A Spatial Analysis of the Potato Cyst Nematode Globodera pallida in Idaho

The potato cyst nematode Globodera pallida is a globally regulated and quarantine potato pest. It was detected for the first time in the United States in the state of Idaho in 2006. A spatial analysis was performed to (i) understand the spatial arrangement of fields infested with G. pallida in southern Idaho using spatial point pattern analysis, and (ii) evaluate the potential threat of G. pallida for entry to new areas using spatial interpolation techniques. Data point locations, cyst numbers and egg viability values for each infested field were collected by USDA-APHIS during 2006 to 2014. Results showed the presence of spatially clustered fields infested with G. pallida (P = 0.003). We determined that the spread of G. pallida grew in diameter from the original center of infestation toward the southwest as an ellipsoidal-shaped cluster. Based on the aggregated spatial pattern of distribution, we determined that G. pallida spread followed a contagion effect scenario, where nearby infested fields contributed to the infestation of new fields, probably through soil contaminated agricultural equipment or tubers. We determined that the presence of G. pallida in southern Idaho is unlikely to be associated with new introductions from outside the state of Idaho. The aggregation pattern of fields infested with G. pallida, with an average of 4,263 cysts/ha and egg viability of 25%, facilitates quarantine activities and confines the propagation of this pest to a small area, which in 2017 was estimated to be 1,233 ha. The tools and methods provided in this study facilitate comprehensive approaches to improve G. pallida control and eradication programs as well as to raise public awareness of the problems surrounding this economically important potato pest.