New sampling method to detect low populations of Globodera rostochiensis and G. pallida
A new sampling method to detect low populations densities of Globodera rostochiensis and G. pallida (EPPO A2 quarantine pests) has been developed in the Netherlands. With this method it is possible to detect small infestations with a predefined probability, and therefore to take better decisions on the nature and extent of control measures, as the final aim is to reduce the use of nematicides.
Analysis of intensive sampling data from 40 patchy infestations representing all growing areas in the Netherlands provided a model of distribution (simple exponential model) describing expected cyst numbers within infestations. The authors then defined a standard focus with a central population density of 50 cysts/kg of soil which should be detected with a probability of 90 %, and used a special computer programme to simulate sampling procedures in order to define an optimal sampling grid. As a result, grid dimensions near 5 x 5 m with a core size of 52 g (sample size 6.9 kg/0.33 ha) were recommended as being the best compromise between the two following conflicting aims: to minimize sample size and variance of detection probability, and to minimize time needed to collect and process the samples. When compared with the statutory soil sampling procedure still used in the Netherlands of 7.5 x 7.5 m grid and core size of 3.3 g (sample size of 200 g/0.33 ha), and with an average detection probability of 90 %, the new sampling method detects foci with central densities a hundred times smaller, and costs only 3-4 times as much to perform. The new method can detect foci with a central density of 150 cysts/kg soil. ;The authors noted that practical problems created by a more intensive sampling procedure can be solved by using automated sampling devices mounted on a jeep and elutriators for the extraction of cysts from soil samples of up to 3 kg.
The authors concluded that with this new sampling procedure, it has been possible to reduce very significantly (80 to 90 %) the use of soil fumigants in seed and ware potato-growing areas in the Netherlands.
Sources
Been, T.H.; Schomaker, C.H. (1996) A new sampling method for the detection of low population densities of potato cyst nematodes (Globodera pallida and G. rostochiensis).
Crop Protection, 15(4), 375-382.