physicochemical

EFFECT OF WEED MANAGEMENT PRACTICES ON WEED CONTROL
significantly reduced the weed density as compared
to unweeded control (Table 1). Maximum density of
42.2 weeds m -2 as recorded in 2003 and 49.1 m -2 in
2004 in the weedy check. They were reduced to a
minimum of 5.2 and 9.6 m -2 with weed control
efficiency of 80 and 88 per cent in the corresponding
years due to hand weeding at 15,30,45 and 60 days
after transplanting. The herbicides oxyflourfen @ 0.15
kg ai ha -1 and oxydiargyl @ 0.1 kg ai ha -1 applied
on third day after transplanting of onion significantly
reduced the density of weeds. The weed control
efficiency of these herbicides was 31.5 to 37.7 and
28.4 to 35.4% respectively. Applicaton of
pendimethalin @ 1.0 kg ai ha -1 did not reduce the
density of weeds significantly compared to the weedy
check. Application of pendimethalin @ 1.0 kg ai
ha -1 followed by hand weeding at 45 days after
transplanting significantly reduced the density of
weeds compared with herbicide alone during 2003
and 2004. The weed control efficiency was 54.5 per
cent and 59.9 per cent in the two years. Integration
of herbicides with one hand weeding at 45 days after
transplanting was found to be effective in reducing
weed density over sole application of herbicides.
Among the integrated treatments, oxadiargyl @ 0.1kg
ai ha -1 followed by hand weeding at 45 days after
transplanting recorded the highest weed control
efficiency of 59 per cent, closely followed by
pendimethalin @ 1.0 kg ai ha -1 + hand weeding at 45
days after transplanting. However, none of the
integrated treatments could reach the level of weed
free treatment (84%).
Effect on onion crop:
The results showed that 96-99% of the onion
seedlings survived in different weed management
treatments, indicating that the herbicides had no
phytotoxicity (Table1). The growth of onion was
severely affected in the weedy check. The plant
height, number of leaves per plant and pseudo stem
diameter were significantly reduced due to severe
competition for resources owing to significant
reduction in weed density in the weed free check.
The plant height and number of leaves per plant
increased two fold than in the weedy check in both
the years. The pseudo stem diameter also improved
significantly. These results are in conformity with the
findings of Kewat et al (2006) and Warade et al
(2006).The herbicide sprays were less effective than
hand weeding. The plant height, number of leaves
per plant and pseudo stem diameter of onion were
significantly reduced (Table 2). However, the
integrated weed management comprising spray of
any one of these three herbicides followed by hand
weeding at 45 days after transplanting enabled the
crop to produce the number of leaves on par with
hand weeded check. Hand weeding at 15, 30, 45 and
60 days after transplanting of onion was the most
effective (Table3) in terms of increased diameter and
weight of the bulbs significantly compared to the
weedy check. The bulb yield increased from 123 q
ha -1 in 2003 and 116 q ha -1 in 2004 in the weedy
check to 280 and 265 q ha -1 due to hand weeding
gaining an yield advantage of 128% during the two
years. Herbicide application either alone or integrated
with hand weeding at 45 days reduced the bulb
diameter and yield significantly compared to hand
weeding. The results are in accordance with those
reported by Kolhe (2001).The integrated weed
management was significantly superior to the
corresponding herbicide treatment in improving the
diameter and weight of bulbs as well as yield during
both the years. The results are in accordance to those
reported by Kewat et al (2006). The higher yield in
these treatments was due to effective control of
weeds in the early stage by chemicals and at later
stages by hand weeding, which ultimately resulted
in increased crop growth and yield.
Economics of weed management
It is inferred that hand weeding at 15, 30,45
and 60 days after transplanting is the best weed
management practice to improve the crop growth,
yield components and yield of onion and recorded
the highest benefit cost ratio. If labour scarcity is
acute, spraying oxyflourfen @ 0.15 kg ai ha -1 or
oxydiargyl @ 0.1 kg ai ha -1 or pendimethalin @ 1.0
kg ai ha -1 three days after transplanting, followed by
hand weeding 45 days after transplanting is the best
weed management strategy rather than herbicide
spray alone.
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