Can't reply so replying via question format.

There actually are some sprays that are effective. At work they recently started using a sulfur based one preflower as a preventative and it's working great throughout the entire flower period. Prior to that we were using an essential oil based fungicide to treat outbreaks. It's peppermint and rosemary oil based. It got rid of the PM but didn't prevent it from returning...but it was safe to use during flower.

The simple usage of airflow, however you can accquire it will help way more, i would personally not take something off in flowering if you dont have to. I used chargable USB fans for my greenhouse, but not on cannabis, Used it on spiderflowers, hibiskus (both flowers), all kinds of pepper which i think are pretty similiar in terms of environment. GL

You can thin it out some, just don't go crazy. You'll see some people striping their plants down naked and that's not what you wanna do. The anti-defoliation crowd on here go a little overboard with their overly simplistic "more leaves = more energy" mantra. Like plants don't loose leaves in nature, lol. Plants, like people, tend to produce more energy than they can use. People store excess energy as fats, plants store it as sugars. If we(or plants) couldn't store energy we'd have to constantly feed to stay alive.