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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.
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