Abstract:
Fluctuations in population density of Pratylenchus sp.,
Trichodorus sp., and Xiphinema americanum s. 1. in three blueberry
fields were determined monthly for one year. Pratylenchus densities
were greatest in August and least in October. Three distinct
periods of population growth occurred; during January, April, and
between June and August. Trichodorus populations were highest
between February and April, and lowest in June. Xiphinema occurred
in only one of three fields sampled, with densities highest in
May and lowest in August.
Root samples from blueberry plants, and soil samples from
the rooting zone were taken in June of 1986 to determine horizontal
and vertical distribution of Pratylenchus and Trichodorus
populations. Samples were taken at depths of 0-3, 3-9, and 9-15
inches at 6-18 and 18-30 inches from the base of the plant and
within and between rows.
Pratylenchus densities at certain orientations depended on
the distance from the base of the plant that the soil was sampled.
Samples taken within the row were similar at one and two feet
from the base of the plant, whereas samples from between rows
taken at one foot from the base of the plant were significantly
less (22%, p< .10) than those taken from two feet away. The
presence of a living mulch between the rows may account for this
difference.
Pratylenchus populations differed significantly with depth.
There was little difference in density between 3-9 inches and 9-15
inches, but both differed significantly (p<0.01) from 0-3 inches.
Densities were greatest below 3 inches.
Trichodorus densities depended on the distance the sample was
taken from the base of the plant. At one foot from the base of
the plant, the population was significantly greater (p< .01) than
at two feet.
The horizontal distribution of Pratylenchus and Trichodorus
in a blueberry field was determined by sampling five rows of ten
plants each, at a depth of 3-9 inches. Pratylenchus populations
tended to be distributed in a clumped pattern. The mean population
density of 50 samples was 270 Pratylenchus/ qt. soil and
42% of the 50 plants sampled were infested. In contrast,
Trichodorus distribution was fairly uniform, with 74% of the 50
plants infested. The mean population was 253 Trichodorus /qt.
soil.
Efficacy trials with fenamiphos (Nemacur 3E) indicated that
the most effective rate for Pratylenchus control was 12 lbs. ai/A,
which reduced populations by 95%. Fenamiphos was not an effective
control for Trichodorus in this study.
Analysis of fenamiphos treated fruit from two Oregon and one
Washington blueberry fields showed no detectable chemical residues
for 6 or 12 ai/A rates at the spiking level of 0.1 ppm.
