Resistance of Wood from Paraquat-Treated Southern Pines to Subterranean Termites, Decay Fungi, and Marine Borers

Untreated southern yellow pine in soil contact is notorious for its biodeterioration if some type of preventive steps are not taken. Sapwood of slash, longleaf, and loblolly pines cut from living trees treated with paraquat to induce lightwood formation was exposed to subterranean termites, wood-decay fungi, and marine borers. The paraquat was poured into an ax frill that spanned one-third the circumference of the tree. The trees were cut 18 months after treatment and the treated wood exposed in either terrestrial or marine exposures. After 2 years of exposure the wood cut from the untreated (control) trees and the wood cut from the untreated side of the treated trees were completely destroyed by termites, fungi, or both, in terrestrial exposures in Mississippi and Panama. By contrast, only 3 of the 35 lightwood-containing stakes were extensively damaged by termites, fungi, or both, from terrestrial exposures in southern Mississippi, and only 5 of 37 stakes were damaged after 2 years of exposure in Panama. In marine exposures, the wood was covered with the normal sessile community of hard-shelled and soft-bodied organisms and both teredo and pholadmarine borers–damage was much less evident on lightwood-containing samples than on normal wood samples exposed for 2 years in Panama. No limnoria were present in these waters. Lightwood from trees treated with 2.5 percent paraquat was less resistant to subterranean termite decay, fungi, and marine borers than wood from trees treated with either 0.5 or 1.0 percent paraquat.

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