Was thinking of getting a long-handled propane burner for this purpose, that is until our neighbour around the corner did his about back in April..!!
Long story short, some weeds near his shed, the one next to the fence and where he keeps the bbq gas bottle and the burner, kept smouldering late into the evening, the shed caught fire, the flames from the shed spread to the fence and between the two they set fire to the roof eaves of the neighbouring house, completely destroying the roof just before the gas bottles exploded and took out the kitchen and some bedroom windows of our friends house.
Took six fire engines, including one of those special fire platform trucks, bit like something out of Thunderbirds, two to three hours to put out the roof, shed and fence fires. Water damage to the house means the upstairs was completely ruined. Our friend has had the repairs done to their flooring and windows now, but the house is covered in scaffolding and plastic sheeting and won’t be finished until early next year, or so we're told.
Suspect I’ll be sticking to conventional weed killer.