Planting Date and Soybean Cultivar Maturity Group Affect Population Dynamics of Heterodera glycines, and All Affect Yield of Soybean.

Five soybean cultivars, one each from Maturity Groups (MG) III, IV, V, VI, and VII, all susceptible to Heterodera glycines, were planted in H. glycines-infested soil in April, May, June, and July at multiple locations in Arkansas and Missouri. The purpose of the study was to determine whether planting early reduces yield losses due to H. glycines. The population levels of cysts, eggs, and secondstage juveniles of H. glycines were determined from soil samples collected at planting and harvest. Yields were measured from the two middle rows of 4.9 or 6.1-m four-row plots. The population dynamics of the nematode varied with planting date, cultivar, MG, and initial nematode population. Generally, the lowest reproductive factor (Rf = final population/initial population) for any year was on the MG III cultivar, regardless of planting date or field location. Also, the Rf was generally lower on each cultivar planted in April than in June or July. The highest Rf values were on cultivars in MG VI or VII planted in June or July. Yields were not consistently correlated with initial nematode population level. Early planting of late-maturing soybean cultivars may be profitable, but early planting of MG III cultivars, though supporting little if any increase in nematode numbers, did not result in high yields.