Effect of moisture content of Douglas-fir heartwood on longitudinal diffusion of boron from fused borate rods

The effect of wood moisture content (MC) on the longitudinal diffusion of boron was investigated in Douglas-fir heartwood blocks equilibrated to MCs ranging from 20 to 100 percent. The blocks were treated with 125, 250, 500, or 1000 mg of fused borate rod, and boron penetration was evaluated after 1 week, 4 weeks, 8 weeks, and 12 weeks by staining with a boron indicator and by chemical analysis. Higher MCs generally resulted in increased longitudinal boron diffusion. Diffusion in blocks at 20 percent MC was minimal; diffusion differed little between 80 and 100 percent MC. The results indicate that boron from fused borate rods will diffuse well through Douglas-fir heartwood when the MC exceeds 40 percent. Fused borate rods appear to have excellent prospects for controlling internal fungi in Douglas-fir poles.

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