Effects of NPK fertilizer and fungicide application rates on the performance and management of late blight (Phytophthora infestans) in irish potatoes (Solanum tuberosuml)

Abstract

Food insecurity has been an issue in developing nations worldwide including Kenya. This is as a result of soil related problems, climate change, crop pests and diseases among food crops. Late blight disease caused by Phytophthora infestans in Irish potato (Solanum tuberosum L) is a major challenge among the small-scale farmers in the highlands of Kenya. Yield losses as a result of late blight in Kenya are about 40 - 50%. The appropriate use of fungicides and fertilizers application rates is an option in the management of late blight. The objectives of this study were to determine effects of N:P:K 17:17:17 fertilizer and Acrobat MZ fungicide (Dimethomorph 90g/Kg + Mancozeb 600g/Kg) application rates on the incidence, severity of late blight and growth parameters of irish potato varieties. The experiments were carried out in a randomized complete block design both at Egerton University, field 7 and Tumaini farm, Molo. Inoculation of the crop with P. infestans was done at the vegetative stage. The treatments rates were fertilizer at 0, 90 and 135 KgHa -1, fungicide at rates of 0, 2.5 and 3.5g/L and two potato varieties (Kenya sherekea and Dutch robjin). Fertilizer was applied during planting while fungicide started at 37 days after planting (DAP) and repeated after seven days interval up to 61 DAP. Data collection was done at 47, 54 and 61 DAP on the number of leaves, haulms, height, percentage disease severity index (PDSI) and disease incidence (PDI) while yield was recorded 120 DAP. Data was subjected to analysis of variance (ANOVA) and treatment means were separated using Least Significant Difference (LSD) test. There were significant (P≤0.05) differences among the varieties and sites for disease development on application of fertilizer and fungicides. Results indicated that fertilizer and fungicide application rates had interrelated effects on late blight development. Total tuber yields significantly (P≤0.05) increased in all fungicide treated plots. The correlation matrix showed that total yield had significant and positive correlation with the site (r = 0.61), plant height (r = 0.51), number of leaves (r = 0.40) fungicide (r = 0.49) and fertilizer (r = 0.39). Irish potato variety had significant (P≤0.05) effects on both yield and disease development at Egerton University and Molo sites.