But if flooding is reduced, other ways of controlling the weeds will be necessary. Chemical herbicides are becoming less socially acceptable as a result of public concern about health hazards, and some weeds are developing herbicide resistance, so new methods of weed control will have to be sought. One way is integrated weed management. Scientists are now examining the place of weeds in the entire rice-growing system, with the aim not simply of attacking and killing them by one means or another, but of managing them in a way that will not interfere unduly with rice production. It also involves investigations of naturally occurring pathogens of weeds, and how they might be used to suppress weed growth.
Biotechnology offers promise .
In some 22 million ha of lowland and deepwater rice areas of the world, flash flooding leads to submergence of the plants. Submergence tolerance is appropriate to rainfed lowland areas where flash flooding lasts only for about 14 days, during which plants may become either partly or completely submerged. Elongation, on the other hand, is appropriate to areas where flooding is deep and lasts for several months. Details of some other ways in which biotechnology is helping sustainable rice production are given later in this Chapter. The International Irrigation Management Institute in Sri Lanka has been designated as the convening center for this initiative.