The mixed mode configurations coupling mechanical, hydric and thermal effects for viscoelastic orthotropic materials like wood is studied. The numerical application are proposed on european species (Abbie Miles alba). The analytical formulation of the energy release rate is introduced by A integrals generalized to mixed mode crack growth. The viscoelastic effects are introduced according to the generalized Kelvin Voigt model. This new formulation is based on conservation laws and real and virtual mechanical and thermal fields. The Mixed Mode Crack Growth specimen, providing the decrease of energy release rate during crack propagation, is considered in order to compute the various mixed mode ratios. The analytical formulation is implemented in finite element software Cast3m and the crack growth is obtained by testing the Griffith criterion rewritten in time domain under orthotropic configuration. As results, the evolution of energy release rate and the stress intensity factors versus crack length and hydric variations are computed for the proposed european wood species.