Farmers had been busy in controlling weeds by different local approaches. It would be a faint dream to expect high crop yield potential without taking weed management in account. Crops can never achieve the potential claimed by the breeders because of environmental hazards and management constraints and I reckon the weeds as number one threat in this regard. Under such circumstances, farmers own varieties or land races are better yielder
PAKISTAN HAS diverse climatic conditions providing the opportunity to grow a wide range of field crops. The problem of weeds diversity is increasing due to the changing patterns of climate and farming practices. Weeds inflict 20-30 per cent losses in different crops on the average. On national level total monitory losses due to weeds well exceed beyond 120 billion, whereas wheat alone accounts for more than 30 billion. Following pictures give a clear idea of magnitude of loss due to weeds and the significance of their control.
• Parthenium hysterophorus (Sarkari Booti)
• Cnicus benedictus (Kandali)
• Avena Fatua (Jangli Jai)
• Rumex dentatus (Jangli Palak)
Weeds are the plants with specific features helping them to infest and invade in the crops and to succeed under a wide range of environmental and climatic conditions. Weeds act differently in different habitats. Weeds also provide shelter to the insects and diseases causing pests, resultantly lowering the quality of produced and sometimes cause complete failure of crop. Farmers had been busy in controlling weeds by different local approaches. It would be a faint dream to expect high crop yield potential without taking weed management in account. Crops can never achieve the potential claimed by the breeders because of environmental hazards and management constraints and I reckon the weeds as number one threat in this regard. Under such circumstances, farmers own varieties or land races are better yielder and competitors as compared to the modern improved cultivars.
Conventional Cultural Practices:
In Pakistan main focus was on mechanical methods of weed management. Indigenous cultural practices are more important in weed management. Most importantly tillage has been used as significant tool to control range of weeds. Tillage provides different types of natural and manipulated habitats to the weeds. Previously the farmers of Pakistan used old tillage implements to control weeds. These implements include animal-drawn ploughs, cultivators and weeders. After green revolution, the use of tractors and tractor mounted implements started in Pakistan. Before the entrance to mechanized farming in Pakistan, on an average 7.5-22 ploughings were done before wheat planting in rain-fed areas of Punjab. Similar number of tillage operations was also recorded in rice-wheat cropping system of Punjab by different scientists. Number of ploughings in Khaber Pakhtunkhwa under maize-wheat cropping-systems is less (3-6). Repeated shallow cultivation are used to control weeds and to conserve moisture in irrigated areas of Pakistan but this practice has a disadvantage of creation of hard pan below the cultivated layer. Desi or local plough, meston plough, hindustani plough, sindhi plough and sarhadi hal are some traditional implements still used in different areas of Pakistan to manage the soil for crop production and weed control. Mouldboard plough is the most efficient tillage implement for seed bed preparation and weed eradication in Pakistan. Moreover, disk plough, chisel plough, subsoiler and rotavator are also useful primary tillage implements used by tractors. There are different types of harrows, cultivators and rollers used for secondary tillage practices. These are used for inter-culture, hoeing, thinning, earthing up and weeding.
Preventive method for weed control has been partially used in Pakistan but unfortunately our farming community is not much conscious about the weed seeds invasion through cultural operations. Scientists have reported that a large number of farmers used to sow weed infested seed through drills and planters. Cleaning, rouging and grading of seed are helpful in prevention of weed seed infestation. Crop rotation is also an effective tool being used by many farmers to control weeds. It minimizes and even eliminates different obnoxious weeds of rice-wheat, cotton-wheat and maize-wheat systems. Phalaris minor can be controlled if alfalfa is included in rotation. Many farmers in Pakistan are using successful rotations for better weed management. Alternate flooding and drainage, modified planting geometries, plant density maintenance, cultivar selection, planting time adjustment, mulching and proper mechanization of farm are some useful techniques which are being used in different areas of Pakistan.
