Background Lecanicillium fungicola is a fungal pathogen of the white button mushroom ( Agaricus bisporus ) and causes dry bubble disease. Due to the recent withdrawal of approval for the most common fungicide prochloraz, only one approved fungicide, metrafenone can be used on mushroom crops within the European Union. Biocontrol uses antagonist bacteria and is being evaluated as a sustainable alternative to fungicides. Bacillus velezensis (QST 713) is the active agent in a commercially available biocontrol product, while B. velezensis (Kos) is a novel strain. Both have shown antagonistic activity against L. fungicola in vitro . The aim of this work was to evaluate the management of dry bubble disease during large scale crop trials using both fungicide and biocontrol treatments and using a range of inoculation levels to establish a level which best reflects on-farm conditions. Results An inoculation rate of 1 × 10 4 conidia m −2 applied on day 12 was determined to reflect disease conditions on mushroom farms most closely. At this inoculation rate, the fungicide metrafenone achieved efficacy levels of 96%. Biocontrol treatments Kos and QST 713 were also able to significantly reduce disease development ( p < 0.05) and resulted in efficacy levels of 74% and 86% respectively. Applying salt to diseased areas on the beds significantly prevented disease outbreak (efficacy 73%), demonstrating that this is a technique which growers should continue to employ. Conclusion This work provides important information to the mushroom sector on the treatment of dry bubble disease and provides suggestions to researchers when considering inoculation levels to include for testing biocontrol treatments at a crop level.