WHAT IS INTEGRATED WEED MANAGEMENT (IWM)
Integrated weed management is defined as the combined use of all the methods of weed control i.e. cultural, physical, chemical and biological methods in such a balanced way so that there is no harmful effect of weed control practices on nature and side by side weeds are controlled and managed effectively. It aims at bringing down the weeds intensity to such low levels so that they do not pose any significant danger to crops and humans. It uses the creative application of agronomic, biological and chemical methods to control weeds. IWM is the need of the situation as today the world is facing the problem of environment pollution due to the use of harmful and strong chemicals in curing weeds which pollute the land, air & water very badly.So pollution free environment is essential for sustaining life on earth, weeds .which can be brought by using IWM in weeds.The certain advantages of integrated weed management are listed below:
a. The shift in crop weed competition in favour of crops.
b. Prevents the weeds from changing into perennial nature.
c. Prevents the resistance to herbicides in weeds.
d. Minimum pollution of the environment.
e. Contribute towards the economic crop production.
f. Minimisation of the danger of herbicide residue in soil or in plants.
CHEMICAL METHODS OF WEED CONTROL
Chemical methods offer a great potential for weed control in crops.There are certain chemicals which function on the basis of selectivity by killing only the weed plants and not affecting the crop or valuable plants.Such chemicals are known as herbicides. Chemicals or herbicides were first invented in 1933 as Dinoseb, MCPA & 2,4-D in 1945. The usage of herbicides consumption is 43% which is highest among insecticides (34%), fungicides(21%) & 5% with other agrochemicals.herbicide market in the overall world is increased by many folds in past 20 years or so. The various groups of chemicals used are:
a. Chlorophenoxy compounds
b. Substituted aliphatic acids
c. Benzoic acids
j. Substituted ureas
k. Sulphonyl ureas
The main advantages of chemical weed control are as follows:
1. Most effective as compared to other methods of weed control.
2. Very suitable for closely spaced crops.
3. Provides early season weed control.
4. Suitable for adverse soil conditions.
5. Controls many perennial weeds very effectively.
The main drawbacks of chemical methods of weed control are that they must be applied at the proper time & with proper care; also they have harmful residue problem which has an effect on succeeding crop & also they require some technical knowledge to use.
MECHANICAL OR PHYSICAL METHODS OF WEED CONTROL
The mechanical or physical methods of weed control are being used since man used to grow crops.It includes various methods like hand hoeing, hand pulling, tillage, digging, sickling, burning, flooding & mulching etc.But each of these methods is labour & time consuming as well as not of complete or full weed control.These methods are listed in detail below:
- Hand hoeing: Hand hoe is the simplest tool to control annual & biennial weeds which have shallow root system under this system, but it can not be able in controlling deep rooted & perennial weeds.
- Hand pulling: It is pulling out of weeds by hand.It is very economical in those areas where weeds are scattered & very effective against annual & biennial weeds as they do not regenerate from pieces of roots left in the ground.
- Tillage: Weeds can be controlled by various tillage operation such as ploughing, harrowing, planking, levelling etc. Many perennial weeds ca also be controlled by deep ploughing continuously for a period of 3 or 5 years.
- Digging: Under digging the underground propagating parts of perennial weeds are removed from the deep layers of soil.It is followed by hand pulling the weeds.But it is a labour intensive method which is its main drawback.
- Sickling: Sickling is mostly used in case of sloppy lands to remove top weed growth & to prevent weed seed production.
- Burning: In this method, the weeds are burnt with fire along with crop residues in certain crops like sugarcane, potato, maize, cotton etc.
- Flooding: Here the weeds are managed by flooding the field with 20 -30cm standing water for 5 to 10 weeks. It is very much useful in some perennial weeds like Cyperus sp., Cynodon dactylon & Convolvulus arvensis.
- Mulching: It has a smothering effect on weeds by restricting the photosynthesis. Mulching is effective against Sorghum halepense, Cynodon dactylon etc.Mulching can be done by straw, hay, paper, polythene films etc. in cash crops.
AGRONOMIC OR CULTURAL METHODS OF WEED CONTROL
These practices for weed control are mostly non-monetary & relatively of less expenditure.these methods can be used to reduce the intensity of weeds to improve crop yield.The main objective of cultural practices is to provide a short-term relief to crop during initial growth periods of crop production.The various practices involved under the cultural method of weed control are listed below:-
- Planting or Sowing time :As it is a proved fact that weed seeds are thermosensitive in nature, so by adjusting the planting or sowing time of crop plants we can exert a smothering effect on the weeds so that the crop plants have the early advantage over the weeds & therefore, offers less competition for the crop plants.For eg.)if wheat is early sown then Phalaris minor has less advantage over the wheat crop.
- Use of clean seed: To ensure that the crops must be free of primary weed infestation the crop seed must be free from weed seeds.Phalaris minor was imported along with Mexican wheat seed & then spread to many parts of Indian subcontinent through movement of wheat seeds from place to place.
- Stale seedbed preparation: The main objective of this technique is to induce germination of weed seed with irrigations before sowing the crop so that 2-3 flushes of germinated weeds are destroyed.This method is ideal for the crops in which germination of crop & weed seed is synchronised.
- The method of sowing: Closed spacing of crops always gives a chance to the crop plants ahead of weeds.Also, bidirectional sowing of crops helps in reducing weed growth as the distribution of plants over the space becomes adequate & healthy crop canopy structure can be generated which can cover the weeds effectively.
- Proper seed rate : higher seed rate enjoys an advantage over the weeds as thick crop stand reduces space for weeds to grow & establish themselves.
- Crop rotation :Crop rotation is also helpful as monoculture or growing of same cropping system allows the pure stand of some permanent weeds which are very difficult to control .for eg.) some permanent weeds of rice -wheat cropping system such as Phalaris minor & Echinocolona sp. can be controlled by replacing wheat with berseem, raya or winter maize.Wild oat can be completely managed from wheat by replacing it with berseem for 3-4 years.
- Intercropping: Weeds can also be manged effectively by intercropping of wide row-spaced crops with closed row-spaced crops & of tall growing crops with short growing crops.Efficient intercrops are cowpea, green gram, black gram, soybean etc.
- Water management: weeds can also be managed properly by managing irrigation.The role of land submergence in lowland rice has been well noticed all over the world.Under normal irrigations to wheat crop wild oat make luxuriant growth & affect the wheat crop, but in limited irrigation, the wheat plants overtake the wild oat & suppress their growth & development.
BIOLOGICAL METHODS OF WEED CONTROL
These methods involve the utilisation of natural living organisms i.e. bioagents such as insects, pathogens & competitive plants to limit the weed infestation .the objective of biological control are not the complete eradication of weed population but bring their population below the economic injury level.the merits of biocontrol agents are their relative cheapness, environment comparatively long lasting effects & least environment & the non-target organisms.Some outstanding examples of biological control of weeds are:
a.Control of Eichhornia crassipes (water hyacinth) using Necochetina eichhorniae (hyacinth weevil);
b.Salvinia molesta (water fern) is controlled by Crystobagus spp. ;
c.Lantana camara in India has been effectively controlled by a moth Crocidosema lantana;
d.Zygograma bicolorata beetle feeds on Parthenium plants during the rainy season.
Weeds can also be controlled by this method with the help of bioherbicides such as Collego, Devine, Biopolaris, Tripose etc.