Technical Abstract: Thermal defoliation is a potential alternative to chemical defoliation, particularly for organically grown cotton. A two-row prototype thermal defoliation vehicle that forced air at 193°C through cotton was compared to application of a chemical defoliant, s,s,s-tributylphosphorotrithioate (Def), in field plots. The thermal and chemical treatments caused >80% leaf mortality within 24 h and 6 d, respectively. Six days after chemical treatment, leaf abscission was >80%, but abscission in the thermal treatment did not exceed 65% even after 13 d. Regrowth at the bases of defoliated cotton plants occurred in both treatments so that total stalk destruction by cultivation or use of herbicides will have to occur as part of boll weevil management or eradication strategies.