Control measures-modifying with time:
Pakistani farmers are also using different hand tools like khurpa, kasola, daranti and kassi for manual weeding depending upon weed species and distribution. “Dab” or stale bed method is one of the oldest practices for weed control in Pakistan. In multiple cropping-systems, land is ploughed and planked by heavy “Sohaga” (Planker) about 2 weeks before sowing the wheat crop. This practice allows free germination of weed seeds up to 7-10 days which are destroyed by ploughing field again for wheat sowing. It gives good control over weeds. Farming communities of Pakistan prefer cultural and chemical methods of weed control because of small land holding, lack of capital investment and lack of technical skills. Cultural method is more common and effective in Pakistan as it is environment friendly and convenient for farmers. After a reluctant start, farming community of Pakistan has shifted towards the intensive use of chemical weedicides and herbicides. Gramaxone (paraquat) was the 1st herbicide registered in Pakistan and it was used in sugarcane and potato crops. A large number of pre emergence and post emergence herbicides are under use in different cropping-systems of Pakistan. Biological weed control is the method; least adopted in Pakistan and requires a lot of attention in future. So far, this approach has no significant results in agricultural crops of Pakistan but now a shift of mind set has initiated the use of different bioherbicides. Different crop extracts have been identified as potential bioherbicides. The extracts of sorghum, sunflower, brassica and many other crops and weeds have been successfully used for weed control at research level. The use of bioherbicides as weed control approach has bright future in Pakistan. Work on organic weed management through integration of different Allelopathic crop extracts and crop residues have also been started in Pakistan. It could be a better weed management option in different agro-ecological zones of Pakistan. Scientists in Pakistan are working on use of concentrated aqueous exudates of different plants for weed control in wheat crop.
Conservation tillage operations:
The trend of conservation tillage practices is also increasing in Pakistan. Conservation tillage also provides a specific set of environmental factors affecting weed populations. Weeds infestation in conservation tillage systems is a major concern and a key reason for reluctant approach of farmers towards its adoption. Conservation tillage is mainly focusing on minimal tillage with specific herbicide application for better weed control. The concept of zero tillage is being adopted at larger scale because of constraints in rice-wheat cropping-system. Farmers are growing their wheat crop by zero tillage to save the time of land preparation and to conserve the resources. Resource conserving techniques will be very effective and crucial in South Asian countries including Pakistan in near future as its population is increasing alarmingly and resources are static rather depleting. There are many other integrated approaches for weed control being used in Pakistan. The integration of cultural practices, mechanical methods, composting, irrigation, fertilizer management, crop rotation, mixed cropping, biological control and use of herbicides is recommended and being practiced for most of the common weeds present in Pakistan. Integration of chemical weed control and inter row cultivation in sugarcane field has given better weed control and higher yield. Integrated use of different types of natural and artificial mulches along with chemical herbicide and hand weeding gives good weed suppression in maize crop.
• Always prefer organic based weed management options rather than intensive use of chemicals.
• Develop crop rotations that help to control weeds through spatial and temporal differentiation in weed growth and dispersal.
• Focus alternative approaches like allelopathy rather than conventional outdated weed management tools.
• Integrated weed management plan must be devised for each and every farm.
• Weed management options should be chosen on the basis of agro-ecological conditions, climatic conditions.
• Quarantine measures to opted for seed import and export to avoid the invasion of alien weeds across the borders.
• Strategic planning is much needed to re-design the cropping patterns which would be more appropriate to weed control.
• Modern farming technologies and mechanization should be utilized to get rid of obnoxious weeds.
• Focused research on different aspects of weed science and technology aided by proper policy making and implementation should be done.
These are some weed control practices in Pakistan which are offering still a substandard weed control but can be improved by using judicial weed management plans. There must be an emphasis on integrated weed management and biological weed control methods to have a conserved and safe agro-ecological system. A lot of research is needed to identify the problematic weeds, their modes of dispersal, distribution and effects on crop production. Moreover, research should be done to explore the best combination of weed management practices under different climatic conditions. Comprehensive plans must be devised to control weeds keeping climatic conditions, resources availability, cropping-system and local agricultural practices in mind.
The writer is associated with the Department of Agronomy, Univ of Agriculture, Faisalabad, Pakistan.