Powdery mildew - end of week 3 of flower

Try 1tbsp oh hydrogen peroxide 3% with a tablespoon of baking soda and 2 dish soap drips of soap in a liter spary bottle. Shake well and spay on the leaves top and bottom. I also suggest doing a bud wash when you harvest. You can do that by 1 cup of hydrogen peroxide and 1/2 cup of baking soda in a 5 gallon bucket and mix well. Then do a double rinse in 2 other 5 gallon buckets. Clean buckets as needed through the process.