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Common weeds in rice fields of Kerala are:
Grasses:
- Oryza rufipogon (varinellu)
-
Echinochloa crusgalli (kavada)
-
E. colona (kavada)
- E. stagnina (kavada)
-
Saccolepis interrupta (polla)
-
Isachne miliacea (chovverippullu, naringa).
Sedges:
- Cyperus iria, (manjakora, chengoal)
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C. difformis (thalekkattan)
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Fimbristylis miliacea (mungai)
Broad leaved weeds:
- Monochoria vaginalis (neelolppalam)
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Ludwigia perennis (neergrampu)
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Limnocharis flava (nagappola)
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Ammania baccifera (nellicheera)
Algae:
- Chava spp. (chandi), Spirogyra spp. (payal)
Ferns:
- Salvinia molesta (African payal)
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Marsilea quadrifolia (naalilakodian)
-
Azolla pinnata (azola)
Control
Keep the rice fields free from weeds up to 45 days either by hand weeding or by
use of herbicides. The recommendation for the use of herbicides in different system
of rice culture are given below.
A. Dry seeded rice [upland and lowland (semi-dry) rice]
Spray any of the following pre-emergent herbicides:
- butachlor @ 1.25 kg ai/ha
- oxyfluorfen @ 0.15 kg ai/ha
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pendimethalin @ 1.50 kg ai/ha
-
pretilachlor @ 0.75 kg ai/ha on the same day of seeding or within six days of seeding.
B. Wet seeded rice (direct seeding with sprouted seeds
under puddled conditions)
Spray any of the following herbicides:
- Butachlor @ 1.25 kg ai/ha 6-9 days after sowing;
- Pretilachlor + safener (sofit) @ 0.45 kg ai/ha 3-5
days after sowing
Give a follow up application of 2,4-D @ 0.8 kg ai/ha at 20 days after sowing.
- Pretilachlor @0.45kgai/ha at 3-4 DAS and one light hand weeding at 28 DAS for wet
sown rice in Kole land.
Control of Echinochloa sp.- spray cyhalofop butyl @ 0.08
kg ai/ha at 15-18 days after sowing.
In certain areas like Kuttanad, wild rice has become a menace in recent years. If
effective water control is possible, the following agronomic practices can successfully
control the infestation of wild rice.
- Coat dry seeds with 20% calcium peroxide using 4%
PVA solution as an adhesive and then broadcast in the field with 10-15 cm column
of standing water.
- Maintain the water level
for 10-12 days to prevent germination of wild rice.
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Drain the field and apply N and K fertilizer as per recommendation for rapid growth
of the rice seedlings.
- Where yeranda
(common teal) is a problem, bird scaring should be arranged till the water is drained.
C. Transplanted rice
Apply any of the following herbicides at 0-6 days after transplanting.
- pendimethalin @ 1.5 kg ai/ha
- butachlor @1.25 kg ai/ha
Pendimethalin @ 1.5 kg ai/ha, butachlor @1.25 kg ai/ha. For controlling broad leaved
weeds and sedges 2, 4-D sodium salt may be applied @ 1 kg ai/ha on 25 DAT. Pre emergence
application of 2, 4-D sodium @ 0.8 kg ai/ha on 5 DAT can control all the three groups
of weeds viz. grasses, sedges and broad leaved weeds.
Wherever fields are levelled and water management could be effectively done 2, 4-D
can be mixed with 10kg urea/ha and broadcast on 20 DAS/DAT. This would save the
spraying charges.
Apply 2,4-D Na salt as pre-emergence broad-spectrum herbicide @ 0.8 kg ai /ha at
5 days after transplanting. Spray on moist soil surface with a fan nozzle to give
blanket coverage. Use 300-400 litres of spray fluid.
Almix 20WP(Chlorimuron ethyl 10% +Metsulfuron methyl 10%@ 4g ai ha-1+ 0.2% surfactant
at 20-25 DAS/DAT is equally effective as 2,4-D for controlling sedges and broad
leaved weeds in rice fields. This herbicide is effective for controlling Marsilia
quadrifolia also. Almix can be given as follow-up application to cyhalofop butyl
used for the control of grass weeds with a minimum of one day gap between the applications.
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Management of Salvinia Molesta (African Payal)
Trampling Salvinia insitu in the wet lands a week before transplanting will control
the weed and add to soil fertility. Herbicides should be applied in areas where
protected drinking water supply is available.
Release of Cyrtobagous salviniae weevils is found effective for the control
of salvinia. Even one pair of weevil is sufficient for establishment in a locality.
But for practical consideration 50 to 100 weevils are recommended for release in
a particular area. When collection of weevil is not possible, about one kg of infested
salvinia can be used as the inoculum. Release may preferably be made whenever tender
salvinia growth is available. If the plants are very old, they may be removed mechanically
to promote re-growth and then weevils are to be released. Almost 100 per cent control
of the weed will be obtained in a span of 12-18 months. The rate of natural dispersal
of the weevil is rather slow and hence it is desirable that the infested weed mats
are redistributed at periodic intervals. In canals used for navigation, the rate
of spread of the weevil is found to be quite adequate.
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Precaution while using herbicides
- Apply herbicides at the recommended dose and time.
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Drain the field before herbicide application.
- Re-flood after 48 hours to prevent further weed germination
when post emergent herbicides are used. For pre-emergent herbicides, wait for a
week before re-flooding the field.
- Use
herbicide nozzle (flood jet / flood fan) for herbicide application.
- Move at uniform speed when applying herbicides.
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Spray without gaps and overlapping.
- Use 300-400 litres of water per hectare for spraying
the herbicide.
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