By Mualla Berksoy, PhD and Courtney Calahoo, PhD, June 26, 2026
Each individual active ingredient, copper and boron of CobraTMRod has been long established as an effective biocide in timber preservation. Furthermore, broad spectrum biocidal activity against a wide variety of fungi, mold and insects has been reported with the assumption that borate-sensitive species are not copper-sensitive and vice-versa. Yet, the effect of boron and copper combined is more than the sum of its parts. When formulated together, copper and boron exhibit synergistic activity, with each contributing to the overall efficacy of the formulation. Studies have shown that this synergistic activity provides greater efficacy than either active ingredient alone under the conditions evaluated. Similar synergistic activity has also been reported for the prevention of sapstain and mold growth.
Recently, the synergy of copper and boron working together in Cobra Rod was compared quantitatively to the sum of their individual effects. The toxic thresholds, or minimum inhibitory concentrations (MIC) against brown rot fungus Gloephyllum trabeum (G. trabeum) of CuB glass was studied in a collaboration with U of A research groups [1], and using the same technique copper and boron were also measured individually. MIC values for the same fungus were 0.277 g/L elemental copper, 1.328 g/L boric acid and 0.7 g/L CuB glass. In 0.7g/L of CuB glass there is 0.016 g/L elemental copper (Cu) and 1.033 g/L boric acid equivalents (BAE). The difference in bar heights in Fig. 1. confirms that the Cobra Rod glassy formulation of copper and boron compounds demonstrated greater antifungal activity under the study conditions than its individual parts: only 17 times less copper and approximately ¾ of BAE are needed to achieve the same protection.
As known from literature, the combination also achieves both the diffusion and permanence required in a perseveration formulation: boron diffuses along with water into the wood, penetrating deeply; once inside, the copper “fixes” and immobilizes the boron. Therefore, our vitrified formulation of Cobra Rod offers a long-lasting and easy-to-handle option: in glassy form, copper oxides reduce the dissolution rate of the formulation demonstrating significantly more leach-resistant than its corresponding water-soluble boron compound.
Additionally, the fusion of copper and borate mineral forms a new glassy compound, with Cu-O-B bonds throughout the Cobra Rod which address formulation challenges associated with water-soluble boron compounds and water-insoluble copper compounds, and result in higher solubility.
1. Tom Y. C. Zhao; Nadir Erbilgin; Guncha Ishangulyyeva; Courtney Calahoo; Mualla Berksoy; Angelica C. Bendezu Cevallos; Hongbo Zeng and Ravin Narain, “Screening Technique for Evaluating Copper-Borate Glass Against Brown Rot Fungi and Bacteria”, International Biodeterioration & Biodegradation 214 (2026) 106390
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