Disease suppressive composts are known to contain beneficial bacteria that can be antagonistic to plant pathogens. This research evaluated whether Sclerotinia sclerotiorum — commonly known as white mould disease — can be managed using antagonistic bacteria from forestry compost. In vitro and in vivo experiments demonstrated that bacteria from the Pseudomonas and Bacillus genera can inhibit mycelial growth and reduce white mould disease. Extraction of culture filtrates and isolation procedures were performed to identify potential bioactive compounds. Three cyclodipeptides were purified and characterized from culture filtrates of Pseudomonas arsenicoxydans (F9-7). The three cyclodipeptide were L-Val-L-Pro, L-Leu-L-Pro, and L-Phe-L-Pro and they are though to be bioactive compounds responsible for the antagonistic against S. sclerotiorum. The most antagonistic effect was obtained with the cyclodipeptide L-Leu-L-Pro at a concentration of 100 mg/mL. These results indicated a potential for some bacteria to reduce the growth of the fungus and its associated disease on carrots.