STRIGA INFESTATION AND MANAGEMENT IN EAST AFRICA Paul L. Woomer, George D. Odhiambo and Canon N. Savala FORMAT, P.O. Box 79, The Village Market, Nairobi, Kenya Email: plwoomer@gmail.com ABSTRACT Striga hermonthica and S. asiatica are plant parasitic weeds of maize that cause widespread food insecurity. A review of available information on striga was conducted, and a database developed to assess the coverage, intensity, yield decline and economic loss of striga infestation throughout East Africa. The parasite has infested approximately 446,000 of the 3.84 million ha of maize cropland in East Africa (12%), reducing maize grain yields by 385,000 tons per year and causing economic losses of US $56 million yr -1 . The problem is greatest in Kenya (217,000 infested ha), followed by Tanzania (164,000 ha) and Uganda (65,000 ha) and is most severe in the Lake Victoria Basin and surrounding midlands. Maize fields in west Kenya contain an average 161 million striga seeds per ha that form 133,000 shoots ha - 1 within a maize field. For several decades, small-scale farmers sought to control striga by hand weeding, but this practice failed because striga causes damage before emerging aboveground. Two new technologies offer greater control of striga, 1) imazapyr seed coating of herbicide-resistant maize seeds, and 2) intercropping or rotation of maize with field legumes that suppress striga. On-farm testing of these technologies in west Kenya resulted in yield improvement of 785 and 545 kg maize grain per ha, and reduced striga expression by 84% and 71%, respectively. Striga infestation and its reduction through crop management are important, and often overlooked as determinants of soil health. Scientists with interests in land characterization and soil ecology are encouraged to incorporate striga management into their studies. Keywords: herbicide resistance, IR maize, parasitic plants, seed bank, soil health, witchweed INTRODUCTION Striga is a parasitic plant that originates from African grasslands but has now invaded vast areas of its cropland. Native grasses and traditional African cereals have some resistance, but most domesticated cereals have little or no ability to fight off the parasite. Germinated striga seeds infect host roots, feeding on the plant below-ground for several weeks, and then a fast growing shoot emerges that produces prolific flowers and thousands of tiny seeds (Odhiambo and Woomer, 2005). Host plants exhibit a range of symptoms including severe stunting, twisted growth and bronzing, and severely infested plants produce little or no yield. Two species of the parasite affect cereal crops in Africa, Striga hermonthica, with lavender flowers and common in East and West Africa, and in the Sahel, and S. asiatica, with red flowers that has colonized croplands in Southern Africa (Mohamed et al., 2001).