Despite efforts of eradication and sanitation, Phytophthora ramorum persists in the United States and
abroad. Fungicides have limited effectiveness, but there are concerns that they may only inhibit pathogen
growth and hasten resistance development after repeated fungicide applications. Biological control is an
active control measure that can work continuously as long as the agent is alive and active. The goal of this
study was to examine whether Trichoderma spp. have the potential as a biological control agent against
P. ramorum. Sixteen Trichoderma spp. isolates were screened for mycoparasitism of P. ramorum in a dual
culture assay. The different Trichoderma spp. isolates demonstrated variable mycoparasitic activities with
some isolates showing no activity while others completely eliminated the pathogen after 4 weeks. Seven
isolates of T. asperellum were consistent among replicated trials in eliminating recovery of P. ramorum
from the exposed agar plugs and preventing leaf disk necrosis. Further testing of six T. asperellum isolates
against two different P. ramorum isolates (A1 and A2 mating types) resulted in the same high level of
mycoparasitic activity. Soil assays involving P. ramorum-infested potting mix and selected Trichoderma
spp. isolates demonstrated that two isolates (04-22 and 02-64) were consistent among the repetitions
to eliminate P. ramorum propagules to non-detectable levels. Based on these results, specific T. asperellum
isolates have the potential to remediate P. ramorum-infested soil and have the potential to be developed
into a commercially-viable product.