Green mold (caused by Trichoderma harzianum) is a destructive disease in mushrooms which limits commercial production. The present investigation was carried out to verify the in vitro and in vivo effect of locally available botanicals and bacterial biocontrol agents against this disease. The in vitro evaluation of ethanol extract of botanicals against mycelial growth of T. harzianum at 1, 2, and 3% concentrations showed that Juglans regia and Allium sativum exhibited maximum mycelial growth inhibition of 84.9 and 79.8%, respectively. When the same botanicals were tested against the mycelial growth of A. bisporus, it was observed that J. regia, Curcuma longa, and Azadirachta mellea were least inhibitory (4.66–7.4%). From the in vivo evaluation of plant botanicals at 2% concentration, J. regia and C. longa had the highest average weight (11.8–11.9 g) of a single fruit body and a combined button yield of 11.3–11.9 kg/quintal compost. Among the bacterial bioagents evaluated in vitro, Pseudomonas flourescens, Azotobacter sp., and Bacillus subtilis displayed stimulatory effects of varying degrees on the mycelial growth of A. bisporus but exhibited antagonistic effects on T. harzianum. B. subtilis-38, and P. flourescens-104. Azotobacter-108 caused the highest mycelial growth inhibition of 97.6, 97.4, and 90.3% of T. harzianum, respectively. The current study reveals that the integration of botanical and bacterial antagonists in pathogen-infested white button mushroom casing reduces green mold infection with corresponding yield gains.