Trichoderma harzianum has long been studied as a possible biocontrol agent against wood degrading fungi, and has provided varying degrees of protection in several European field trials. In laboratory trials, however, this fungus appears to be less active against white rot fungi. This characteristic was studied using a wood wafer sandwich procedure which simultaneously expose ponderosa pine sapwood wafers with and without exogenous nutrients, to both the biocontrol agent and Trametes versicolor. The results indicated that the biocontrol agent limited but did not completely inhibit weight loss by the decay fungus. Extracts of fungal exposed wafers indicated that the bioprotectant appeared to stimulate laccase production by the white rot fungus. Laccase production is normally associated with secondary metabolism induced by depletion of one or more nutrients in the substrate. The biocontrol agent apparently stimulated this process, thereby potentially accelerating the decay process. The implications of these results with regard to long term biocontrol performance are discussed.

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