We are currently working on the impact of Striga and Rhamphicarpa fistulosa on rice yield losses in SSA using econometric models. The papers are under review and I may share with you when published.

A huge amount of seeds (40,000 – 90,000) can be produced by a single Striga plant . With the close biological association between Striga spp. and their host plants, and yield losses linked to the weed, Striga may have become the greatest biological constraint on food production in Africa, a more serious problem than insects, birds, or plant disease . Yield loss assessment due to Striga is complicated by the fact that significant damage is inflicted before the parasite emerges from the soil. Many authors.  have recognized that Striga is widely spread and is difficult to control by a single measures. The need for an integrated control approach (host plant resistance, cultural practices, and chemical treatments) was therefore stressed. An integrated management approach, if properly designed, using a combination of control measures has the potential to provide a lasting solution to the Striga problem.

Losses in grain yield inflicted by the parasite are difficult to estimate (as significant damage is inflicted before the parasite emerges). The damaging effects of the parasite are influenced by a multitude of variables including inherent sensitivity of the host plant, climatic conditions and the level of infestation (Sauerborn, 1991; Obilana and Ramaiah, 1992; Butler, 1995). The effects of individual Striga plant is small, 1,000 plants per hectare appearing above ground cause a grain yield reduction of only about 2 to 3 kg/ha (Doggett, 1965). However, an average of 5-15% losses in yield is often quoted for low infestations (Kim et al., 1994). The magnitude of the loss in yield due to the parasite is determined by the level of Striga infestation, soil fertility, agro-climatic conditions, land use system, the plant species and the host genotype (Oswald and Ransom, 2004). In East Africa, Doggett (1965) reported 59% loss in grain yield for susceptible sorghum cultivars. In West Africa, the reported losses in grain yield were 5% for resistant, 95% for susceptible and 45-63% for tolerant sorghum cultivars (Obilana, 1983; Obilana and Ramaiah, 1992). However, in view of the high fecundity and accompanying mismanagement, large Striga populations rapidly build up from incipient infestations and complete crop failure soon ensues under conditions conducive to establishment and proliferation of the parasite (Ejeta et al., 1993; Riches and Parker, 1995).

In general, the estimated annual cereal grain losses associated with Striga across Africa is about 4.1 million metric tones (Sauerborn, 1991). In monetary terms the annual losses in crop revenues inflicted by the parasite in West Africa, alone, were estimated to be between US$ 28 million and US$ 12.8 billion (Ramaiah, 1984; Mboob, 1989). Striga also causes indirect losses comprising changes in production strategies, land abandonment and in extreme cases human migrations in response to heavy infestations (Obilana and Ramaiah, 1992). Similarly Striga infestation affects labour supply patterns as a Striga-specific weeding is often required. Unlike the effects of Orobanche species the observed reductions in host growth and yield caused by Striga cannot be explained by direct competition for carbon and nutrients (Mazaheri, et al., 1991; Barker et al., 1996; Hibberd et al., 1998; Gurney et al., 2000).

Dear Dr Hassan,

Many thanks for your answer and for the article that I found very interesting.

Best regards