmocote's slow release will ameliorate this effect some, but it will make it constant rather than the boom and bust of water soluble nitrogen which washes away with the first watering (which is why they invented Osmocote in the first place).
So phase it out and be done with it, my friend. It does you, the soil, the plant or the planet little good, and Mother Nature is always right about these things, no matter how deep we humans pile our hubris. This is her realm, these plants and fungii and bacteria, and we can learn a lot from her and find greater successes working with her than bucking the natural system...
Remember, Fritz Haber was making bombs, not plant fertilizer...
HG