This report is a compilation of six draft papers. They describe laboratory and field work which has demonstrated that soil iron, mobilised under certain unusual conditions, can enter wood products in ground contact, detoxify the preservative and lead to premature decay. Forintek's field test site had been recognised as being highly aggressive towards copper and arsenic-based wood preservatives. Investigation of this phenomenon had revealed that iron was moving into wood from the soil. There were a number of ways in which this could contribute to accelerated decay and a program of research was designed to investigate this phenomenon. Premature failure of CCA- treated wood has been reported from a number of horticultural sites across the world. One such instance occurred in Penticton, B.C. and this was investigated to determine if soil iron might be involved. To eliminate the wide range of soil properties which could affect decay, much of the work has been done with iron, treated wood and brown-rot fungi under laboratory conditions using the soil-block test. Experiments have been designed to eliminate a number of possible effects of iron on the wood, the fungus and the preservative. Brown-rot fungi have then been used as a bioassay to determine which components of the preservative are affected by iron. One instance of premature failure of vineyard posts was investigated by a field survey, chemical analysis of samples and a laboratory experiment on the effect of organic soil amendment. Further soil properties affecting iron uptake have been investigated using small test stakes in containers of soil with a variety of amendments under a range of soil moisture conditions. Iron has been shown to increase the weight loss of CCA- and ACA- treated wood by a brown-rot fungus. It does not directly affect the fungus or the wood, nor does it cause leaching of the preservative. Iron does appear to detoxify the arsenic component of preservatives and may have an effect on copper at low copper and high iron loadings. Soil iron was implicated in the premature failure of vineyard posts. Iron uptake was promoted by continuously wet soil and organic amendments such as wood chips. Such conditions are typical of horticultural operations. These results suggest that North American wood preservation standards should have two levels of ground contact decay hazard as in the Australasian rather than the European system. When the use category system is implemented, horticultural posts should be treated to H5 rather than H4. Until then they should be regarded as "structural elements" and should be treated to the pole standard CSA O80.4 rather than the post standard CSA O80.5.