Managing Weeds of Rice in Africa

In sub-Saharan Africa (SSA), weeds are estimated to account for rice yield losses of at least 2.2 million tonnes (Mt) per year (Rodenburg and Johnson, 2009). Combined with costs of weed control, the financial losses easily surpass half the cost of current regional rice imports. If not controlled, weeds cause yield losses in the range of 28–74% in transplanted lowland rice, 28–89% in direct-seeded lowland rice and 48–100% in upland rice (Rodenburg and Johnson, 2009). In West Africa, it has been shown that farmers can increase their rice yields by 15–23% by applying relatively basic measures to improve weed control, such as bunding of fields to retain flood water, and timely interventions such as herbicide applications and hand weeding (e.g. Haefele et al., 2000; Becker and Johnson, 2001b; Becker et al., 2003). African farmers do not, however, perceive weeds as solely undesirable. Many species often considered as weeds also feature in traditional pharmacopoeias (e.g. Stepp and Moerman, 2001) or are collected for domestic use, crop and postharvest pest control functions or as an additional source of food (Rodenburg et al., 2012). Introduction