Activity of Two Strobilurin Fungicides Against Three Species of Decay Fungi in Agar Plate Tests

IRG/WP 17-30704

J D Tang, T Ciaramitaro, M Tomaso-Peterson, S V Diehl

The objective of this study was to examine the toxicity of strobilurin fungicides against wood decay fungi in order to assess their potential to act as a co-biocide for copper-based wood protection. Two strobilurin fungicides, Heritage (50% azoxystrobin active ingredient) and Insignia (20% pyraclostrobin active ingredients), and copper sulfate pentahydrate were tested against one white rot fungus (Trametes versicolor) and two brown rot fungi (Gloeophyllum trabeum and Fibroporia radiculosa). SHAM (salicylhydroxamic acid) was also included in the study because it is a known potentiator of strobilurin activity. All treatments were incorporated in an agar-based media and evaluated for their effects on mycelial growth rate. Based on minimum inhibitory concentration values found for F. radiculosa (a copper-tolerant fungus), Insignia was 5.5x more toxic than Heritage. SHAM at 100 ppm, increased toxicity 9x for Heritage and 1.2x for Insignia. In a 20-day toxicity screening study, the four one-compound treatments tested were: copper sulfate (5000 ppm), Heritage (20 ppm), Insignia (20 ppm) and SHAM (100 ppm). The two two-compound treatments were: Heritage + SHAM and Insignia + SHAM. The two three-compound treatments were: copper sulfate + Heritage + SHAM and copper sulfate + Insignia + SHAM. For the two copper-susceptible fungi (T. versicolor and G. trabeum), the treatments that caused complete growth inhibition were copper sulfate alone and the two three-compound treatments (copper sulfate + Heritage + SHAM and copper sulfate + Insignia + SHAM). For F. radiculosa, the two- and three-compound treatments were the most toxic, with maximum daily average growth rates statistically similar to the copper sulfate treatment. A key result, however, was that only the three-compound treatment of copper sulfate + Insignia + SHAM completely inhibited growth of the copper-tolerant fungus. Thus, it appears that pyraclostrobin, which is the active ingredient in Insignia, has greater potential than azoxystrobin to act as a co-biocide for completely inhibiting growth of a copper-tolerant fungus.

Keywords: wood protection, decay fungi, copper tolerance, strobilurin

Conference: 17-06-04/08 Ghent, Belgium

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