Control of leaf spot disease caused by Cercospora sp on groundnut (Arachis hypogaea) using methanolic extracts of yellow oleander (Thevetia peruviana) seeds

A study was carried out in Yaounde (Cameroon) on two cultivars of groundnuts (Bafia var. and 55-437 var.) treated with methanolic extracts of Thevetia peruviana seeds (METPS), to evaluate the epidemiology of Cercospora leaf spots (CLS) and the antifungal potentials of these extracts under natural conditions. METPS were obtained by maceration of seed powder (0,33 kg/l) in methanol. Two concentrations of METPS (1.8 and 3.7 kg/ha), a benomyl and a control treatments were used in four replicates of a randomised block design. Disease severity, incidence, lesion size and yield were assessed. Two foliar applications of antifungal substances were effected at 15 days interval. The epidemic on both groundnut varieties was low in plots sprayed with METPS and benomyl when compared with the control. Disease incidence, lesion size and CLS severity were reduced to 37.25, 33.10 and 32.61 % respectively in plots sprayed with METPS compared to the control. The Bafia var. was more tolerant to CLS than the 55-437 var. Groundnut yield increased by 32.89 and 41.37 % for the Bafia var following applications of METPS and benomyl respectively. These results suggest that integrating host resistance and METPS efficiently protects groundnut against CLS.