Green mould disease is caused by Trichoderma aggressivum which colonizes mushroom compost and reduces yield. Two Pseudomonas species are associated with mushroom compost: Pseudomonas putida, which stimulates mushroom pinning, and Pseudomonas tolaasii which has a negative effect on crop production. The aim of this work was to characterize T. aggressivum – Pseudomonas interactions as these may be important factors in the development of green mould disease. P. tolaasii supernatant inhibited growth by 57% but P. putida stimulated growth of T.aggressivum by 44%. Tolaasin production was identified in P. tolaasii cultures with a peak at 96 h. Fluorescent microscopy examination of T. aggressivum hyphae revealed that exposure to P. tolaasii supernatant decreased mycelial formation while increasing the abundance of conidia. Label free proteomic analysis of changes in the abundance of T. aggressivum proteins indicated that exposure to P. tolaasii supernatant lead to an oxidative stress response and catabolic enzyme activation (mitochondrial import inner membrane translocase complex (5.7-fold), oxidoreductase (5.2-fold), glucoamylase (5.1-fold)). Exposure of T. aggressivum to P. putida supernatant lead to an increase in the abundance of proteins associated with growth and development (structural constituents of ribosome (20-fold), H/ACA ribonucleoprotein complex subunit (18-fold), DNA binding and nucleosome assembly protein (5.3-fold), and prefoldin (5-fold)). These results indicate that exposure to P. putida can stimulate the growth of T. aggressivum and this interaction may be an important factor in increasing green mould disease in mushroom crops and so reducing yield.