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Abstract Background Meloidogyne incognita greatly restricts the production of protected vegetables in China. Application of biocontrol agent Purpureocillium lilacinum is an important practice to control the nematode; however, instability usually occurs especially in heavily infested field. This study aimed to illustrate the high efficiency of P. lilacinum agent with fumigant Dazomet in vitro. Results P. lilacinum YES-2-14 showed strong parasitic and nematicidal activities to M. incognita. Pre-treatment with Dazomet significantly enhanced the biocontrol effects of the fungus. After fumigation with Dazomet at a dosage of 7.5 mg kg− 1 soil, parasitism of YES-2-14 on M. incognita eggs increased by more than 50%. Meanwhile, when P. lilacinum fermentation filtrate treated following Dazomet fumigation at 10 and 20 mg kg− 1 soil, the mortalities of second-stage juveniles (J2s) increased by 110.2% and 72.7%, respectively. Both Dazomet and P. lilacinum significantly reduced the penetration ability of J2s to tomato roots. When P. lilacinum filtrate used alone, the J2s penetrating into the young roots decreased by 48.8% at 4 dpi; while in the combined treatment, almost no J2 was detected within the roots at 4 dpi and the number of knots reduced by more than 99% at 45 dpi, indicating a synergistic effect of the biocontrol fungus and fumigant. Conclusions Pre-treatment with Dazomet greatly increased the biocontrol efficacy of P. lilacinum to M. incognita. This research provides insight into the efficient management of plant parasitic nematodes and effective use of biocontrol agents.