I don't know what this is, Diplodia sapinea is not a rust it is in the family Botryosphaeriaceae (Ascomycota). Diplodia sapinea produces blue staining of the timber (under the bark), the image here appears to show superficial colouration on the bark surface that may or not be associated with a gum exudate. Examination under a microscope may show if there is a microorganism involved. There is a recent paper on Diplodia sapinea here: Wingfield, M.J., Slippers, B., Barnes, I. et al. The Pine Pathogen Diplodia sapinea: Expanding Frontiers. Curr. For. Rep. 11, 2 (2025). https://doi.org/10.1007/s40725-024-00236-2
