Greenhouse experiments were conducted to evaluate the nematicidal activity of thymol, a phenolic monoterpene present in the essential oils of several plant families. Thymol was added to soil at rates of 25-250 ppm. Initial and final population densities of Meloidogyne arenaria, Heterodera glycines, Paratrichodorus minor, and Dorylaimoid nematodes, as well as disease incidence, declined sharply with increasing dosages of thymol. Thymol was also applied at 0, 50, 100, and 150 ppm to soil in combination with 0, 50, and 100 ppm benzaldehyde, an aromatic aldehyde present in nature as a moiety of plant cyanogenic glucosides. Combinations in which Benzaldehyde was applied at 100 ppm showed synergistic effects in suppressing initial and final soil populations of M. arenaria and H glycines. Significant reductions in root galling and cyst formation on soybean were attributable to thymol at 50 ppm.
