Competing ectomycorrhizal fungi can cause problems during the commercial production of edible Tuber species infected plants in greenhouses and later when infected plants are transplanted to the field. We investigated the effect of selective fungicides on Tuber borchii, in the presence of Hebeloma sinapizans, both in vitro and during the production of T. borchii infected Quercus pubescens. Oxycarboxin completely suppressed the growth of H. sinapizans but had only a weak fungitoxic effect on the growth of T. borchii both in vitro and on Q. pubescens roots. In contrast, other fungicides either suppressed both fungi or T. borchii more than H. sinapizans.