s constitute a serious and continuing limitation to crop production in all agricultural systems, competing with the crop for growth factors like light, space, moisture, nutrients etc., with consequent reduction in yield to a great extent depending upon their intensity. Thus, weed management becomes very important component of modern day agriculture. So, in order to improve cost-benefit ratio, weeds must be kept under check with the use of any one or more weed control methods mentioned below.
When more than one method is employed for controlling weeds, it is termed as integrated method of weed management. This method is more effective because the left over weeds with one method can be controlled with other method. So, this method helps in reducing seed bank status in the field. With the adoption of this method, many problems such as shift in weed flora, development of resistance in weed plants etc., can be avoided. Also dependence on only one method, which may lead to many problems in the coming future, can be avoided. Integrated method of weed control is the need of the day and this method must be advocated in order to get long-term relief from these undesirable plants. Integration of chemical, mechanical, cultural or even biological method can be made for effective and; long time weed control. Integrated weed management approach is environmentally friendly as farmers are not entirely dependent on herbicides. So, need based use of herbicides should be done but integrated with other weed control methods which will reduce the quantity of herbicides usage causing economic benefits to the farmers.
Prevention, eradication and control are the fundamental principles of weed control. First basic step is to prevent the infestation of weed in a locality in order to avoid future problems. If one fails in preventing weeds, eradication step must be adopted. Eradication is limited on a very small scale and only when suitable methods of complete weed removal are available as eradication is cent percent control of weeds along with its root system and other propagative parts. In case one fails in prevention and eradication techniques then weed control method must be strictly followed in which the objective is to bring down the weed population (with any method) to a level that economical crop yield is possible. The aim of each weed control method is to achieve reasonable good control of weeds.
Care should be taken at the time of sowing of crops that weed seed free crop seed must be used. Before sowing, sieving should be done in order to sieve out weed seeds, broken and shriveled grains and diseased seeds. Check the seeds thoroughly and ensure that no weed seed is present. If it is not possible to separate out the weed seeds due to their similar size to that of crop seed, better reject that lot for seed purposes. The seeds of berseem are often infected with Kashni seeds. Dip the seeds of berseem in water just before sowing the seeds of Kashni being light in weight will float on the surface of water and seeds of berseem will settle at the bottom of the container. With the help of sieve remove the seeds of Kashni.
Farmyard manure (FYM) is a big source of weed seeds because weeds are usually fed along with fodder to the animals. Weed seeds in the viable form art excreted out of the digestive track along with excreta (cow dung). So avoid the use of raw FYM and always use well-decomposed FYM to get rid of weeds as well as termites.
When weed population is scanty and it is possible to uproot these plants, remove these before flowering and seed setting. This preventive technique will help in plummeting seed bank, which will be beneficial for the future years. Perennial weeds multiply in the permanent bunds and then enter in the field. Before sowing every crop, clean the field boundaries physically or spray non-residual herbicides like glyphosate. Similarly irrigation channels should be kept free from weeds in order to improve water use efficiency as well as reduce weed infestations. All the types of machinery must be cleaned while entering into the new field. All the type of cultivating equipment must be cleaned after ploughing weedy fields in order to remove weed seeds (sticking to soil) and vegetative parts of perennial weeds. Proper care must be taken while moving cultivating implements and harvesting compliance from one field to another field.
Removing the weeds physically or with tools/implements is called mechanical method. This is the oldest method adopted for the control of weeds since from the ancient times. Tillage is done mainly with two objectives.
(i) To uproot the weeds growing in the field.
(ii) To pulverize the soil in order to create ideal conditions for the seeds to germinate. There are different implements which can be used for this purpose such as cultivators, disc harrows, mould board plough, deep chiseller etc. Tillage helps in reducing soil seed bank to a great extent.
