Growing tomatoes one time under cover had a huge problem with white fly, not an unusual infestation, but a very stubborn one. While using the natural kinds may be better, pesticides are often a necessity in that situation. Your comment was completely on target for many commercial producers.
This may turn out to be a silly question, but how does a pest infest a closed system in the first place? Do they arrive in the soil? Do they fly in the door?
Could there be ways to mitigate or prevent the mechanism of infestation in the first place?
- People's boots/clothes.
- The water.
- The soil/fertiliser.
- The air.
Each of those inputs would need to be filtered. And the cost of filtration (or the entry/exit protocols for the workers) would need to be balanced against the cost of losing a crop.
Fungal spores are everywhere. And in hot humid high CO2 environment where there are no other kinds of fungal spores to compete with, and a big giant buffet of the kind of food they like...
Nom nom nom nom.
Same thing goes for insects.
Nature is constant warfare. Farming is like picking a side and arming it.