Weed and root lesion nematode population dynamics over a three-year crop rotation: Spatial distribution and temporal stability

Many pests (weeds, pathogens, insects, and others) are not uniformly distributed but are spatially aggregated (clustered) in agroecosystems. However, pest management thresholds and pest management strategies are typically implemented assuming a uniform pest distribution and do not account for the spatial distribution of pests. Research investigating pest population dynamics was conducted near Coloma, WI from 1998 to 2000. In 1998, two potato fields (42 and 53 ha) were evaluated for root lesion nematodes, weeds, early blight, Verticillium wilt, petiole nitrate levels, and yields. In 1999, two additional potato fields (32 ha) were similarly evaluated. Weeds, root lesion nematodes, and yields were reevaluated in subsequent rotational crops the following year. A uniform 0.5-ha. grid was established in each field and each grid point was georeferenced using a differential GPS unit. Each parameter was quantified at the georeferenced grid locations for each season. Geostatistical methods (variography and index of dispersion) were used to analyze pest dynamics, including spatial distribution. Spearman's rank correlation and interpolated maps were used to identify temporal stability of each pest and spatial interactions between pests and edaphic factors.; Mean root lesion nematode populations increased with each succession of the crop rotation (potato/corn/vegetable). Corn appeared to be more conducive to nematode population growth than potatoes. The root lesion nematode spatial distribution was variable by field, but some degree of aggregation was observed. In many cases, nematodes occurred near the tillage implement entry point in the field. Nematode densities were not highly correlated with potato yields, corn yields, soil moisture, or soil pH, but fields with high densities were consistently correlated to Verticillium wilt symptoms. Inter-season temporal stability was observed in each field. Based on root lesion nematodes' spatial distribution and temporal stability, the potential for site-specific management does exist.; Weed populations were generally spatially aggregated and were temporally stable within each field and crop. However, the level of spatial aggregation and temporal stability was dependent on weed management strategies, crop type, and crop health. Weed densities were not consistently correlated to crop yields. Weed population densities were typically below economic thresholds for the majority of the fields.