I do use this product since last year that i have plants are infected with leaf septoria and PM as well. I used spray, not concerate liquid one.
I sprayed with it 3 weeks before harvest....no problem after all serenade is organic...plus its really stinky and smell remind me of bleach....
and recently i have same problem- leaf septoria again....same thing like last year...but one thing i grow different strains...this particluar strain got burned from it...i mean bad and i had to defoliated about 8 or 10 nodes along with branches....learned my lesson...I would suggest to start with dilute with water down...so you can read the plant for react.
this product is solid.