A handbbok on Weed Control in Rice.pdf

Table 6.2. Herbicides suitable for use in irrigated rice direct seeded on puddled soil.
Herbicide
Bensulfuron
Bentazon
Bifenox + 2,4-D
Butachlor
Butralin
2,4-D or MCPA
Molinate
Oxadiazon
Quinclorac
Thiobencarb
Thiobencarb + 2,4-D
Rate
(kg ai/ha)
0.05
2.0
2.0 + 0.6
0.75
2.0
0.5-1.0
3.0
0.75-1.0
Oxyfluorfen
0.15-0.25
Pendimethalin
0.75-2.0
Piperophos + dimethame tryn 0.4 + 0.1
Piperophos + 2,4-D
0.3 + 0.2
Pretilachlor + antidote
0.3-0.4
Propanil
3.0-4.0
78 Weed control handbook
0.3
1.5-2.0
1.0 + 0.5
Comments and source of information
Apply 6-8 d after seeding (DAS)
(IRRI 1985).
Apply postemergence to control
broadleaf weeds and sedges,
including S. maritimus. Water level
must be lowered for good coverage.
Annual weeds must be small—2- to
7-leaf stages (IRRI 1984).
Apply at early postemergence of
weeds, about 4-6 DAS (IRRI 1981).
Apply 6 DAS to control annual grasses
and sedges. Soil should be saturated
at application and remain nonflooded
for 3 d after application (IRRI 1983).
Granular butachlor applied 3 DAS
gives better weed control, less stand
reduction, and higher yields than when
applied 6 DAS (IRRI 1986).
Apply 2-3 DAS to control annual
grasses (COPR 1976).
Apply 3-4 wk after seeding to control
annual broadleaf weeds and sedges.
Lower water level to expose weeds
before spraying and reflood within a
few days (COPR 1976).
Apply 6-7 DAS. Raise water level after
application (IRRI 1977).
Apply preemergence 4-6 DAS. Soil
must remain moist after application to
maintain herbicide activity (IRRI 1985).
Apply 3-6 DAS (IRRI 1978, 1982).
Apply up to 6 DAS (IRRI 1975, 1982).
Apply 4-6 DAS (IRRI 1977).
Apply 6-8 DAS (IRRI 1987).
Apply 3 DAS (IRRI 1987).
Apply postemergence to control grass
and broadleaf weeds at the 2- to 5-leaf
stages (about 10 DAS). Water level
should be lowered before application
and the field reflooded as soon as
possible (IRRI 1980).
Apply 6-8 DAS (IRRI 1986).
Apply about 6 DAS, when grasses have
1-2 leaves but before the 3-leaf stage of
grasses and sedges. Keep water low
enough to avoid submerging the rice
plants (IRRI 1972).
Apply 6-8 DAS (IRRI 1986).
Herbicides can be soil-incorporated
before sowing rice, applied preemer-
gence to water a few days after sow-
ing, or applied postemergence before
weeds reach the 3- to 4-leaf stage.
Table 6.2 and Figure 6.3 outline
various herbicides and their applica-
tion times for this rice culture.
Direct seeded on
dry soil
Dry seeded irrigated rice culture is
practiced in Africa, Australia, Europe,
and the USA. Nongerminated seeds
are broadcast or drill seeded in dry or
moist soil. Broadcast seeds are covered
by harrowing. More seeds are required
for broadcast than for drill seeding,
and stand establishment is poorer with
broadcast seeding than with drill
seeding.
Weed problems
After broadcast or drill seeding rice
into dry soil, the field is irrigated just
enough to provide the soil moisture
that allows the seeds to germinate.
Flooding the soil would prevent rice
seedling emergence. Thus, aerobic
conditions remain ideal for the germi-
nation of upland and aquatic weeds,
and weed problems are much worse in
dry seeded irrigated than in wet
seeded rice. Because the water level is
increased gradually, it is 2-6 wk before
a continuous flood at 5 cm depth can
be achieved. Many well-established
upland weeds will survive, making
weed competition more intense in
this rice culture than in the cultures
described earlier. The fact that rice and
weeds germinate together restricts the
number of herbicides that can be
used safely.
Land preparation
Land preparation should provide
weed-free conditions at planting and
favorable conditions for rice growth
and development. Land preparation
and leveling should be thorough
because large soil clods will reduce
germination of rice seedlings and
cause irregularity in herbicidal
efficacy. As clods melt down, the
inner, unexposed soil will allow weeds
to germinate.