Effects of Soil Disturbance on Reproduction of Heterodera glycines.

Reproduction of the soybean cyst nematode (SCN), Heterodera glycines Ichinohe, on soybean, Glycine max (L.) Merr., has been compared in conventional till and no-till field plots. Rate of SCN population density increase during the growing season was lower in no-till than in conventional till plots (3,5), or the number of SCN at harvest was lower in no-till than in conventional till plots (6). In one study, there were no differences in numbers of SCN cysts between conventional till and no-till plots (1); only the number of SCN juveniles in July was significantly higher in singlecropped, conventional till soybeans than in soybeans double-cropped after wheat (conventional till and no-till). The objective of this study was to determine, in cores of disturbed and undisturbed soil, the number of SCN developing on soybeans grown in the greenhouse. Undisturbed soil cores were obtained by driving 15-cm-long segments of 10-cm-d plastic pipe into SCN-infested soil. In one experiment, cores were obtained on three dates from field plots following planting of soybeans no-till into wheat stubble in a Grenada silt loam soil. In another experiment, cores were collected in April 1985 from a field plot where soybeans had been p lanted following convent ional tillage practices in 1984. After collection, cores were randomly assigned to two treatments, disturbed and undisturbed. Cores were disturbed after removal from the pipe by