Mehltau in meinem grow Raum

There's no killing it. There is no effective method to 100% kill off 'white powdery mildew' (WPM, hereafter). At best you can slow it down. More often than not, spraying a plant with various remedies will only spread it around to the stems as it drips all over. Even if the leaves look clean, temporarily, the mycelium network that grew underneath the leaf surface will regrow the hyphae above the leaf surface within days. Plus, now you have WPM on stems and petioles and anything else that foliar spray dripped onto, including flower. Amputate. Don't spray. Be gentle to reduce spread of spores while you do it. Up to you if you want to try to finish.. depends on how quickly it's spreading and how much time is left. consider an early harvest if some portion is salvageable. None of the holistic formulas work -- for example the "cornell formula" is utter bullshit. changing pH of leaf surface in various ways also won't be effective no matter what you read on the internet. The stuff only commercial farmers have access to buy is only 25-33% effective at slowing it down. Anything you read promising a solution is simply not true. Those peopel smoked mildew-riddled weed and are lying to themselves. Also, "washing" the buds does nothign useful at harvest. It's still tained, fucked up weed. So, cut off what you can and pray, but no god is coming to help you. Future tip -- WPM is almost always caused by a poorly controlled environment. Most likely, condensation is occuring after lights go out and temperature drops coinciding with an uncontrolled relative humidity percentage. As temps drop, RH spikes to the point condensation occurs. If this happens every night, it virtually gaurantees WPM. So, control your RH better in future. Get a wireless temp/rh probe you can read after lights out without disturbing photoperiods in flower. You can see if RH is spiking to dangerous levels without interrupting the dark cycle. Also, use your trichome loupe/magnifier. Inspect buds. If you see what looks like a fuzzy netting over the trichomes, it's infected with mold, too. Anything tainted with WPM should be thrown out. It will irritate lungs and the weed will be total shit.