Rice

Weed Management

Introduction Control Chemical Weed Control


Introduction

Weed

  • a plant growing out of place
  • an unwanted plant, non-useful, persistent and prolific
  • a plant effectively competes with crop plants for space, nutrients, sunlight and water.
  • hardy plant

Weed characteristics

  • growth rate in very high
  • deep root system
  • more uptake of moisture and nutrients
  • tolerant to severe conditions
  • more dormancy period
  • Large number of seeds/plant
  • Small size seed
  • High photosynthetic efficiency

    • Losses Through Weeds

     
    • Interferes with agricultural operations
    • Loss of crop yield and quality of produce
    • Higher crop losses over any other agricultural pests

    Yield reduction due to weeds was estimated to be around

    15-20% in transplanted rice 30-35% in direct seeded rice 50% in upland rice 5As per AICRP and DRR
    34% in transplanted rice 45% in direct seeded rice 67% in dry paddy 5As per I.R.R.I Philippines

    • Total loss of rice yield due to weeds (INDIA) = 15 mt/year
    • Total loss of rice yield due to weeds (world) = 9.5% per year
    • Cause more yield loss in Kharif over Rabi season.
    • Acts as alternate hosts

    Ex: Grassy weed (Leersia oryzoides) - alternate host or bacterial leaf blight Panicum SPP - alternate host for rice stem borer.

    • Cause soil nutrient loss to an extent of 14 kg N, 2.3 kg P2O5 and 25.3 kg K2O when weeding is not done.

    Common Weeds In Rice Crop

  • Common weeds in rice fields grouped into three categories,
  • Grasses,
  • Sedges, and
  • Broad leaved weeds

Grasses

  • Grasses are the monocots with two ranked leaves, that are usually long, narrow and upright with parallel venation's.
  • Resemble rice crop the stems are more or less round in shape, possess nodes, internodes are generally hollow with scattered vascular bundles.
  • Leaves have ligule and auricle at the junction of lamina and leaf sheath. Some of the grassy weeds are as follows,

Echinochloa colonum

Echinochloa crussgalli

Setaria glauca

Dactyloctenium aegyptiacum

Digitaria longifolia

Cynodon dactylon
  • Saccharum munja
  • Eleusine indica
  • Eragrostis interupta
  • Paspalum scrobiculatum
  • Leersia hexandra
  • Eragrostis aspera

Sedges

  • Sedges are very similar to grasses but have three ranked leaves.
  • The stems are usually triangular and they won't possess nodes and internodes.
  • Several species have modified rhizomes which are used for food storage and propagation. Some of the sedges are given below,

Cyperus rotundus

Cyperus iria

Cyperus difformis

Fimbristylis milliaceae
  • Scirpus erectus
  • Cyperus haspan

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Control Measures

  • Thorough puddling, proper levelling and irrigation management control germination and growth of weeds.
  • Working with rotary weeder (push hoe) in line planting rice at 20,30 and 40 days of crop growth.
  • Manual weeding (common practice) in random planting rice at 20 and 30 days after transplanting.
  • Manual weeding is costly and also due to non-availability of labor now-a-days,other methods of weed control gaining importance. Biological Control Of Weeds
  • Certain insects and microbes feed on weeds and contributing to the weed control.

  • Some of the examples where the weeds are controlled through biological method are furnished below.

Weed Species
Natural Enemies
Cyperus rotundus Athesapenta cyperi (Rhizome and stem boring weevil), Bactra minima (Tertric stem borer), Bactra venesoma.
Salvinia molesta (Water fern) Grasshoppers Paulinia acuminata
Hydrilla, Chara (Water fern) White amur, Tilapia (Fishes).

In rice crop both pre-emergence and Post-emergence herbicides are being used

  • Pre-emergence herbicides is one i.e. applied prior to the emergence of crop of weed
  • Post-emergence herbicide is one which is applied after the emergence of crop or weed.

The following herbicides are used for the control of different weeds in the rice ecosystem

