I second what Jen said. I live in the desert with a lot of rock landscaping, and clay soil under it. No way I can reasonably pull a weed from the rocks along with getting its long tap
root out of the hard clay soil here.
I've been using a flame thrower weeder for the last ten years or so. The idea isn't to burn the weed to a black crisp, only to transition the green leaves to a darker green color. Something about it being better to put the plant/weed into shock rather than kill the top only. It's more likely the plant will put its
energy into repairing itself, which should end up being a lost cause. I find that I have to go through and flame the same area twice within a week or so. That way any plants that are making a comeback get hit again and are pretty much goners.
Again, like Jen said, my main weed problem is in the spring. I'm pretty much weed free (unless already established/mature) by June. Nothing is going to grow from seed in the summer unless we get consistent monsoon rain, and that hasn't happened for the last three years here.
I also like the idea of cooking the weed seeds with the torch. If I do see a weed in flower, I make sure to bbq the flower/seed.
The bad part. The first time I used the flame thrower, I set a windmill palm on fire (holy smokes the dry stringy trunk lit up like a rag soaked in
gasoline after getting a little close to it). It was in my urban front yard, rock all around it, and I had the hose nearby that was already pressurized so I was able to put it out almost immediately. I did have a black trunked palm tree for a year, lol. It was fine, and only a few of the lower fronds suffered heat damage.
I also made the mistake of using it near my wood chip mulch once. Got a little too close to the woodchips, must have not noticed some chips got heated
enough to smolder, fifteen minutes later I see smoke coming from behind my garden shed, and sure enough a few square feet of wood chip mulch was burning steadily. I lost a newly planted female pistachio, and almost lost my shed.
I do not use the flame thrower anywhere near my wood chips anymore. It's just too hot and dry here.