A handbbok on Weed Control in Rice.pdf

Nurseries
Seedling nurseries should be kept
weed free to prevent transplanting
grassy weeds along with rice. Weeds
in the nursery also compete with the
rice seedlings and can cause complete
nursery crop failure. Herbicide such
as thiobencarb, propanil, oxadiazon,
and butachlor can be used to control
weeds in the nursery.
Land preparation
Mechanical land preparation can
provide a weed-free field that is
optimal for early rice growth. The
land should be leveled after puddling
the soil. Unevenness in the field
results in areas of inadequate flood-
ing. Dikes, to contain and control an
undependable water supply, are
essential. In India, Sesbania aculeata
grown during the dry season as a
green manure crop is plowed in
before transplanting rice (Mukho-
padhyay 1983). This practice results
in less weed infestation in the main
rice crop.
Cultivar
Water depths largely determine the
type of rice grown. In general, mod-
ern semidwarf cultivars are grown in
shallow rainfed rice-growing areas.
In medium-deep rainfed rice-grow-
ing areas, tall cultivars that are
mostly photoperiod-sensitive are
grown.
Plant population
Close spacing, between 10 and 25 cm
in rows or hills, increases the ability
of rice plants to compete with weeds.
Rice should be transplanted in
straight rows to allow the use of
mechanical weeders.
84 Weed control handbook
Table 7.1. Herbicides suitable for use in transplanted rainfed lowland rice.
Herbicide
Bensulfuron
Bentazon
Butachlor
2,4-D or MCPA
Molinate
Oxadiazon
Oxyfluorfen
Pendimethalin
Piperophos +
dimethametryn
Piperophos + 2,4-D
Propanil
Quinclorac
Thiobencarb
Thiobencarb + 2,4-D
Rate
(kg ai/ha)
0.05
1.0-2.0
1.0
0.5-1.0
2.5-3.0
0.5-0.75
0.25
0.75
0.5
0.3 + 0.2
3.0-4.0
0.3
3.0
1.0 + 0.5
Water management
Keeping the rainfed lowland field
flooded after transplanting kills some
weeds and reduces the growth of
others. In most ricefields, continuous
flooding to a 5-cm depth is seldom
achieved because of problems in
regulating water depth and drainage.
With good land preparation and
good water control, weed problems
will be minimal. Other weed control
methods are necessary when rainfall
is not enough to provide continuous
flooding.
Comments and source of information
Apply 3-5 d after transplanting (DT)
(IRRI 1986).
Apply postemergence to control
broadleaf weeds and sedges. Weed
foliage must be exposed at application
(IRRI 1973).
Apply 3-6 DT (IRRI 1987).
Apply 3-4 wk after weed emergence to
control sedges, broadleaf, and aquatic
weeds. Lower water level to expose
foliage of small plants before spraying.
Also may be applied 4-5 DT
(IRRI 1973).
Apply 4-8 DT.
Apply 2-6 DT to control annual grasses
and broadleaf weeds (IRRI 1980).
Apply 4 DT (IRRI 1980, 1983, 1988a).
Apply preemergence about 6 DT to
control grasses and broadleaf weeds
(IRRI 1980).
Apply 2-5 DT to control annual grasses,
sedges, and broadleaf weeds
(COPR 1976).
Apply 2-8 DT to control grasses,
sedges, and broadleaf weeds
(IRRI 1986).
Apply postemergence to control
several grasses and broadleaf weeds
at the 2- to 3-leaf stage. Lower water
level of flooded fields about 24 h before
application to expose weed foliage
(COPR 1976).
Apply 3-5 DT (IRRI 1986).
Apply 5-8 DT. Water should be shallow
at application. Avoid draining or overflowing
for 3-5 d after herbicide application,
but do not expose soil surface
after treatment.
Apply about 5 DT (IRRI 1983).
Fertilizer
Nitrogen application should be timed
to provide the maximum benefit to
rice but the least benefit to the weeds.
Applying fertilizer to a rice crop with
poor weed control could be worse
than applying no fertilizer.