  • Butachlor (Machete, wiper, Delchlor, Hitachlor) is available as 5 G and 50 EC. This is used as pre-emergence herbicide @ 1 to 2 kg a.i./ha within 5 days after transplanting for control of grasses and sedges.
  • Anilophos (Arozin, Aniloguard) is available as 3 G and 30 EC. This is used @ 0.3 to 0.4 kg a.i./ha within 6-10 days after transplanting for control of grasses.
  • Benthiocarb (saturn) is available as 10 G and 50 EC and used @ 1.5 kg a.i./ha within 4-6 days after transplanting for control grasses.
  • 2,4-D ethyl ester (knock-weed, Agrodar, smash) is available in the form of 4 G and 36 EC. Only granules are recommended for control of broad leaved and sedge weeds with application of 0.8 kg a.i./ha within 4-6 days after transplanting.
  • 2,4-D Sodium salt (Fernoxone, 2,4-D Knock-weed) is available as 80 WP and it is recommended @ 5.6 kg/ha in 1125 litres of water. The spray fluid should be sprayed on the soil one month before transplanting and this weedicideis effective in controlling weeds that appear prior to planting.
  • Propanil (Stam F-34) is available as 34 EC anf can be used during post planting stage i.e. 15-25 days after planting for the control of grasses and also, against certain broad leaved weeds to some extent @ 11.52 litres in 500 liters of water. Before spraying this weedicide, water should be drained. This weedicide can also be used in the nursery and also in dry paddy.
  • The combination of 2,4-D ethyl ester at 0.5 kg a.i./ha with Butachlor at 1 kg a.i./ha or Benthiocarp at 1 kg a.i./ha or Anilophos at 0.3 kg a.i./ha within 4-6 days after transplanting is useful for controlling all types of weeds. i.e., grasses, sedges and broad leaved weeds.

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Weedicides used in Rice

Group
Other name
Formulation
Application season
1.Benthiocarb S-(4-chlorophenyl) methyl dithyl - carbamotriate Saturn, Saturno E.C,10% G. Pre-emergence and early post-emergence herbicide for control of grasses, broad leaf weeds that infest rice fields, both wet seeded and dry seeded.
2. Butachlor 2 chloro - 2,6 - diethyl - N - (butoxy - methyl) acetanilide CP53619 5% G, E.C For pre-emergence control of annual grass and certain broad leafed weeds in both transplanted rice grown in certain Asian and South American area.
3. Oxadiazone (2 - tertiary - butyl - 4 - (2,4 - dichloro - 5 isopropoxyphenyl) 2 1,3,4 - Oxadiazolin - 5 -one ) RP17623 E.C and Granules. Pre-emergence and early post-emergence control of annual grasses and broad leaf weeds.
4. Fluchloralin (N - (2 - chloro ethyl - a, a, a, - trifluro, - 2,6 dinitro  - N propyl - P - toluidine. )   E.C Pre-plant and pre-emergence incorporated, for the control of annual grasses and certain broad leaf weeds
5. 2,4 - D (Lithium 2,4 - dichlorophenoxy acetate)   5% G Used as a post-emergence application for the control of broad leaf weeds
6. Lolop Granules (Pytolidynyl 2,4 - dichlorophenyl carbomate )   5% G Herbicide for paddy weeds
7. Nitofen (2,4 - dichloro phenyl P-nitrophenyl ether). NIP E.C 25%, W.P 50% and 7.7% G Pre or post emergence Control of no. of weeds in rice. Incorporation not recommended
8. MCPA (4 - chloro - o - methyl oxy acetic acid ) Agroxone, Rhonox With various free hormone type herbicide A translocated herbicide used as post-emergence for the control of annual and perennial broad leaf weeds
9. Propanil (3,4 - Dichloro phenyl propionanilide ) Bay 30130, Chemrice E.C 2%, 25% For post-emergence application to kill barnyard grass and various water weeds in rice
10 Bentazon (3 - isopropyl - 1, H - 2, 1, 3 - benzothiadiazin (4) - 3H - one   2, 2 dioxide )   Soluble concentration as the sodium salt of bentozone Selective post-emergence control of broad leaf weeds
11.Pendimethaline (N - (1 - ethyl propyl) - 3,4 dimethyl - 1,2,6 dinitro benzenamine ) Prowl, Stomp E.C WP, G Selective pre-plant incorporated - pre-emergence herbicide for the control of annual grass weeds and certain broad leaf weeds
12.Paraquat. (1,1-Dimethyl-4,4- bipyridinium ion Present as the dichloride salt.) Dextrone, Gramoxone Granular For desication of seed crops, for non crop and industrial weed control in bearing and non-bearing fruit orchards, shade trees, and ornamentals. For killing potato vines and aquatic weed control.
13.Dalapon (2-2 dichloro propionic acid ) Basfapon ,Unipon   Effective against quack grass , bermuda grass, johnson grasss and other perennial grasses Often it is used as a pre plant treatment to control established perennial grasses in crop land. It is translocated to the roots of most SPP and acts as a growth regulator.
14.Glyphosate (N-(phosphonomethyl ) glycine )     Shows much promise for the control of johnson grass applied just after harvest of such crops as grain sorghum and cotton. Pre emergence for the control of both perennial and annual weeds as a foliar application.
15.Molinate (S-Ethyl hexa hydro-1,H-azepine-1,carbo thionate )   Emulsifiable liquid (8 pounds/gallons) ,Grannules 5% Particularly effective for control of water grass in rice.
16. Amitrole (3, Amino-1,2,4-triazole )     Pre-emergence and post emergence

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