The contact remedies like that usually will last in the area of 3 days. I've never gotten long term relief from any of the contact remedies. I've tried h202, milk mix, baking soda, high ph water, sulfur based sprays, and a couple other things. A Myclobutonil based dip and spray worked for me in one dose. Months later still no PM. I've been doing a good job of maintaining a good environment but I've slipped up and let humidity get into the 80s a couple times. Some people say once you get PM you can never get rid of it. I've researched the idea of it, and not found anything concrete. As far as I can tell the systemic treatment worked, and haven't seen it again since. This stuff lasts about 15-20 days I think, so probably avoid it within a month of flowering. The dosage I used was the one it said to use for tomatoes.