Seven species of Trichoderma were isolated from roots of 104 live Doug
las-fir (Pseudotsuga menziesii) trees infected with laminated root rot
caused by Phellinus weirii. The trees were treated 10 years earlier w
ith one of three fumigants: Vorlex, methylisothiocyanate, or chioropic
rin. Sample chips from root sections appearing to be stained or decaye
d by P. weirii were plated on malt agar. Most (73%) of the Trichoderma
spp. isolated were T. viride. Though not tested statistically, Tricho
derma spp. were isolated more often from fumigated trees than from non
fumigated trees. In root sections of nonfumigated trees, Trichoderma s
pp. were isolated significantly less often where P. weirii was viable
than where it was not.