Copper remains a key component used in wood preservatives available today. However, the observed tolerance of several critical wood rotting organisms continues to be problematic. Tolerance to copper has been linked to the production and accumulation of oxalate, which precipitates copper into insoluble copper-oxalate crystals, thus inactivating copper ions. The purpose of this study was to assess differences in oxalate production and decay capacity of four wood decay fungi (three copper-tolerant and one copper-sensitive) exposed to various applications of copper. Three Fibroporia radiculosa isolates and one Gloeophyllum trabeum isolate were subjected to one formulation of copper citrate presented to the test fungi by four different treatments in Southern pine wood blocks for an eight week period. Samples were evaluated for oxalate production and weight loss every two weeks. Two of the copper-tolerant isolates evaded the inhibitory effects of all four copper treatments by week eight. The copper-sensitive organism exhibited some limitations to actively decay blocks in two of the four copper treatments. These findings suggest that proximity to copper citrate, available in any form (i.e. impregnation, direct contact, free liquid or close proximity) generally, had no negative effect on fungal growth, oxalate production, and decay capacity of the copper-tolerant organisms. Results also suggested that the copper-sensitive fungus was restricted in its ability to effectively decay wood when copper was pressure treated or directly added to the surface of wood blocks. This study also suggested that close proximity to copper alone (i.e. not pressure treated) did not completely inhibit decay of the copper-tolerant or copper-sensitive test fungi.
Jenkins, Katie M.; Clausen, Carol A.; Green III, Frederick. 2014. The effects of copper proximity on oxalate production in Fibroporia radiculosa. The International Research Group on wood Protection, section 1, Biology, IRG/WP 14-10823; 2014; pp. 2-12.