Hand pulling is the most common and very widely used method of weed control in field crops. A small implement like Khurpa (Khurpi), kasolla, spade, Baguri, wheel hoe etc., can be used for uprooting weed plants from different crops. In all crops the time of hoeing is very critical and it should neither be done too early nor too late but crop should be kept free from weeds at critical period of crop weed competition stage. This method is very safe but the only limitation is non-availability of labour, when required and is very expensive method. Hand hoeing can be done in all row-sown crops, solid drill and widely sown.
Intercultural method is the best method in which weeds could be conveniently controlled in wider row sown crops such as maize, cotton, sugarcane, pigeon pea etc. Interculture can be, done with bullocks or with tractor by adjusting the distance between the tines so that crop rows are not hampered. It is very quick method as compared to hand hoeing and can be practiced over a large area. Moreover, this method is very effective for controlling later flushes of weeds. The limitations in this method are that weeds growing in the vicinity of crop plants are not controlled and some times the crops, which have lateral spread of roots, suffer due to root injury. Even the spread of plant diseases may also take place as in potato.
Weeds can also be effectively controlled with the adoption of different cultural operations. Crop rotation is the best and non-monetary technique for weed management because weeds are associated with certain crops due to their identical ecological requirements. This method, no doubt, is very helpful in reducing or even eliminating many specific weeds, but it cannot be practiced on a large scale. The practical utility of this method is limited to small scale. For instance problem of Canary grass in rice-wheat system can be overcome very effectively by replacing wheat with berseem. However, area under berseem is limited and it cannot be increased beyond the demand of fodder in a particular locality. Similar is the case with other rotations.
After studying biology of a troublesome weed, the sowing of the crop can be manipulated in such a way that ecological conditions for germination of weed seeds are not met due to escape mechanism.
The increased yield of crops particularly with tillering habits is not directly correlated with increase in seed rates but these yield improvements are due to reduced crop weed competition imposed by higher crop plants pressure per unit area. Higher density of crops helps in reducing uptake of nutrients and moisture by weeds and also results in providing less space and less interception of light by weed plants. So, overall growth and development of weed plants will be poor, when crop density is on the higher side.
Planting pattern is uniform distribution of plants of crop per unit area even with same seed rate by providing better crop architect. Placement of fertilizer is very beneficial in providing lead to the crop due to its quick and more available and more availability to crop plants as compared to weed plants. Varieties with initial quick growth and more leaf area must be preferred in order to reduce crop weed competitions.
Primary role of tillage is to up root the germinating and germinated weed seedlings. In conservative tillage system, weed seeds present in the top soil zone are forced to germinate with pre-sowing irrigation and can be killed with any contact herbicide and crops can be sown without any tillage operations. With the adoption of this method weed population in crop is expected to come down.
Sometimes sufficient time is provided to weed seeds to germinate before sowing the-crop. Either double pre sowing irrigation is given or field is kept for 8-10 days (during winters only) after land preparation to encourage weed to germinate. These germinated weeds can be ploughed up at the time of land preparation or can be killed with the use of any contact type herbicide irrigation management has direct or indirect effect on weed intensity. In drip irrigation the weed intensity is generally lower than in furrow irrigation method. Similarly, in alternate furrow irrigation, low weed intensity is observed in dry furrows than in irrigated furrows.
Soil solarization is a novel technique of controlling soil born pests including weeds. It involves covering the wet soil with thin transparent polythene films during the summer months.
No doubt, agronomic manipulations help in reducing weed population but-under certain situations, we cannot entirely depend on these practices. One should not depend fully or cultural practice and this method should be integrated with chemical or mechanical method of weed control if need be. Cultural practices are non-monetary methods and help a lot in bringing down infestation level of weeds.
Control of weeds with the use of inorganic chemicals called herbicides that' are toxic to certain categories of plants is called as chemical weed control method. As compared to mechanical method, chemical weed control method has many advantages.
In order to obtain higher yields, weeds must be controlled before the critical period of crop weed competition that is generally between 2-6 weeks after sowing of most of the crops. This period varies with crop and season in which it is raised. Pre-emergence as well as post-emergence application of herbicides is done before critical period of crop-weed competition on starts. So, chemical method of weed control provides good environment for the crop for its initial growth and development.
