Weeds going to seed and my shovel won't do the job... torch?

I have lots of weeds growing in a particular corner of pasture. I'd like to shovel it, but it would take hours and I don't have the time. I noticed just today that they are beginning to bloom.
Is there another way I could deal with these to keep them from spreading? I'm wondering if I torch only the top portion, would this stop them from dropping seeds and spreading?

Those flame thrower torches should work.
You don't need to burn the weed (wastes propane).
Just a good heating - enough to sizzle-pop the stem usually does the trick.

Just make certain to do this BEFORE they go to seed.
Some seeds actually germinate better after being torched, so if they have seeded, you'll need to really burn them.

A scythe would make quick wok of the job.

Thanks for the replies. I like the idea of a scythe, but they are forming a "bulb", sort of purple at the top, should this be of concern if I were to use a scythe? Around this time last year I went "ninja" on the whole patch with two machetes. It was a lot of fun and exercise, but they grew back. So in chopping them, am I "helping" them to spread, or do they just decompose? I figure since the thistle harvest this year appears to have grown by almost 2x in this particular area, that I either helped them to spread or they somehow spread/grew from the root system.

On another note, if I were to chop them and use them in an 18 day compost, would I have contamination in the compost of these weeds? I just watched "Permaculture Soils" and saw that weeds could be used and I'm not too sure of this (though trust the info coming from Lawton, just don't understand how the weeds will not contaminate).

The bulbs on the head of a canadian thistle, if not destroyed, will bloom, pollinate, develop seeds, and multiply. Take them out now using whatever means is available to you.