Heterodera glycines Invasion and Reproduction on Soybean Grown in Clay and Silt Loam Soils.

The soybean cyst nematode (SCN), Heterodera glycines Ichinohe, is a severe pest of soybean, Glycine max (L.) Merr., in the United States. Nematode reproduction and the seed yield losses caused by this nematode are influenced by soil texture (3,5,6). Todd and Pearson (5) recovered higher numbers of SCN females and cysts from a sandy loam soil than from silty loams. Soybean yield also has been negatively correlated with increasing sand content of a fine sandy loam soil (3). Young and Heatherly (6) repor ted six times more SCN cysts at seed harvest in a silt loam soil than in a clay soil. SCN population increased from planting to harvest in silt loam soil but declined significantly in clay soil (unpubl.). The clay content (58%) of Sharkey clay in this study was much higher than in soils cited in other studies. The study repor ted here describes tests to determine if the SCN population decline in the clay soil was due to lower juvenile invasion or lower nematode reproduction. Experiment I: Dry, uninfested Sharkey clay (8.5% sand, 34.0% silt, 57.5% clay; pH 6.6, 2.9% organic matter) and Dubbs silt loam (23.0% sand, 60.5% silt, 16.5% clay; pH 6.8, 1.3% organic matter) surface soils were passed through 6-mm-d hardware cloth, transferred to 7.5-cm-d pots, and thoroughly wetted for 2 days. Twenty-five hand-picked cysts collected from plants grown in SCN-infested soil for 40 days were added to the soil surface in each pot and