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Rootlesion nematode population cycles (total population in soil and roots) also follow behind root growth dynamics, with peaks and lows occurring four to six weeks after those for roots (see Figures above). This time interval is the approximate time it takes for P. penetrans to complete one generation and may explain the lag in response of nematodes behind that observed for roots. This pattern occurs with nematicide treatment as well. However, root peaks are larger and nematode peaks are suppressed.
Rootlesion nematodes are migratory endoparasites that may occur in soil, roots and rhizomes. Figure 1 above illustrates how the proportion of the population in each of these three habitats changes through the year. This figure is the composite of two years of data from each of two field sites and clearly describes the seasonal distribution of nematodes in these different habitats. While rootlesion nematodes infect rhizomes, which may be important in spreading this pathogen to other fields, the proportion of the total population in the rhizomes is very small and can be ignored in the overall dynamics of the whole population. The most important point from Figure 1 is that substantial proportions of the population may be found in the roots and in the soil and that the proportions in these two habitats vary through the year. In very early spring, the majority of the population is in the roots. Conversely, in the fall a larger part of the population is in the soil. Therefore, to census the total population accurately, both soil and roots need to be sampled at the same time regardless of when samples are taken. 