pdf, 57.71Mb - Entomological Society of Canada

108 A. K. Watson and P. Harris
Table 21
Table 22
Recovery of P./Jicridis Kirj. & Ivan. on Russian knapweed, A. repem (L.) DC., at the
Regina Research Station.
Precipitation
Year Galls/m: P. picridislm: A. repetls stems/m: September-May (mm)
1977 0
1978 0.67
1979 3.0
1980 no obvious
galls but some
swollen stems
1981 0.63
0
2.9
3599
16
15.0
52.0
18.6
167.5
212.5
213.0
145.7
108.6
The nematode population declined in the springs of 1980 and 1981, which was likely the
result of the dry conditions. In the five years from release, no P. picridis were found in the
control strip of knapweed planted 3 m away from the test plots.
At the Ste-Anne-de-Bellevue site, 6 m l plots were established in the early spring of
1977 and 100 000 nematodeslm l were inoculated in three of the plots. Russian knapweed
was transplanted into all plots and eight crop species were sown in rows between the
Russian knapweed plants in 1977. In 1978. globe artichoke and safflower were sown in
all plots. A few nematode galls were observed on Russian knapweed in 1977 and heavy
galling occurred on Russian knapweed in 1978, 1979, and 1980. In 1981, gall formation on
Russian knapweed was reduced. Galls did not develop on any of the tcst plant species in
1977, 1978, or 1979.
Effect of P. picridis Otl the ktlapweed
P. picridis was innoculated into 3 m l plots of pure Russian knapweed at Jenner, Alberta.
at a rate of 30 Ooo/ml, and three control plots were established with a 50 em buffer zone
from the treated area.
No galls were found on the knapweed in the 1978 growing season even though the
nematodes had been kept in soil for six weeks before release. However, in the spring of
1979, most of the knapweed shoots in the treated plots were galled, although those
appearing later in the summer were not infected. The plots were sampled at the end ofthe
growing season, the knapweed counted. weighed, and the nematodes extraced (Table
22). The results show that, apart from distorting the knapweed stems, the nematode had a
negligible effect. This is in contrast to the results reported from the USSR (Kovalev et 01.
1973). The other notable feature about the results is that in spite of the close proximity of
the treated and control plots, there had been little movement of the nematode into the
control plots.
This trial was terminated at the end of 1979, as the knapweed on the surrounding area
has been treated with glyphosate and apparently eliminated.
Effect of P. picridis Kirj. & Ivan. on A. repetls (L.) DC. at Jenner, Alberta in 1979.
No. stems! No. seed headsl Dry weight of No. nematodes!
Treatment 0.25 ml 0.25 m l fohage/0.25 m l 0.25 m:
P. picridis 25.3 ± 3.9 73 ± 20.7 42 ± 6.2 2259 ± 163
Control 33.2 ± 4.3 55 ± 16.0 44.8 ± 7.0 5.7 ± 3.9