I did the same with woven fabric, scuffed the plant up and sprayed. Think I may have even used a bit of fairy in the mix one year - probably you who suggested it! I don't know if its a gradual process less infested each year but after around 3 or 4 years spraying it I can't remember getting it the last year. That's not to say I didn't get other weeds though! Is this what you've found it reduces over time?