|Abstract or Summary
- A root-lesion nematode, Pratvlenchus penetrans, was determined to
be a major component of peppermint stand decline in Western Oregon.
Regression analysis showed that P. penetrans root densities in August
were negatively correlated (P=0.01) with yield, while soil densities
in August and root and soil densities in April were poorly correlated
with yield. Multiple regression analysis showed that soil texture,
stand vigor, and nematode root densities accounted for 80% (R² =0.80)
of yield variability. Additional parameters; ectoparsitic nematode
densities, soil pH, soil bulk density, and soluble solids did not
improve regression models.
Seasonal population dynamics studies demonstrated that root
population densities increased in late March and peaked in mid-May.
Soil populations peaked in spring before root populations and in the
fall as nematodes emigrated from senescent roots. Root and soil
populations declined to lowest densities in late winter. Seasonal
distribution studies indicated that populations did not migrate
vertically and the recommended depth of 15-20 cm was adequate for
sampling nematodes throughout the year.
Greenhouse studies demonstrated that Murray Mitcham was most
susceptible, Todd Mitcham was intermediate, and Black Mitcham was most
tolerant to P. penetrans injury. Murray Mitcham supported lower
nematode reproduction and exhibited greatest root necrosis. In a
two-season study, Black and Todd Mitcham were not damaged during the
first season, while Murray Mitcham plants exhibited significant top
and root stunting. All cultivars were damaged during the second
Soil texture modified population dynamics in greenhouse pot
cultures. Nematode density increased faster in Camas gravelly sandy
loam than in either Newberg loam or Cloquato silt loam. Plant top
biomass was not influenced by soil texture and nematode inoculation.
However, root biomass was significantly reduced with
nematode-inoculated plants in the loam and gravelly sandy loam, but
not in the silt loam.
Carbamate nematicides were evaluated for managing P. penetrans
damage of peppermint. Oxamyl at 0.6-16.5 kg a.i/ha produced
significant yield responses. Early spring applications enhance plant
growth, while fall and summer treatments were ineffective. Oxamyl
applications of 1.1-2.2 kg a.i./ha 5 to 10 days before spring flaming
are recommended. Management guidelines based on soil texture, stand
vigor, and nematode densities were developed for oxamyl treatments.