This paper addresses issues in the microwave phytosanitary treatment of frozen wood. Four eastern Canadian wood species are used: trembling aspen, yellow birch, white birch, and sugar maple. The nonlinear heat conduction problem involving phase changes such as wood freezing is solved by a volumetric specific enthalpy-based finite element method. Dielectric and thermophysical properties are functions of temperature and moisture content. As an application, we studied the dielectric heating of four wood species as a function of moisture content and microwave properties.