PIN NEMATODE POPULATION DYNAMICS

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Seasonal population cycles of pin nematodes from Central Oregon and the the Willamette Valley. Data were collected by taking cores to 4-6 inches, weighing the core and determining the number of nematodes that resided in 500 g of that soil.

Population dynamics of pin nematodes appear to differ between central Oregon and the Willamette Valley (see Figure above). Central Oregon populations decline between March and June while Willamette Valley populations remain at barely detectable levels through June. However, beginning in July, populations at both areas increase rapidly through October. Populations then decline again through the winter (not shown, Ingham, 1992). Pin nematode populations may respond to summer root growth as other species do (see Figure above) but may require warmer temperatures, which would explain the lack of an increase in numbers during the root flush in the spring. Furthermore, since pin nematodes are so small, they may not be as sensitive as other species to the decline in root biomass after harvest. Thus, populations continue to increase at a time when roots are declining. Since numbers can be very high during late fall and early winter when mint is dormant, these nematodes are speculated to be important in causing winter injury. This may be of particular importance in Central Oregon, where populations apparently remain higher through the winter.