Horizontal and Vertical Distribution of Longidorus africanus in a Bermudagrass Field in the Imperial Valley,...

The horizontal and vertical distribution of the needle nematode Longidorus africanus was studied in a bermudagrass field in the Imperial Valley in southern California. A geostatistical method involving the use of semi-variograms was used to quantify the relationship between sampling distance and variation in L. africanus population levels. Semi-variance between nematode numbers from different samples was very low when samples were taken close together, increased with sampling distances up to ca. 15 m, and fluctuated around a sill value at distances greater than 15 m. At very large sampling distances the semi-variance increased further. It was concluded that patches with fairly similar numbers of L. africanus were elongated and up to 15 m long. Seasonal fluctuations over a 2-year period, in total numbers of L. africanus extracted from three depths, were large and highly correlated with soil temperature. Population densities were greatest during the summer months and lowest during the winter. Averaged over the 2-year period, L. africanus population densities increased with increasing depth. Chances for detecting this nematode are greatest in summer at depths of 60 to 90 cm.