Yes, however, you don't want to! You only want to heat the leaves of the weed in need of removal. If the weed is "burned to a crisp", the plant will shut down its photosynthesis system (process in which a plant produces its energy to survive and thrive), only to grow back from the unharmed root a few days later. The flaming process is a slow kill. By heating the leaves, you disrupt the structure of the cells therefore killing the plant and the roots from which it grows. It will take only a few days for weeds to dry up.
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