Weeds and Weed Management in India - A Review

India has a wide range of agroclimates and soil types. The highly diverse agriculture and fanning systems are beset with different types of weed problems. Weeds cause 10-80% crop yield losses besides impairing product quality and causing health and environmental hazards. Invasive alien weeds are a major constraint to agriculture, forestry and aquatic environment. Crop-specific problematic weeds (weedy rice in rice) are emerging as a threat to cultivation, affecting crop production, quality of product and income of farmers. Traditionally, weed control in India has been . largely dependent on manual weeding. However, increased labour scarcity and costs are encouraging farmers to adopt labour and costsaving options. These include herbicides whose market grew at an annual rate of 15%. Integrated weed management (IWM) is being practiced by Indian farmers, with the level of adoption varying from one farm to the other. The continuous application of isoproturon coupled with mono-cropping rotation of ricewheat has led to the evolution of resistance in Phalaris minor Retz. In the northern part of India. Efforts to manage herbicide resistance have led to the adoption of conservation agriculture in the rice-wheat cropping system, as a component of IWM. Research on weed management in India is mostly centred on herbicide efficacy. Herbicides, applied alone or in combinations, have been regarded as essential tools in the effective management of weeds in different-ecosystems. IWM, which includes preventative, mechanical, cultural, chemical and biological methods, is advocated in crop production systems as well as aquatic and forest ecosystems. Herbicideresistant (HR) transgenic crops have the potential to improve the weed management efficiency and facilitate adoption of CA in India, provided the risks associated with such crops are examined in detail, prior to their adoption and commercialization. Newer weed management approaches must be developed considering the threat of HR weeds appearance in addition to the recurrence and persistence of weeds and the need to bring down weed management costs to enhance profit for farmers while protecting the environment. Understanding weed-ecology and-biology_and.using_infoimatioxLtechnoiogy, should be part of developing and disseminating effective, economical and ecologically advantageous IWM strategies in India. Detailed review of weeds and weed management' options of the past, present and future in India is made in this chapter.