Efficacy of Trichoderma harzianum as a biological control of Fusarium oxysporum in container-grown Douglas-fir seedlings

Inoculating a soilless medium with encapsulated Trichoderma harzianum did not affect any aspect of Douglas-fir (Pseudotsuga menziesii var. glauca [Beissn.] Franco) seed germination or subsequent growth. Results of inoculating medium with a known pathogenic isolate of Fusarium oxysporum alone, or concurrently with T. harzianum, were the same: high levels of damping-off, low amounts of hypocotyl and root disease in midsummer, and significant reductions in height growth. When seedling roots grew through T. harzianum-inoculated medium before growing into a mixture of T. harzianum-F. oxysporum-inoculated medium, mortality was reduced about 50%. Although contamination by resident Fusarium occurred, subsequent root colonization was significantly reduced in T. harzianum-amended growing medium.