Just tried my new Stihl FS 91 trimmer. Cut some heavy tall grass around my farm. Not quite the power I thought it would have but decent. I have alot of Burdocks and heavy viney type weeds. I bought a grass and brushcuttet blade as well. Im assuming the grass blade is what I want to cut the burdocks and weeds? Any advice. I will try to attach a pic of blade.