Disease control within the mushroom industry has become a significant challenge. Diseases of Agaricus bisporus were once controlled with the use of preventative chemical fungicides. However, the number of approved fungicides has significantly reduced. There is an urgent need to find viable alternative treatments, which is the primary aim of this thesis. Two biocontrol strains (Bacillus velezensis QST 713 & Kos) were investigated for their ability to control cobweb disease (Cladobotryum spp.) and dry bubble disease (Lecanicillium fungicola), two major pathogens of cultivated mushrooms. B. velezensis Kos was able to significantly reduce the growth of Cladobotryum and L. fungicola in liquid/plate cultures and resulted in structural damage to fungal hyphae. Lytic enzymes such as subtilisin were identified within the inhibitory component of the B. velezensis culture filtrate (CF). The CF also triggered changes to protein abundance from both pathogens. Proteins associated with stress were increased in abundance compared to the control, while proteins associated with growth were decreased. Similar in vitro responses were recorded for the L. fungicola pathogen in response to B. velezensis QST 713. Biocontrol strains were investigated at a crop level and their efficacy was compared to conventional fungicide treatments. A C. mycophilum isolate highly tolerant to metrafenone, was identified. Metrafenone was shown to be capable of controlling dry bubble disease but not cobweb disease caused by tolerant isolates. Biocontrol treatments based on B. velezensis were shown to significantly control dry bubble disease when disease pressure was low to moderate. However, biocontrol treatments struggled to control both dry bubble and cobweb disease under extreme disease levels. It was determined that the application of biocontrol treatments did not significantly impact casing microbiome dynamics. The lack of persistence of biocontrol strains within the A. bisporus casing may explain the reduced antagonistic abilities of both strains at a crop level. Other integrated pest management strategies such as salting, and disease monitoring were shown to be effective at limiting disease symptoms. Results suggest that biocontrol agents can form part of the future mushroom disease control strategies in combination with increased hygiene and integrated pest management strategies.