In the agriculture world, application of harpin proteins (https://www3.epa.gov/pesticides/chem_search/reg_actions/regi...) can be used to help treat diseases by inducing a defense response. Mind you, it’s not a standalone treatment, but helps make applications of fungicides and the like far more effective.

Pathogen defenses can roughly be thought of having a metabolic cost at the very least. Meaning if there’s no selection pressure (such as death) otherwise, then it often ends up being more optimal to not have a defense active until it’s needed.

Problem is we have a global distribution system that is forcing organisms that have previously evolved into an equilibrium with the disease complex in their area, to encounter multiple novel threats in rapid succession. Like how aggressive species of downy and powdery mildews are now everywhere in the US. Giving plants a boost by inducing defenses early on helps them resist the onset of infection and helps treatment succeed.