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Aims:  To maximize spore production by Bacillus amyloliquefaciens B128, and its antagonism to the fungal pathogen Botrytis elliptica B061. Methods and Results:  In the 5‐l stirred‐tank bioreactor (STR), with the 0·5 vvm aeration rate, an agitation rate of 200 rev min−1 significantly enhanced the spore yield compared to the same in 300 rev min−1 cultivations. In a 20‐l airlift bioreactor (ALR) the maximal spore production was further increased with a controlled aeration rate of 2·5 vvm operated in a 24‐mesh net‐draft tube mode, and no pH control cultivation. This spore yield in the 20‐l ALR was five‐ and eightfold higher; in addition the cultivation period was 19 h shorter, compared to that obtained from shaker flask and in the 5‐l STR cultivations respectively. Conclusions:  Although culture conditions are still to be optimized, by using an ALR with net‐draft tube, a scaling up from shaker flasks and STR to ALR of spore production by the strain B128 is technically feasible. Significance and Impact of the Study:  The spore yields obtained using bioreactors were much higher than those previously reported. The freshly produced spore preparations from the B128 strain significantly antagonized the grey mould pathogen B. elliptica.