My expectation for roadside weed control in a subtropical area is at least 6 months of bare ground. No vines, grasses or invasive trees coming back in an area treated with herbicides. In a temperate area with seasons, the expectation is for year long control.
They who can give up essential liberty to obtain a little temporary safety, deserve neither liberty nor safety.
Benjamin Franklin 1775
Sell not virtue to purchase wealth, nor Liberty to purchase power.
Benjamin Franklin Poor Richard's Almanac1738