Abstract
Gavassoni, W.L., G.P. Munkvold, and G.L. Tylka. 1996. Spatial difference of soybean cyst nematode cyst and egg populations. Phytopathology 86 (supplement):86.
The spatial patterns, dissemination, and population densities of soybean cyst nematode (SCN), Heterodera glycines, were studied in naturally infested fields in central and northcentral Iowa in 1994 and 1995. At each location there were 4 plots of 15.25 x 30.50 m subjected to different tillage treatments. Soil samples were taken in a 1.14 m grid and processed to extract cysts; eggs were subsequently extracted from cysts. Cysts and eggs were counted and the data analyzed using geostatistics. Semivariances of the cyst data were smaller and more regular than semivariances of the egg data. Some semivariograms did not fit well to any standard model; most were best described by a spherical model and some by a linear model. Tillage operations, conducted 8 months after the initial sampling, resulted in dramatic changes in semivariogram shape. However, semivariograms changed only slightly in plots receiving no tillage or reduced tillage. Tillage may disrupt spatial dependence of soybean cyst nematode populations, resulting in more random or more uniform spatial patterns.