- The efficiencies of wet sieving/sucrose
centrifugation (WS/SC) recovery of Pratylenchus penetrans
(59 %), Paratylenchus sp., (80 %), and Criconemella
xenoplax (66 %) were established. Baermann funnels (BF)
recovered significantly more P. penetrans (p = 0.01) and
significantly less (p = 0.01) C. xenoplax than did WS/SC.
While densities of P. penetrans in stored soil remained
constant over the three days following field sample
collection, Paratylenchus sp. and C. xenoplax densities
increased significantly on the second day and decreased to
their original level on the third day. During mist
chamber extraction, P. penetrans continued to emerge from
peppermint root tissue for 38 days, but 90 % of the total
was recovered after 10 days.
The standard core, consisting of 500 g dry soil plus
the roots and rhizomes in that soil, was developed to
express endoparasitic and ectoparasitic nematode densities
in peppermint field soil, roots, and rhizomes.
Enumerating nematode densities within the different plantsoil
components of a particular volume of soil more
closely describes the total nematode population pressure
on the plant growing in that volume of soil. Therefore,
endoparasitic nematode population levels were expressed as
numbers in standard core soil, roots, rhizomes, or total
core (soil, root, and rhizome populations combined).
P. penetrans populations in peppermint fields peaked
in early May, decreased through the summer, peaked again
in August, and decreased through the fall to a low winter
level. Peaks in the P. penetrans population followed
peppermint root weight peaks by 3 to 6 wks. Paratylenchus
sp. populations remained at relatively low levels
throughout the year except for a pronounced peak in
August, which followed the root weight peak by 3 to 6 wks.
The C. xenoplax population also peaked 3 to 6 wks after
the August root weight peak but fluctuated markedly
throughout the remainder of the year. From 70 to 90 % of
the total P. penetrans population was in roots in early
May, decreased to 40 to 50 % by late June and 20 to 40 %
in August. Up to 20 % of the population was in rhizomes
on some dates, but the rhizome percentage was usually less
than 10. Fewer P. penetrans were recovered from rhizomes
during the harsh winter of 1988-89 than during the mild
winter of 1989-90.
Analysis of point samples (pretreatment,
posttreatment, and harvest samples) and area under
nematode population curves (AUNPC) were used to compare
nematode populations in oxamyl-treated (1.1 kg a.i./ha)
and nontreated plots in two peppermint fields through the
two growing seasons. Point sample analyses detected
significant decreases in treated soil, root, and total
standard core P. benetrans populations compared to
nontreated populations in several pretreatment and harvest
sample dates and in two rhizome harvest sample dates. No
treatment differences were observed in Paratylenchus sp.
or C. xenoplax populations using this analysis. AUNPC
analysis detected significant decreases in several treated
root and rhizome P. penetrans populations compared to
nontreated populations and in total core populations in
field 1 during one growing season and in field 2 during
two growing seasons. Significant decreases in C. xenoplax
populations were observed in one field during one growing
Peppermint hay weight was significantly greater in
treated than in nontreated plots in one of three fields in
1988 and in one of three fields during 1989. Oil in ml/kg
fresh hay weight was significantly lower in treated than
in nontreated plots in one of three fields during 1989.
No treatment differences were detected in milliliters of
oil distilled from 2m² field area.
Peppermint oil production is the final measure of a
treatment from a mint grower's perspective. Because
oxamyl had no effect on mint oil production, AUNPC appears
to be a better measure of parasitic nematode pressure on
peppermint, since this method of analysis detected fewer
significant differences between nematode populations
between treated and non-treated plots.