Leersia hexandra (southern cut grass)

The choice of control method depends upon the size of weed infestation, the cost of labour, the value of the crop, and the cost and availability of herbicide.Methods that are commonly used to control perennial grasses and that can be used for L. hexandra include: preparation of a clean seedbed; rotation of rice with lowland, non-irrigated crops; tillage methods, i.e. ploughing, to destroy rhizomes; and applications of systemic herbicides, such as glyphosate, with attention to the selectivity of the herbicide: for example, if the crop is susceptible to glyphosate then apply it pre-planting (Ampong-Nyarko and De Datta, 1991).Other methods that have proved useful in the control of weeds in wetland rice are: closer row spacing to increase crop competition; thorough hand weeding; and burning stubble during the dry season (Moody, 1982).

Glyphosate (pre-planting and post-emergence), fenoxaprop-ethyl (post-emergence), fluazifop-butyl and fluazifop-P-butyl (post-emergence) and imazapyr (pre- and post-emergence) may be used for control. Rates of application will vary depending upon the crop and the timing of application: for a full description of weed control in rice, see Ampong-Nyarko and De Datta (1991). See also Soerjani et al. (1987) for further information on chemical control in Malaysia.

RiceA range of control methods is used in the management of weeds in rice. The following descriptions illustrate the factors that are important for weed control in wetland rice systems. The list is not comprehensive: for further details, see Ampong-Nyarko and De Datta (1991).Land PreparationLand preparation is important in all rice cultivation and contributes to good weed management. Methods used will vary according to the crop system, especially concerning the management of perennial weeds. In transplanted rice, ploughing and puddling to destroy weeds and incorporate them into the earth provide a major source of weed control. In dry-seeded wetland rice and direct-seeded rice, land is prepared by ploughing and is kept weed-free before use, either by hand weeding or by herbicide application. Use of herbicides will be determined by the water management of the cropping system: for instance, in dry-seeded rice, after land preparation, weeds are allowed to emerge and are then destroyed either by shallow cultivation or with a non-residual contact herbicide, such as paraquat; in transplanted rice, puddling is followed by a pre-planting treatment with glyphosate on emergent weeds. In dry-seeded wetland rice, a pre-planting herbicide, such as glyphosate, or a pre-crop-emergence herbicide, such as imazapyr or fenoxaprop, could be used. CultivationTaller rice cultivars with more tillers shade out weeds and reduce weed competition. Rotation of rice with other crops, such as jute (Corchorus sp.), can be important in reducing the build-up of large populations of perennial grass weeds. SpacingRice planted with close spacing (e.g. 15 x 15 cm) will shade weeds and reduce competition, while still allowing some mechanized weed control if required (Moody, 1982).Hand WeedingAdditional hand weeding is usually done early in the season, during the critical period and, if weed populations are high, then later hand weeding is a common practice. If labour is scarce, herbicides such as glyphosate, applied locally to weeds only, or bensulfuron or fenoxaprop are used. Hand weeding alone can give as good weed protection as herbicide use: for example, in rice that is direct seeded onto wet soil, seeds are sown onto a weed-free field and two or three timely hand weedings are sufficient to ensure optimum yields (Moody, 1982; Ampong-Nyarko and De Datta, 1991).SugarcaneCultivation followed by hand weeding has been shown to give sufficient control of L. hexandra in sugarcane (Keya, 1980).