|Wyse Pester, D - COLORADO STATE UNIV.|
|Westra, P - COLORADO STATE UNIV.|
Submitted to: Journal of Nematology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 9, 2001
Publication Date: June 20, 2002
Citation: Wyse Pester, D.Y., Wiles, L., Westra, P. 2002. The potential for mapping nematode distributions for site-specific management. Journal of Nematology. 34(2):80-87 Interpretive Summary: Nematodes are microscopic worms in the soil that sometimes must be controlled with pesticides to prevent damage to crops. Often, the number of nematodes varies from location to location within a field so a grower may be able to minimize pesticide use if he or she had a map of nematode density within a field and applied pesticide only where there enough nematodes to justify the cost of the pesticide. Nematode density at a location is determined by the expensive process of extracting, identifying and counting the nematodes in a soil core. A map is made by estimating density throughout the field from densities determined at a limited number of locations. A map can be made only if there is some pattern to the variation in density within a field so that knowing nematode density at some locations provides enough information to estimate density at locations where cores were not collected. The nature of this pattern determines how many cores must be collected and analyzed to make a map for a field, and consequently, the cost of a map. We sampled nematodes in two irrigated corn fields for two years and observed that density within a field varied in a way that maps could be made. Moreover, the number of locations where nematode density must be determined to make a map may be small enough that growers can afford to determine if parts of the field may be left untreated.
Technical Abstract: The success of site-specific nematode management depends on a grower or advisor being able to afford to make a map of an infestation that is accurate enough for management decisions. The spatial dependence of nematode infestations and correlation of soil attributes with nematode density were assessed to investigate the scale of sampling required to obtain correlated observations of density and the use of soils data to reduce the cost of sampling. Nematodes and soil were sampled on a 76.2 by 76.2-m grid in two irrigated corn (Zea mays) fields for two years. Nematodes of each of three species were found in 36 to 77% of the cores from a field. Spatial dependence was detected for 10 of 16 distributions and 22 to 67% of the variation in density within a field could be attributed to spatial correlation. Density was correlated to distances of 115 to 649 m in the directions of 0, 45, 90 and 135º from the crop row and distances varied with direction. Correlations between nematode density and soil attributes were inconsistent between species and fields. These results indicate a potential for mapping nematode infestations for site-specific management, but provide no evidence for reducing the cost of sampling by substituting soils data for nematode counts when making a map.