Preplant soil treatments were implemented to determine effects on populations of potentiallypathogenic Fusarium and potentially disease-suppressive Trichoderma spp. as well as root colonization by these and other selected fungi on healthy-appearing, bare root 2-0 western white pine seedlings at the USDA Forest Service Nursery, Coeur d'Alene, Idaho. Soil treatments included fumigation with dazomet, bare fallowing with periodic cultivation, steam treatment, fallowing with amendments of Trichoderma harzianum biocontrol agents (BioTrek® and University of Idaho isolates [UI]), and incorporation of two cultivars of winter Brassica cover crops followed by biocontrol amendments (UI). Soil Fusarium populations were significantly reduced by dazomet fumigation; fallowing with biocontrol amendments and incorporating winter mustard crops with biocontrol amendments resulted in significantly higher Fusarium populations. Trichoderma populations were significantly decreased by dazomet fumigation, bare fallowing and steam treatment. Incorporation of Brassica crops did not significantly affect soli Trichoderma populations. Level of Fusarium root colonization was significantly reduced by dazomet fumigation and steam treatment. High levels of root colonization by rhizosphere-inhabiting isolates of Cylindrocarpon were common in some treatments. Assaying root colonization by selected fungi may supplement other parameters to evaluate effectiveness of soil treatments implemented to reduce pathogen populations and improve conifer seedling production.