Comparison of extraction techniques and augers of different size.

Because of differences in winter survival of Pratylenchus penetrans after different host plants, concern arose about traditional extraction and soil sampling techniques. Possible bottlenecks are a too short incubation period of the root material for the time of year, or an auger size to small to pick up tough, fresh, root material. Two experiments were carried out to compare different auger sizes and variations on the standard Oostenbrink elutriation technique with additional filter-incubation of the organic material left on the top sieve (180 microns) of the elutriator. The hypothesis that soil sampling in a green crop results in more root material with a 2.5-cm auger, compared to a 1.3 cm auger, proved to be right. Since there was no effect on the number of P. penetrans recovered, the 1.3 cm auger is preferred because with this auger more cores are taken to gather the same amount of soil, resulting in a better estimation of the population. It appeared that highest yields are accomplished with the standard extraction-plus incubation-method described above. Every methodical effort to improve the extraction effectivity, caused only loss of nematodes. An incubation period of two weeks came out to be minimum. After this period, another 15 to 20% of nematodes could be harvested.