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Brook (1989) and Townson (1991) summarized control methods in their reviews of I. cylindrica. IRRI/NRI (1996) produced a practical guide to the management of I. cylindrica by smallholder farmers in South-East Asia and a companion volume on grassland rehabilitation using agroforestry and assisted natural regeneration has been produced by ICRAF (1999). Mechanical and/or chemical control are the principal components of any strategy to manage I. cylindrica. At present, there is no scope for biological control with pathogens or predators.
Successful mechanical control of I. cylindrica necessitates destruction of the capacity to regrow after treatment, usually by physical damage, burial or complete removal, or to inhibit growth of the weed so severely that it ceases to be a problem. In bad infestations, this requires the management of a large biomass. The rhizomes alone can have fresh weights of 40 t/ha reaching depths of 1 metre or more in the soil, and have millions of viable buds with the potential to re-infest land if control is less than complete. In practice, such complete control is virtually impossible but mechanical control has been, and remains, one of the most widely used methods of managing I. cylindrica, either as a stand-alone treatment or as an integrated technique with other methods.
The main method of control practised by smallholder farmers is to slash or hand weed. Bush burning is a common feature of fields in the moist savannah of West and Central Africa but it enhances seed production. Clearing land of I. cylindrica with a hand hoe can require 85 man-days/ha. In West Africa, farmers generally weed maize fields infested with I. cylindrica five times to minimize yield reduction by this weed. For larger areas of land, soil cultivation by tractors is more appropriate, best done during the dry season when most of the plant’s biomass is in the rhizomes and when desiccation is most effective. Timing of cultivation is critical, as if done in the wet season, not only is it difficult but there is insufficient sunshine to kill the exposed rhizomes, and regrowth soon occurs. A typical sequence of operations is to burn off the Imperata, disc plough the field to a depth of 30-40 cm, leave for at least 2 weeks, then plough again at right angles to the previous direction. The field is then harrowed twice at an interval of about 2 weeks. ‘The integration of deep ridging, deep hoe weeding and shading suppressed speargrass more effectively than farmers' practices’ (Vissoh et al., 2008).
Grass pressing (i.e. lodging, rolling) is a simple, low-cost technique that is used to control the growth of I. cylindrica. It can be used to clear areas for planting and as part of an integrated approach to enable the establishment of legume ground covers (IRRI/NRI, 1996; ICRAF, 1999). When pressing, it is important that grass shoots are only pressed down, i.e. bent or crimped, like folding a plastic water hose. If shoots are broken, as in cutting or burning, then rapid shoot development results. With pressing, dense stands of I. cylindrica can have regrowth decreased by 40-80%. As much as 90% of pressed I. cylindrica decomposes or dries up within 1 month and it can take more than 6 months for the regrowth to reach its previous population density (Anon, 1989). The best growth stage to press I. cylindrica is when it is about 1 metre high, because stems usually remain permanently bent after being pressed. Appropriate equipment to use includes logs which are rolled over the Imperata and planks held by rope or wooden handles which the operator stands on, lifts, moves and repeats the process over the area to be pressed.
Ivens (1980) was sceptical about the potential for biological control of I. cylindrica due to its worldwide distribution and its regenerative capacity. However, there has been a search for organisms which can be used for classical or augmented control. A selection of these is given in the list of natural enemies, but no fully effective means of biological control are yet available. Yandoc et al. (2005) tested the fungi Bipolaris sacchari and Drechslera gigantean in greenhouse and field and concluded ‘the level of injury caused by these fungi is sufficient to support their use as components for integrated management of cogongrass.’
Due to the variable regulations around (de-)registration of pesticides, we are for the moment not including any specific chemical control recommendations. For further information, we recommend you visit the following resources: