A new method of flame weeding in row crops—the air-curtain flamer—was developed and tested by Lalor and Buchele. To approach the design of this machine systematically and to improve the design of other flame weeders, a knowledge of the thermal sensitivity of crops and weeds was needed. Thermal sensitivity of corn and soybeans was studied. Thermal treatments to which these plants were subjected and the resulting thermal damage to their foliage are presented in this paper. The effect of the thermal damage on the ultimate yield of the crops was, however, not studied.