Chemical control of root disease of Douglas–fir seedlings in relation to fungus and nematode populations

Seed treatment with thiram reduced post–emergence damping–off, while fumigating forest nursery soils with methyl bromide or DD improved Douglas-fir seedling emergence, shoot and root growth, and decreased the incidence of root disease. At an old site, where corky root develops, the benefits from these fumigants were associated with fewer (a) Xiphinema bakeri and (b) isolates of Cylindrocarpon radicicola. At a new site, decrease in Fusarium root rot and increase in shoot growth were related to reduction of populations of Paratylenchus and Pratylenchus, respectively. In unfumigated soils, Fusarium oxysporum was isolated from diseased and healthy roots.