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Plantwise Technical Factsheet

cogon grass (Imperata cylindrica)

Host plants / species affected
Agave sisalana (sisal hemp)
Ananas comosus (pineapple)
Arachis hypogaea (groundnut)
Camellia sinensis (tea)
Cinchona
Citrus
Cocos nucifera (coconut)
Coffea (coffee)
Elaeis guineensis (African oil palm)
Ficus carica (common fig)
Glycine max (soyabean)
Gossypium hirsutum (Bourbon cotton)
Hevea brasiliensis (rubber)
Hordeum vulgare (barley)
Ipomoea batatas (sweet potato)
Manihot esculenta (cassava)
Musa textilis (manila hemp)
Musa x paradisiaca (plantain)
Oryza sativa (rice)
pastures
Saccharum officinarum (sugarcane)
Shorea robusta (sal)
Solanum tuberosum (potato)
Tectona grandis (teak)
Zea mays (maize)
Description

I. cylindrica is a perennial grass which varies in height (30-150 cm). The culms (above-ground stems) are short, erect and arise from rhizomes (underground stems). The rhizomes are tough, white, commonly 1 m long but can be considerably more, are extensively branched and covered with papery scale leaves at the nodes. Roots are fibrous, emerging from the base of the culm and the nodes on the rhizome. Leaves are stiff, linear-lanceolate, up to 120 cm long and 4-18 mm wide, with a prominent, off-centre, whitish midrib, scabrid margin and pointed tip. The ligule is an inconspicuous membrane. The inflorescence is a white, spike-like panicle, terminal, fluffy, 5-20 cm long and up to 2.5 cm in diameter. Spikelets are numerous, 3.5-5.0 mm long, each surrounded by a basal ring of silky hairs 10 mm long. The grain is oblong, pointed, brown and 1-1.5 mm long.

Prevention and control

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.

Physical/Mechanical Control

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.

Biological Control

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.’

Chemical Control

Many herbicides have been evaluated and used for the control of I. cylindrica (Brook, 1989; Townson, 1991). Of the four main products (dalapon, glyphosate, glufosinate and imazapyr) used in recent years, glyphosate has become the market leader. A typical high-volume application involves spraying glyphosate in 250-800 l/ha of water using knapsack or tractor-mounted equipment. There is scope for using low volume applications of <50 l/ha with very-low-volume and spinning-disc sprayers and also for the use of weed wipers. Nielsen et al. (2005) found little difference between knapsack and spinning-disc sprayers in effectiveness, but the knapsack was more economical on areas over 2 ha. Rope-wick applications was slightly less effective, but was the least expensive and most suitable for farmers without access to protective clothing.

Much effort has been given to improving the activity of glyphosate with formulation adjuvants (Townson, 1991). Proprietary additives, such as those based on tallow amines, are available for making tank mixtures with the herbicide, though reliable improvement in the performance of glyphosate in all situations cannot be guaranteed. The optimum time for applying glyphosate is when I. cylindrica is actively growing, with a large, green, leaf surface area. Cutting or burning the weed to encourage vigorous regrowth produces a good sward for spraying. A study by Lum et al. (2005) concluded that 150-200 g/ha of nicosulfuron applied at 1 or 2 weeks after planting maize gave effective control of I. cylindrica while significantly increasing crop yield.

IPM

After eradication of I. cylindrica, it is necessary to establish useful species which suppress regrowth of weeds and conserve soil fertility (Anwar and Bacon, 1986). Legume cover crops are widely advocated because of their smothering effect on weeds, stabilization of soil, fixing of nitrogen and ease of removal when the land is to be cropped. Calopogonium caeruleum, C. mucunoides, Desmodium intortum, Centrosema pubescens, Mucuna spp., Pueraria phaseoloides, P. triloba and Stylosanthes guianensis are examples of legumes that are used to rehabilitate I. cylindrica grassland or provide ground cover in plantation crops. For the small-scale farmer who is less inclined to use legume ground covers, intensive agricultural land use will prevent re-establishment of I. cylindrica.

Summary of invasiveness

I. cylindrica is a serious weed not only in crops but also in natural areas, causing serious economic and environmental damage. The ability of I. cylindrica to effectively compete for water and nutrients, spread and persist through the production of seeds and rhizomes that can survive a wide range of environmental conditions, and its allelopathic effects and pyrogenic nature, allow it to exclude native plant species and other desirable plants and dominate large areas of land.

Related treatment support
Plantwise Factsheets for Farmers
Kawooya, R.; Wetala, P.; Talwana, H.; Ogwang, J.; CABI, 2016, English language
 
Pest Management Decision Guides
Shamie, I. M. O.; Luseni, M. M.; Ngegba, P. M.; Koroma, M.; CABI, 2012, English language
CABI; CABI, 2017, English language
Kanteh, S. M.; Ndoleh, P.; Dimoh, G. J. S.; Luseni, S. J.; Koroma, F. M.; CABI, 2013, English language
Kawooya, R.; Wetala, P.; Talwana, H.; CABI, 2016, English language
 
External factsheets
BioNET-EAFRINET Invasive Plant Factsheets, BioNET-EAFRINET, 2011, English language
Rice Knowledge Management Portal Recap Sheets, Directorate of Rice Research, English language
IITA IPM Field Guides for Extension Agents, International Institute of Tropical Agriculture (IITA), 2000, English language
IITA IPM Field Guides for Extension Agents, International Institute of Tropical Agriculture (IITA), French language
Sweetpotato DiagNotes Fact Sheets, The University of Queensland, English language
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