Evaluation of aqueous neem (Azadirachta Indica A. Juss) kernel extract and thiophanate-methyl for the control of early and late leaf spots of groundnut (Arachis Hypogaea L.)

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Three different concentrations of aqueous neem kernel extract (15%, 20% and 25%; w:v) and thiophanate methyl ( Topsin _MR 70 WP at 700g/ha) were evaluated for their effectiveness in controlling early and late leaf spot diseases (caused by Cercospora arachidicola and Phaeoisariopsis personata, respectively ) of groundnut at Fumesua and Kwadaso both in the Ashanti Region of Ghana. Plants were sprayed twice i.e. 30 and 45 days after planting. The statistical analysis of the data on leaf spot incidence showed no significant differences among treatments. However, there were significant differences among the treatments with respect to disease severity. Topsin-MR was comparable to 25% neem kernel extract treatment in terms of disease suppression in the majority of the variables, viz, percentage defoliation, dry groundnut pod yield, kernel weight at Fumesua and percentage defoliation and dry groundnut haulm yield at Kwadaso. Although, these two treatments had equal efficacy, higher yields were observed from Topsin-MR treatment. These two treatments with the lowest mean disease severity were significantly different from the rest of the treatments. The lowest pod and haulm yields and greatest defoliation were observed in the treatments with the highest mean disease severity of early and late leaf spots. There was little difference between the 1 5%, 20% neem kernel extracts and the untreated but not significantly. Higher yields were obtained at Kwadaso than Fumesua regardless of higher disease severity levels.
A thesis submitted to the Board of Postgraduate Studies, Kwame Nkrumah University of Science and Technology, Kumasi, in partial fulfilment of the requirement for the award of the Degree of Master of Science in Crop Protection, 1998