MSc

A field experiment was conducted at the Instructional Farm, College of
Agriculture, Vellayani, Thiruvananthapuram to evolve a suitable integrated
weed management practice for upland rice. The study was conducted during
the virippu season of 1999.
The field experiment was laid out in split plot design having three
replication with three main plot treatments and six subplot treatments. Three
different spacings i.e., 15 x 10 cm 15 x 10 cm, 20 x 10 cm and 20 x 15 cm
were the main plot treatments. Sub plot treatments were different weed
management strategies consisting of three different herbicides in combination
with one hand weeding, hand weeding alone twice, unweeded check and weed
free check. Pendimethalin, Fluchloralin and Butachlor were the herbicides
used in the experiment. The rice variety used for the experiment was Matta
Triveni.
The results of the study revealed that grasses, broadleaved weeds and
sedges competed with the rice crop. Different weed management practices
included in this experiment significantly influenced the intensity and
distribution of the weeds, but the fluchloralin treatment (W2) resulted in
phytotoxicity and affected the crop stand considerably.
The application of butachlor + one hand weeding at three weeks after
sowing (W3) and pendimethalin + one hand weeding at three weeks after
sowing (wj ) showed very high control over weeds throughout the crop growth
period. The plots hand weeded twice at 20 and 40 days after sowing also

registered considerable reduction in weed growth. Among the spacings tried
the medium spacing of 20 x 10 cm (S2) resulted in lowest absolute density of
weeds. Although the application of Pendimethalin and Butachlor resulted in
good control of grasses and broadleaved weed, their effect on sedges was
meagre.
All the weed management treatments except fluchloralin (W2) resulted
in improved yield attributes and significantly higher yield compared to weedy
check. Weed free check (S6) recorded the highest grain yield. Unweeded
check recorded the lowest with 49.14 per cent yield reduction compared to
weed free check. The various spacings tried did not result in significant
difference in yield. No herbicide used in this experiment resulted in residual
toxicity after the cropping season.
Pendimethalin @ 1.5 kg a.i. ha-' + one hand weeding three weeks after
sowing (w,) and Butachlor @ ] .25 kga.i. ha-' + one hand weeding three
weeks after sowing (W3) were the most remunerative treatment and keeping
the field weed free during the entire crop growth period was found to be not
economic.