A field of sorghum infested by Witchweed (Striga hermonthica) in Kenya. © University of Greenwich

Weeds form a ubiquitous component of agroecosystems. They contribute to substantial levels of crop loss in smallholder systems, particularly in the tropics and sub-tropics, where a combination of resource constraints at household level, difficult-to-control species, and often a poor understanding of crop/weed interactions complicate the development of sustainable control systems. In many farming systems of the developing world weed control is the most labour demanding pre-harvest operation, for example accounting for up to 60% of labour used for maize production in sub-Saharan Africa. Very often women and children shoulder much of this burden.

 

NRI weed scientists have many years' experience in characterising weed problems and researching appropriate management practices as components of cropping systems in developing countries in Africa, Asia and Latin America. Based at Long Ashton Research Station, this small group has developed extensive strategic links with cropping systems specialists in the international institutes and national programmes around the world. Recent major targets have included cereals in semi-arid areas of Africa, where the parasitic weed Striga is one of the main constraints to production, and rice for which changes in agricultural practice linked to population pressure lead to serious problems with grass and sedge weeds and to the evolution of herbicide resistance.

 

Removing wild rice (Oryza longistaminata) from a rice field in southern Mali. © University of Greenwich

The Group provides expertise in:

• Participatory research approaches to the development of weed control systems for small holder farmers
• Cultural control of perennial grasses
• Weed management in rice
• Improved fallows and cover crop legumes
• Identification of parasitic weed (Striga and Alectra) resistant sorghum and cowpea cultivars and development of integrated Striga management.
• Integration of herbicides in small holder cropping systems
• Management of herbicide resistant weeds
• Development of competitive cultivars
• Development and testing weeding practices in animal draught systems

Staff

Dr Charlie Riches

Projects

Integrated management of Striga species parasitic on cereals in East Africa (DFID in collaboration with University of Sheffield)

Control of wild and weedy rice in Africa (DFID in collaboration with WARDA)

Weed management in flood-plain rice in Bangladesh (DFID in collaboration with IRRI and Bangladesh Rice Research Institute)

Weed management in direct seeded rice on the Ganges Plain (DFID in collaboration with IRRI and GB Pant University)

Weed management in cotton in the Zambesi valley of Zimbabwe (DFID in collaboration with Silsoe Research Institute and University of Zimbabwe)

Tillage and weed control for wetland maize/rice systems in Zimbabwe (DFID in collaboration with Silsoe Research Institute and University of Zimbabwe)

Integrated weed management in rice in West Africa DFID collaboration with WARDA).

Publications

Kamal I. M., Musselman L.J., Riches C.R. (2001) The genus Striga (Scrophulariacea) in Africa. Annals of the Missouri Botanical Gardens 88: 60-103.

Valverde B.E., Charves L., Garita I., Ramirez F., Vargas E., Carimol J., Riches C.R., Caseley J.C. (2001) Modified herbicide regimes for propanil-resistant jungle rice control in rain-fed rice. Weed Science 49: 395-405.

Haefele S., Johnson D. E., Diallo, S., Wopereis M.C.S., Janin I. (2000) Improved soil fertility and weed management pays off for irrigated rice farmers of the Sahel, West Africa. Field Crops Research 66: 101-113

Kim D., Caseley J.C., Brain, P., Riches C.R., Valverde B.E. (2000) Rapid detection of propanil and fenoxaprop resistance in Echinochloa colona. Weed Science 48: 695-700.

Valverde B.E., Riches C.R., Caseley J.C. (2000) Prevention and management of herbicide resistant weeds in rice: Experiences from Central America with Echinochloa colona. San Jose, Costa Rica: Camara de Insumos Agropecuarios. pp 123.

Poliaszek A., Riches C.R., Lenne J.M. (1999) The effects of pest management strategies on biodiversity in agroecosystems. In: Wood D., Lenne J.M. (Eds.) Agrobiodiversity: characterisation, utilization and management. Wallingford: CABI Publishing. pp 273-303.

Twomlow S., Riches C., O'Neil D., Brookes P., Ellis-Jones J. (1999) Sustainable Dryland Farming in Sub-Saharan Africa. Annals of Arid Zone 38: 93-135.

Dingkuhn M., Johnson D. E., Sow A., Audebert A. (1999) Relationship between Upland Rice Canopy Characteristics and weed Competitiveness. Field Crops Research 60: 79-95

Becker M., Johnson D. E. (1998) Legumes as dry season fallow in upland rice-based systems of West Africa. Biology and Fertility of Soils 27: 358-367

Johnson D. E., Dingkuhn M., Jones M. P., Mahamane M. C. (1998) The influence of rice plant type on the effect of weed competition on O. glaberrima and O. sativa. Weed Research 38: 207-216

Dingkuhn M., Jones M. P., Johnson D. E.,Sow A. (1998) Growth and Yield Potential of Oryza sativa and O. glaberrima upland rice and their interspecific progenies. Field Crops Research 57: 57-69

Johnson D. E. (1997) Weeds of Rice in West Africa. West Africa Rice Development Association, Bouake, Côte d'Ivoire. 312 p. ISBN 92-9113-1105.

Johnson D.E. Riches C.R., Diallo R., Jones M.P. (1997) Striga on rice in West Africa: crop host range and the potential of host resistance. Crop Protection 16: 153-157.

Riches C.R., Twomlow S., Dhliwayo H. (1997) Low-input weed management and conservation tillage in semi-arid Zimbabwe. Experimental Agriculture 33: 173-187

Riches C.R., Knights, J.S., Chaves, L., Caseley, J.C., Valverde B.E. (1997) The role of pendamethalijn in the integrated management of propanil-resistant Echinochloa colona in Central America. Pesticide Science 51: 341-346.