[Solved] fence clearing with a flame gun
There's plenty of experience with flame weeding crops, maize, onions, garlic especially. Tiny weeds kill easily and can be weeded from those crops without harming the crop. Grasses are tougher to kill. Brush would be very tough to kill, the leaves would be easy to kill if not wet, but the stems will take tens of seconds to minutes to kill with heat.
Wall-E with a magnifying glass is what you'd need