One approach to the biological control of decay in standing poles, live trees or seedlings is with microbial immunising commensals or IC.·These are microorganisms able to grow in the wood without damaging it and as a result of such growth to protect against certain types of decay. Scytalidium and Trichoderma spp have been tested in the field. The latter species have shown an establishment rate in excess of 80% in field tests made with standing creosote treated poles during the past 4 years. In live trees, higher rates can be expected. These IC are known for their antagonistic properties against various Basidiomycetes and their innocuity to man and environment.