The fungicide chlorothalonil was evaluated as a wood preservative to prevent attack by the Formosan subterranean termite, Coptotermes formosanus Shiraki (Isoptera: Rhinotermitidae). Southern yellow pine wafers treated with chlorothalonil (CTL) in P9 oil, CTL + chlorpyrifos in P9 oil, or CTL in xylene were conditioned by evaporative aging at 40° C for 4 weeks and exposed to termite attack in a modified ASTM D3345 4-week laboratory test. Actual CTL retentions were assayed post-test by X-ray fluorescence, and an approximate 50% decrease in CTL concentration found from the pretest nominal CTL retentions. With all three treatments, termite feeding on wood with actual retentions of 0.05-0.10 pcf (corresponding to 0.10-0.21 pcf nominal) did not differ significantly from the respective solvent controls. CTL retentions of 0.13-0.15 pcf (0.41-0.45 pcf nominal) limited wood weight loss from termite feeding to 6-13%, and retentions of 0.26-0.39 pcf (0.81-0.94 pcf nominal) CTL resulted in only 3-4% wood weight loss. Termite mortality was correlated with CTL retention. These results demonstrate that chlorothalonil is toxic to termites, and at the appropriate retention will deter Coptotermes formosanus from feeding on treated wood.

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