The major weeds found in SRI system of paddy cultivation are Marsilia sp. , Echinocloa sp., Monochoris vagilalis, Cyprus iria and Cyprus deformis. The effective integrated weed management adopted are
1. Passing cono weeder at 10, 20, 30 and 40 days after transplanting OR
2. Application of pre-emergence herbicide like butachlor 50% EC @ 1500 g ai/ha 3 DAT + two cono weeding at 20 and 30 DAT.

1. The allelopathic potential of weeds through the release of toxic substances into the environment either by root exudation or from decaying plant material has been demonstrated in about 90 species (Putnam 1986). 2. Rice germination, growth and yield were significantly reduced by leachates from C. rotundus and this inhibition might be due to the presence of allelopathins. Among the whole plant extracts of Lantana camara, Cyperus rotundus, Ageratum conizoides, Echinochloa crusgalli, Commelina benghalensis and Xanthium strumanium, except for those of E. crusgalli and C.

1. Allelopathic compounds are released directly or indirectly into the rhizosphere by leaching, residue incorporation and decomposition, volatilization, root exudates etc. Research indicates that bio chemical interaction takes place when allelochemicals produced by one plant escape into environment and influence the growth and development of another plant.

1. Plants are known to release chemicals into the environment by several means which, depending upon edaphic and climatic factors, may influence the growth of neighbouring species.

2. This phenomenon could be exploited for the development of eco-friendly (nonchemical) weed management through the use of
a. allelopathic cover crops,
b. allelochemicals as natural herbicides,
c. allelopathic crops cultivars.

1. Natural or biological weed control agents are those of biological origin, which suppress or kill the weeds without significantly affecting the desirable plants. They include insects, animals, fish (like Chinese carp), snails, birds (like duck), microbes (fungi, bacteria, viruses, nematodes, etc.), their toxic products, and plants (parasite plants, competing plants) or their products.

1. Crops that are normally susceptible to herbicides can be made into herbicide tolerant crops by employing biotechnological tools. Resistance genes for several herbicides have been incorporated into the genome of corn, cotton, canola and soybean.

1. Continued use of a single herbicide will result in a shift of weed species to those that are tolerant or resistant to the herbicide or to individuals within the same species that become resistant to the herbicides. In Korea, annual weeds such as Echinochloa crusgalli and Monochoria vaginalis, and perennials such as Sagittaria trifolia, Sagittaria pygmaea, Eleocharis kuroguwai, Cyperus serotinus and Potamogeton distinctus, have been the most important weed species in paddy fields.

 Herbicide applicators are for distributing an exact quantity of herbicide uniformly over an area.

i) Pressurized applicators – Hydraulic applicators (Knapsack sprayer)

ii) Non-pressurized applicators – Granular applicator, Water gun, Direct contact applicator, Controlled–droplet applicators.

1. Pre-plant applications are sprayed on the foliage of existing vegetation prior to planting or they are made to the soil and may be incorporated in areas where rainfall is unpredictable or if the herbicide is volatile or is subject to rapid photo-decomposition.

2. Post plant applications may be made  to the soil surface following planting and prior to emergence of either crop or weeds (pre-emergence) or  to the weed and crop seedling whether in contact with the plant foliage or into the water (post-emergence). 

 1. Spray in morning or evening hours when gentle wind is there and away from sensitive crops

2.  Use only minimum pressure required for nozzles to operate

3.  Use large nozzle tips for larger spray volumes, larger size droplets

4.  Hold the sprayer nozzles close to the target

5. Leaving a 10 metre wide strip of rice crop unsprayed where neighbouring crops are sensitive.

6.  Non chemical methods of weed control  can be followed in the unsprayed strip

 1. Herbicide drift occurs when the smaller drops in the spray are carried away from the target area by wind or when vapour from a volatile herbicide is carried away during or after spraying. 

e.g: 2,4-D (growth regulator herbicide) causes greatest drift damage to sensitive crops like tomato, lettuce, cotton, fruit trees.

1. The soil acts as an important buffer governing the persistence and fate of most herbicides in the environment. Herbicides have lower residue concern over pesticides.

2. Herbicides applied at planting or during early stages of crop growth, giving more time for degradation of the chemical in the plant and environment and making residues at harvest to be negligible.

 3.  Tropical climate enable faster degradation of chemicals. Majority of herbicides when applied at recommended doses have not been detected in food chain or in soil of concern. 

 1. Degree of weed species and weed growth

 2. Recommendations for weed control

 3.  Available control measures

4.  Correct timing of herbicide application

 5. Experience in spraying

 6. Probable cost-benefit of applying the herbicide  safety

 1. Commercial solid formulations (WP, WSP, Granules) – concentration is expressed as percentage of the weight of the active ingredient by the weight of commercial solid herbicide (weight/weight).

2. Commercial liquid formulations - concentration is expressed as the weight of the active ingredient by the volume of the commercial emulsifiable concentrate herbicide (weight/ volume). Different herbicide formulations are  given below,

Herbicides should not be applied like, insecticides and fungicides. Specific nozzles are used for herbicide spraying.

Flat fan nozzles: They produce a tapered edge, fan pattern for broadcast spraying and when foliar penetration and coverage are not required. The operating pressure should be low so that medium to coarse droplets.

1. Anilides: Eg. Butachlor, Pretilachlor, Propanil

2. Bypyridyliuns: Eg. Paraquat

3. Dinitro anilines:  Eg. Butralin, Pendimethalin.

4. Organophosphorus compounds: Eg. Glyphosate.

5. Phenoxyacetic acids Eg. 2,4,D, Fenoprop, MCPA, 2.4.5.T

6. Thiocarbamates Eg. Molivate, Thiobencarb

7. Triazimes Eg.  Simetryn, Dimethametryn

8. Sulfonylureas Eg. Bensulfuron

9. Polyclic alkalnoic acids Eg. Fenoxaprop

10. Miscellaneous herbicides Eg. Beutayon, chlomethoxynil,cinmethylin, Oxadiaryon, Piperphos,Quinclorac.

1. Among all methods, chemical control is effective and herbicides being cheap, reliable, have facilitated a revolution in crop agronomy. Currently, herbicides share about two-third by volume of the pesticides used in agricultural production. 

1. The  use of hand operated or power operated weeders is feasible only where rice is planted in straight rows. 

 2. Hand weeders such as rotary and cono weeders are not effective if land is too dry or in standing water. 

3. The pushed weeders are in common use. The weeder should be run in both the directions, at right angles to each other.