PHYTOPATHOLOGY M. Ndiaye et al. (2007) Phytoparasitica 35(4):392-400 Combined Effects of Solarization and Organic Amendment on Charcoal Rot Caused by Macrophomina phaseolina in the Sahel M. Ndiaye, *'1 A.J. Termorshuizen2 and A.H.C. Van Bruggen 3 The effects of soil solarization combined or not with millet residues or paunch contents amendments, on the survival of Macrophomina phaseolina (Tassi) Goid. and development of charcoal rot of cowpea (Vigna unguiculata), were assessed in a naturally infested soil. Solarization increased the soil temperature to 50~ for at least 4 h per day during June, leading to a significant reduction (44%) in soil inoculum of M. phaseolina. Paunch contents or millet residues amendment (3 t ha -1) caused 16% or 35% reduction of initial inoculum density, respectively. The combination of paunch contents or millet residues amendments followed by solarization, resulted in the strongest effects on inoculum density, with reductions of 46% or 66%, respectively. The reduction in disease severity, as expressed by the area under the disease progress curve, was 78% or 96% for the combination of millet residues or paunch contents amendments and solarization, respectively. The stronger effect of the treatments on disease severity than on inoculum density may be explained by a weakening effect caused by the treatments on the remaining inoculum. Our results suggest that in the Sahelian zone the combination of solarization and organic amendment can be a credible alternative to pesticides for managing charcoal rot disease and improving cowpea yield in fields with heavy infestations with M. phaseolina. KEY WORDS: Charcoal rot disease control; cowpea; millet residues amendments; Niger: paunch contents amendments; Senegal; Vignaunguiculata. INTRODUCTION Cowpea (Vigna unguiculata) is the main pulse crop of the semi-arid zone of the Sahel, but grain yields are usually as low as 200-300 kg ha -1 (28). Many factors contribute to the low yield including shortage of nutrients, and vulnerability to drought and to attack by pest and disease organisms (26). Potential solutions are available to solve partially the major constraints, except for the parasitic weed Striga and the fungal soilborne plant pathogen Macrophomina phaseolina (Tassi) Goid., which causes charcoal rot or ashy stem blight of cowpea and many other crops (5,9). In Senegal and Niger, heavy soil infestations of M. phaseolina occur widely, usually resulting in total crop lhilure when cowpea is grown, The pathogen is able to persist in the absence of hosts for several years (8), and therefore additional measures are needed to manage this pathogen. Received Nov. 7, 2006; accepted April 4, 2007; http://www.phytoparasitica.org posting Aug. 5, 2007, 1AGRHYMET/D6partementde Formation et de Recherche, Niamey, Niger. *Correspondingauthor [Fax: +227- 20315435; e-mail: m.ndiaye@agrhymet.ne;mbaye.ndiaye@wur.nl]. 2Biological Farming Systems Group, Wageningen University; current address Blgg, 6709 PA Wageningen, the Netherlands [e-mail: aad.termorshuizen@blgg.nl]. 3Biological Farming Systems Group, Wageningen University, 6709 PG Wageningen, the Netherlands [e-mail: ariena.vanbruggen @wur.nl]. 392 M. Ndiaye et al.