Spatial distribution of Heterodera trifolii in Chinese cabbage fields

Although Heterodera trifolii is commonly known as the clover cyst nematode, recently the nematode has been identified as a serious menace for Chinese cabbage growers in highland areas in Korea. Soil samples were collected from two Chinese cabbage fields highly infested with H. trifolii in highland areas of Korea, Jungsun and Samcheok, in 2014 and 2015, respectively. A total of 777 (2 × 2 m sampling area) and 414 (5 × 5 m area) soil samples were collected from Jungsun and Samcheok, respectively. The total cysts, cysts with eggs, number of eggs, and empty cysts were calculated for each sample. Distribution patterns for these variables were characterized using spatial analysis by distance indices (SADIE) and variogram model analysis. The aggregation index for cysts with eggs was higher in Jungsun (89.32) than Samcheok (3.63), which indicated that the cyst population density was higher. However, the spatial association of total cysts versus cysts with eggs was higher in Samcheok. The Gaussian model showed reasonable independent range of the nematode in Jungsun and Samcheok to be approximately 53.66 m and 48.54 m, respectively. The model suggested that each nematode sample should be taken at least 50 m apart in the given areas. Inclusion of this distribution pattern may significantly minimize the number of samples in future sampling methods, which could save time and labor, and initiate management practices by elucidating spatial variability factors that influence crop yield.