Soybean maturity group and planting date effects on seed yield and population densities of Heœrodera glycines (1)

Summary - The effects of planting date and soybean maturity group on population densities of Helerodem glycines, the soybean cyst nematode (SCN), and soybean yield in the presence of this pathogen were derermined in two series of factorial experiments. The first series of experiments evaluated May- versus June-planted soybean of IWO maturity groups (V and vn - early vs la te maturity) with and without nematicide treatments at four North Carolina locations (environments) in 1986 and 1987. The second series of experiments concerned three planting dates (April, May and June) with four soybean maturity groups (lV-VII) at a total of six locations between 1989-1992. Delayed soybean planting resulted in a significant (P:s 0.05) reduction in the initial population density (Pi) of SCN. The effects of planting date on final population densities (Pf) of SCN were usually significant, but not predictably so. Environmental differences associated with locations and planting date likely account for the significantly higher or Jower Pf Late-maturing soybean cultivars consistently resulted in greater SCN Pfat season's end than did early maturing cultivars (P =0.0001). Soybean yields were increased by nematicides in early plantings (P =0.05), but not in lare plantings, probably a result of the attrition of SCN Pi in response to lare planting. Mid-May planted soybean yields generally were the greatest of ail planting dates.