Trap crops of Striga hermonthica:: in vitro identification and effectiveness in situ

The parasitic weed Striga hermonthica is a major yield-reducing factor for cereal crops in savannah regions in Africa. This applies in particular to agro-ecosystems where a high human population density imposes a strong pressure on arable land. In these areas rotation with a leguminous trap crop is an attractive control method. Effectiveness of root exudates from varieties of cowpea (Vigna unguiculata), groundnut (Arachis hypogea) and soybean (Glycine max), on germination of S. hermonthica seeds were assessed in vitro. In addition, a 2-year study on effectiveness in situ was conducted with cowpea variety IT 90k-56 identified in vitro as a potential trap crop. Furthermore, cowpea variety TVX 1850-01F also identified in vitro as a potential trap crop, was tested on-farm. Results indicated that effectiveness of root exudates depends on Striga seed population and it is recommended that geographical origin and host crop of S. hermonthica, period of the year, as well as age of seeds be taken into consideration for identification of potential trap crops. There was no significant difference in Striga infestation of maize in 1995 if sowing of cowpea variety IT 90k-56 had been carried out on June 3 (early sowing), June 20 (intermediate sowing) or July 5 (late sowing) in 1994. However, plots where maize was grown in 1995 after they had been maintained as weed-free-fallow in 1994 showed significantly higher Striga infestation than plots where during previous year early sowing of trap crop had been undertaken. Maize grain yields in 1995 were significantly higher after trap cropping in 1994, regardless of sowing date, compared to weed free fallow plots. On-farm evaluation of cowpea variety TVX 1850-01F showed good results, reducing incidence of S. hermonthica on maize to nearly undetectable level after one season rotation. (C) 2003 Elsevier Science Ltd. All rights reserved.