Despite efforts of eradication and sanitation, Phytophthora ramorum persists in the United States and has been a problem in commercial nurseries since 2001. Detection in a nursery immediately causes the nursery to be under quarantine until the P. ramorum can be proven to be eradicated. Treatment with the biological control agent Trichoderma asperellum showed promise in laboratory results to remediate P. ramorum-infested potting soil. Sixteen T. asperellum isolates were screened, found to have variable mycoparasitic activities, and further tested in natural field settings. Field plots having P. ramorum-infested soil were treated with T. asperellum, a chemical and two different commercial biological control products and compared to non-treated infested soil. After 8 weeks, P. ramorum populations were not detected in the soil treated with T. asperellum isolate 04-22 showing that T. asperellum isolate 04-22 could remediate soils infested with P. ramorum under natural field conditions.