Weeds and their Control

 

Common weeds in rice fields

Grasses:

  • Oryza rufipogon (varinellu),

  • Echinochloa crusgalli (kavada),

  • E. colona (kavada),

  • E. stagnina (kavada),

  • Isachne miliacea (chovverippullu, naringa).

Sedges:

  • Cyperus iria, (manjakora, chengoal),

  • C. difformis (thalekkattan),

  • Fimbristylis miliacea (mungai)

Broad leaved weeds:

  • Monochoria vaginalis (neelolppalam),

  • Ludwigia perennis (neergrampu),

  • Limnocharis flava (nagappola),

  • Ammania baccifera (nellicheera)

Ferns:

  • Salvinia molesta (African payal),

  • Marsilea quadrifolia (naalilakodian),

  • Azolla pinnata (azola)

Algae:

  • Chara spp. (chandi),

  • Spirogyra spp. (payal)

Weed management  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, 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 peddled conditions)

Spray any of the following herbicides:

(a) Butachlor @ 1.25 kg ai/ha  6-9 days after sowing;

(b) 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.

To control Echinochloa sp. spray cyhalofop butyl @ 0.08 kg ai/ha at 15-18 days after sowing.

In areas where wild rice has become a menace, the following agronomic practices can be followed.

a. 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.

b. Maintain the water level for 10-12 days to prevent germination of wild rice.

c. Drain the field and apply N and K fertilizer as per recommendation for rapid growth of the rice seedlings.

d. 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.

Where broad-leaved weeds and sedges are predominant, apply 2,4-D @ 1.0 kg ai/ha at 25 days after transplanting. Wherever the fields are level and water management could be effectively done, 2,4-D can be mixed with 10 kg urea/ha and broadcast on 20 DAS/DAT. This would save the spraying charges.

Trampling salvinia in situ in the wet lands a week before transplanting will control the weed and add to soil fertility.

Precaution while using herbicides

Keep the rice fields free from weeds up to 45 days either by hand weeding or by use of herbicides. In using herbicide follow the guidelines.
  • Apply herbicides at the recommended dose and time.
  • 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.
  • Spray without gaps and overlapping.
  • Use 300-400 litres of water per hectare for spraying the herbicide.
References Kerala Agricultural University.  2011.  Package of Practices Recommendations: Crops.14th edition. Kerala Agricultural University, Thrissur- 360 p.