Effects of Wheat and Soybean Planting Date on Heterodera glycines Population Dynamics and Soybean Yield with Conventional Tillage. S. R. Koenning, Former Research Associate, Department of Agronomy, University of Missouri, Columbia, Delta Center, P.O. Box 160, Portageville, MO 63873. S. C. Anand, Professor of Agronomy, Department of Agronomy, University of Missouri, Columbia, Delta Center, P.O. Box 160, Portageville, MO 63873. Plant Dis. 75:301-304. Accepted for publication 27 September 1990. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/PD-75-0301.

The influence of winter wheat (Triticum aestivum) cover crop vs. winter fallow and of soybean (Glycine max) planting date on the population dynamics of soybean cyst nematode (Heterodera glycines) (SCN) was determined during a 2-yr period. Numbers of SCN cysts, eggs, and second-stage juveniles were unaffected by wheat as opposed to winter fallow. Delay in soybean planting associated with double-cropping wheat, however, allowed for a significant decline in the numbers of SCN between early May and late June. Midseason densities of early May soybean plantings were greater than those of mid-June to late June plantings. Soybean yields were greater with a late May planting than with either early May or late June plantings in 1985. Late soybean plantings tended to have greater densities of SCN eggs at soybean maturity, probably a result of less SCN damage in these plots. Neither soybean planting date nor wheat affected soybean yields in 1986. Delayed soybean planting may reduce the damage potential of SCN by reducing inoculum density at planting, but wheat has no direct effect on SCN.