Abstract
Gavassoni, W.L., G.P. Munkvold, and G.L. Tylka. 1998. Tillage alters spatial dependence of Heterodera glycines. Presentation at the 1998 Society of Nematologists Annual Meeting, St. Louis, MO.
The spatial patterns of Heterodera glycines were studied in two naturally infested soybean fields in Iowa from 1994 to 1997. At each location, there were 4 plots of 15.25 x 30.5 m subjected to different tillage treatments in the fall and spring. Soil samples (98 three-core samples per plot) were taken from a 7 x 14 grid (98 5.2 m2 contiguous quadrats) in the fall of 1994, before any tillage was performed and in the spring of the following years shortly after planting. Cysts were extracted from samples by elutriation and counted, then eggs were extracted from cysts and enumerated. The spatial patterns of cysts and eggs initially were aggregated, as indicated by Lloyd's index of patchiness and geostatistics. The range and sill for cyst densities, estimated from the spherical model, decreased in the plots after conventional tillage, but aggregation of the pathogen population did not change significantly in the absence of tillage.