Modelling the control of decay in freshly felled pine poles
M W Schoeman, W Van der Werf, J F Webber, D J Dickinson
In a recent study investigating control of decay in freshly felled pine utility poles, it became apparent that the efficacy of different treatment methods was strongly related to the size of the material being treated. A topical application of 5% w/v disodium octaborate tetrahydrate (DOT), brush applied to the cut surfaces of logs with otherwise intact bark was just as effective at excluding white rot colonisation in large diameter logs (greater than 30 cm) as it was in small diameter material (less than 15 cm diameter). In both instances, protection was effective for at least 12 months. In contrast, a biological treatment consisting of a spore suspension of a specially selected isolate of Trichoderma viride, was only effective in preventing white rot when applied to the small diameter logs. In larger logs, the extent of decay in biologically treated material was as high as that evident in the untreated controls. To ascertain why the effectiveness of the biological control was dependent on the diameter of material being protected, a simple mathematical model, describing both the growth of the Trichoderma and decay basidiomycetes, was devised. In addition to providing a valuable insight into the dynamics of biological control, this modelling exercise highlighted the benefits of applying such an approach to wood protection.