ALLELOCHEMICALS FOR CONTROL OF PLANT-PARASITIC NEMATODES .1. IN-VIVO NEMATOCIDAL EFFICACY OF THYMOL AND THYMOL BENZALDEHYDE COMBINATIONS/

Greenhouse experiments were conducted to evaluate the nematicidal acti vity of thymol, a phenolic monoterpene present in the essential oils o f several plant families. Thymol was added to soil at rates of 25-250 ppm. Initial and final population densities of Meloidogyne arenaria, H eterodena 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 alde hyde present in nature as a moiety of plant cyanogenic glucosides. Com binations in which benzaldehyde was applied at 100 ppm showed synergis tic effects in suppressing initial and final soil populations of M. ar enaria and H glycines. Significant reductions in root galling and cyst formation on soybean were attributable to thymol at greater than or e qual to 50 ppm.