Occurrence of Trichoderma in a Douglas-fir Soil

Trichoderma species were isolated to a depth of 100 cm in soil supporting a Douglas-fir stand in western Oregon. Isolation from Mueller-Durrell (M-D) tubes was rare below 33 cm in May and August and did not occur below 53 cm in November. Most common species were T. viride, T. hamatum, and T. polysporum. Trichoderma viride accounted for 72% of November isolates while T. hamatum dominated May (54%) and August (34%) isolates. Soil dilution plates from 25–30-cm depth produced only one colony of Trichoderma in nearly 2000 observations whereas it was isolated at a frequency of 10% from M-D tubes at that depth.