Abstract:

The influence of cultural practices (intercropping, time of planting, spacing,
time of harvesting) and use of botanicals and synthetic insecticide in field
management of the major flower, pod and seed pests of pigeonpea were
investigated during the first and second rains of 1998 and the first rains of
1999 at Kawanda Agricultural Research Institute (KARI).
The effects of intercropping on the incidence and/or severity and damage of
flower beetles (Mylabris spp.), thrips (Megalurothrips spp.), pod borers
(Helicoverpa armigera), pod bugs (Clavigralla spp.), pod fly (Melanagromyza
spp.) and bruchids (Callosobruchus spp.) on pigeonpea were studied. Six
treatments Viz.(short duration pigeonpea intercropped with finger millet,
medium duration pigeonpea intercropped with finger millet, short duration
pigeonpea intercropped with cowpea, medium duration pigeonpea
intercropped with cowpea, short duration pigeonpea sole crop and medium
duration pigeonpea sole crop) were imposed. The experiment was laid out in
a randomised complete block design (RCBD) on 6x4m plots and replicated
four times.
Similarly, the effects of time of planting and spacing on the above parameters
and pests was studied, being laid out in a split plot design, arranged in a
RCBD. Three planting dates at on-set of rains, 2 and 4 weeks after on-set of
rains were in the main plots (14x11m) and three spacing treatments as
50x20cm (recommended), 25x1 Ocm and 100x40cm) in the sub plots (4x3m),
and replicated four times. Effects of time of harvest on pigeonpea seed
damage in storage was also evaluated, with three treatments (at physiological
maturity (PM), 2 and 4 weeks after PM), replicated four times in a RCBD.
Additionally, the effects of selected botanicals and a synthetic insecticide on
pigeonpea seed damage in storage was investigated using nine treatment
applications (4 fresh formulations of crude water extracts of ash, tobacco,
tephrosia and melia seed(MS); 2 fermented formulations of tephrosia and MS;
1 compound extract of tephrosia and MS; 1 treatment of cypermethrin
(synthetic) and the control). The experiment was arranged in a RCBD, on
4x3m plots, replicated four times. Data were analysed by M-STATC statistical
package except for time of planting and spacing which was by SAS system
for mixed models.
Results indicated that Mylabris pastulata, H. armigera and C. chinensis
infestations were significantly lower (p<0.05) in pigeonpea intercropped with
millet than in either pigeonpea intercropped with cowpea or pigeonpea sole
crops. But infestations of Megalurothrips sjostedti, Aphis spp and Clavigralla
spp were significantly lower (p<0.05) in pigeonpea intercropped with cowpea
than in either pigeonpea intercropped with millet or pigeonpea sole crops.
Seed damage by Clavigralla spp and H. armigera were significantly lower in
pigeonpea intercropped with cowpea than in pigeonpea intercropped with
millet or pigeonpea sole crops. Intercropping did not significantly influence
pigeonpea seed damage by Melanagromyza spp. Seed damage by pod bugs
was highest (17.0%-19.1%) followed by pod borer damage (4.3%-7.1%) and
pod fly damage was the lowest (0.9%-1.6%).
Planting date but not spacing significantly (p<0.05) influenced damage by H.
armigera, Clavigralla spp, Melanagromyza spp and C. chinensis. Planting at
on-set and 2 weeks after on-set of rains significantly reduced damage on
pigeonpea seed. The interaction of planting date and spacing were significant
only for Clavigralla spp in the first rains of 1999 and C. chinensis in both
rains.
Seeds harvested at physiological maturity and 2 weeks after physiological '
maturity, had significantly lower damage in storage than those harvested at 4
weeks after physiological maturity. The adult C. chinensis emergence from
seeds after one and two months of storage and the seed damage were
highest from treatments with ash and the control, while the lowest were in
seeds from plots treated with cypermethrin and tobacco. The performance of
tephrosia and melia seed extract (MSE) followed those of cypermethrin and
tobacco. However, the fermented extracts of tephrosia and MSE were more
effective in reducing adult emergence and seed damage compared to their
fresh formulations.
Cypermethrin and crude extracts of tobacco, tephrosia and melia seed
significantly reduced field infestations and pigeonpea seed damage in
storage due to C. chinensis. Tobacco extract had the highest efficacy
followed by tephrosia and melia seed extract.
In conclusion this study has shown that intercropping pigeonpea with cowpea
can significantly reduce pigeonpea seed damage in the field due to
Clavigralla spp and H. armigera. Planting pigeonpea at on-set of rains up to 2
weeks after on set of rains, significantly reduces pigeonpea seed damage by
H. armigera, Clavigralla spp, Melanagromyza spp and C. chinensis.
Harvesting pigeonpea at physiological maturity and 2 weeks after,
significantly reduces pigeonpea seed damage in storage due to C. chinensis.