someone once told me that when some weeds get stressed they form a wax like cover,and weed control seems to roll right off the leaves and land in the dirt.even when you lower the pressure of the gun.so is a sticker gonna help?and how long is the stuff good for?we've got some at our shop,but its maybe three years old,half used too!! its lesco sticker.well if someone will help me out with any info,mucho grassy-ass,by the way,the weeds are mostly ground ivy,clover,and creepin charlie!!thanks !!!