Few weeds particularly during initial stages have similar morphological appearance as of crop, for example, Canary grass as well as Wild Oat with wheat or barley at the time of hoeing. Identification of these weeds is a big problem and these plants are left in the field considering them as crop plants. So, with the use of selective herbicides in wheat, these morphologically similar weeds can be controlled very effectively. Moreover, intra row weeds are not controlled with hand hoeing/interculture.
But on the other hand both inter and intra-row weeds can be effectively controlled with the use of herbicide due to their selectivity phenomenon. So, the uncontrolled infix row weeds in mechanical method compete with crop for growth factors and produce seeds also. Sometimes due to continuous rains or due to non-availability of timely labour mechanical method cannot be implemented. With delayed hoeing not only labour expenses are increased but also overall net returns are reduced due to severe competition with weeds. However, there is less risk of rainfall or other climatic factors on the adoption of chemical method.
The fields, which are very clayey in texture, do not come in proper moisture condition for hand hoeing and hoeing operations are either delayed or omitted due to continuous wet field conditions. Moreover, hoeing of such fields results in establishment of uprooted weeds. On the other hand with the use of herbicide weeds can be effectively controlled in these types of situations. Herbicides with ideal residual periods provide good control of such category of weeds.
The weed plants are killed in situ (where they are) with the use of herbicides. However, with mechanical methods, uprooted weeds are dragged to new site where they re-establish of soil is clayey in texture and optimum moisture is present. This problem can be faced during winter months or in Rabi crop.
Pruning of the roots of crops takes place with hoeing of interculture technique, which may prove harmful for overall crop development. However, such type of losses does not occur in chemical weed control method. As we know that frequency of tillage operations depends upon weed density along with type of weed flora. Crops can be sown without any tillage operation with the use of non-residual also called zero-till herbicide. So uses of herbicides are substitute of tillage operations, which cut down the cost of cultivation to a great extent. The use of glyphosate or paraquat can be successfully made depending upon weed flora to minimize tillage operations. Chemical weed control methods though played key role in green revolution but simultaneously it created new problems is today's agriculture.
In general, farmers do not adopt proper application technology for spraying herbicides. Mostly farmers do not stick to the recommended dose and time of application. Due to these drawbacks desirable control of weeds is not attained. Continuous use of one group of herbicide may lead to either shift in weed flora or development of resistance in weeds. So, in, order to avoid such problems, rotational use of different herbicide groups should be made so that all type of weed may be controlled. Drift or run-off of herbicide can cause damage to the neighbouring crops. When high velocity winds are blowing at the time of spraying some sensitive crops growing in adjoining fields may be damaged. Under high temperature conditions, volatilisation of applied herbicide may harm sensitive crops even to a long distance. Similarly with heavy rain fall, run off losses of applied herbicides can damage sensitive crops.
Some times crop does not germinate either due to poor seed quality or due to toxic effect of herbicide. Under such situations farmer is left with no option.
Some mischievous farmers use these chemicals as weapon for taking revenge of their enemies (neighbour). During off times they spray or broadcast non-selective herbicides on their fields (enemies) and slowly crop is totally damaged. Few herbicides due to their high cost are out of the reach of an average farmer. There is no doubt that net benefit is increased to a higher level with the use of such herbicides. However, only disadvantage is that their initial cost high.
The residues of herbicides are harmful for human and animal health. Apart from this the long soil persisting herbicides prove hazardous for succeeding crops. So, ideal pesticides must be eco friendly wit desirable residual effects. Continuous use of herbicides over a longer period can pollute underground water. In the final analysis it may be said that there is dire need to use all above-mentioned tools in a wise and timetabled procedure. Similarly it is also necessary to discover any sound and indigenous resources based biological control of weeds in wheat crop, which will be a good friend to us to combat with the obnoxious weeds to ensure more quantity and better quality of field crop production.