SOYBEAN MATURITY GROUP AND PLANTING DATE EFFECTS ON SEED YIELD AND POPULATION-DENSITIES OF HETERODERA-GLYCINES

The effects of planting date and soybean maturity group on population densities of Heterodera glycines, the soybean cyst nematode (SCN), and soybean yield in the presence of this pathogen were determined in two series of factorial experiments. The first series of experiments eval uated May- versus June-planted soybean of mio maturity groups (V and V II-early vs late maturity) with and without nematicide treatments at f our North Carolina locations (environments) in 1986 and 1987. The seco nd series of experiments concerned three planting dates (April, May an d June) with four soybean maturity groups (IV-VII) at a total of six l ocations between 1989-1992. Delayed soybean planting resulted in a sig nificant (P less than or equal to 0.05) reduction in the initial popul ation density (Pi) of SCN. The effects of planting date on final popul ation densities (Pf) of SCN were usually significant, but not predicta bly so. Environmental differences associated with locations and planti ng date likely account for the significantly higher or lower Pf. Late- maturing soybean cultivars consistently resulted in greater SCN Pf at season's end than did early maturing cultivars (P=0.0001). Soybean yie lds were increased by nematicides in early plantings (P=0.05), but not in late plantings, probably a result of the attrition of SCN Pi in re sponse to late planting. Mid-May planted soybean yields generally were the greatest of all planting dates.