Weed infestation in maize is one of the key factors responsible for the lower productivity and poor quality of produce. Reduction in grain yield is ranged from 33 to 50 per cent or even more depending upon the intensity and nature of the weed flora . The traditional method of manual and mechanical weeding is quite effective, but arduous, time consuming and highly costly. Under such situation, chemical weed control is a better option to conventional methods and use of herbicides forms an integral part of the modern crop production. In the last few decades different herbicides were used alone or in combination to eliminate the weeds but their efficiencies differ because of their narrow spectrum of weed control. In the recent years, the introduction of herbicide tolerant crops has transformed the way of chemical weed management method. Herbicide tolerant crops and their weed management systems allowed the use of broad- spectrum post emergence herbicides, which have reduced environmental impact.
These systems may reduce the use of soil applied residual herbicides and consequently reduce the potential for these herbicides to leach into ground water . Transgenic stacked hybrid maize was developed for preventing yield losses of maize crop due to pests and weeds and to improve productivity. The stacked maize crop having both insect protection and herbicide tolerant traits will provide protection to the crop from target pests and also provide tolerance to glyphosate herbicide. MON 89034 is second generation Bt corn technology effective against lepidopteron insect pests with a unique and innovative dual mode of action.The plants become tolerant to the herbicide while weed flora are suppressed after application of herbicide. These efficacious systems allow post emergence use of glyphosate for total weed management in glyphosate tolerant transgenic maize. In view of the importance of chemical weed control in herbicide tolerant transgenic maize, field experiments were conducted at Tamil Nadu Agricultural University, Coimbatore to evaluate the weed control efficiency and yield of transgenic stacked maize hybrids.Rice is one of the most important crops in the world.
More than 90% of the world’s rice is grown and consumed in Asia. In most Asian countries, rice is commonly grown by manual transplanting of seedlings into puddled soil . Recently, however, there has been a shifting of puddled-transplanted rice to seeded rice in many Asian regions. The main reasons for this shift are labor and water scarcities. The farm labor wage has in- creased significantly because of the migration of labor from rural to urban areas. In addition, it is difficult to acquire labor at the critical time of seedling transplanting. By the time labor is available, the critical time of trans- planting has already passed, which results in a decline in grain yield. Puddling and transplanting operations in the puddled-transplanted rice production system consume a considerable amount of water. It was predicted that South and Southeast Asia may experience physical and economic water scarcities in the near future . Therefore, to solve the problems of labor and water scarcities, farmers in many Asian countries are shifting toward seeded rice systems, especially mechanized sowing of dry-seeded rice . Seeded rice systems have several advantages over puddled-transplanted rice systems.
However, weeds are the number-one biological constraint to the production of seeded rice systems because of the absence of standing water at crop emergence to suppress weed emergence and the absence of a seedling size advantage to suppress weed growth . Rice cultivars capable of emerging under anaerobic conditions are not available in Asia and therefore fields can be flooded only after crop emergence . In Asia, the intensification of rice-based cropping systems has increased the production of crop residues and, in the absence of an effective residue management strategy, farmers burn crop residues in the field . Burning not only results in a loss of nutrients but also causes atmospheric pollution that poses a threat to ecosystem and human health . Many Asian governments have banned residue burning and other governments may soon follow . Crop residues can be used as mulch to suppress weed emergence and weed growth . Crop residues are usually retained in zero-till fields ; however, the residues can also be used as mulch after conventional tillage . This involves temporarily removing the residues from the field and then returning them to the field after crop planting. Many large farmers may not follow this practice, but this option may be more feasible for farmers with small land holdings .