This study was conducted to assess the likely inhibitory effects of vesicular-arbuscular mycorrhizal fungus (VAM), acibenzolar-s-methyl (Bion®), and Rhizolex® 50WP fungicide against Pythium debaryanum pathogen. The results showed that the inoculation with VAM was able to markedly decrease the growth of the pathogen. Bion showed high antifungal efficacy against Pythium debaryanum Oomycete. The seedlings of Pinus roxburghii that were inoculated with VAM displayed the highest growth parameters in terms of shoot height, root dry weight, and total dry weight in both seasons, followed by the treated seedlings with Bion in both seasons. The enzymatic tests revealed that mycorrhiza and Bion were able to significantly enhance levels of enzyme activities related to disease resistance, including peroxidase and polyphenol oxidase, which were clearly increased compared with the control. Mycorrhiza showed a higher effect on increasing enzyme activities related to disease resistance than Bion. Total phenols increased in all treatments as compared to the nonmycorrhizal, non-pathogen-treated control, but were highest when plants were inoculated with both the mycorrhizal fungi and the pathogen. This study recommends VAM as an inoculum for increasing the productivity performance of P. roxburghii seedlings and controlling the growth of P. debaryanum.