Studies on the effects of stinging nettle extract, phosphoric acid and conventional fungicide combinations on the management of potato late blight and tuber yield in the Highlands of Kenya

Abstract

Efficacy of stinging nettle extract, phosphoric aci d and fungicides combinations was assessed for late bligh t control for two cropping seasons at Tigoni and Marimba loca tions in Kenya. Disease severity, relative area under dis ease progress curves (RAUDPC), pathogen lesions sizes an d numbers, and tuber yield were quantified during the 2008 and 2009 cropping cycles. The application of metala xyl alternated with phosphoric acid resulted in signifi cant suppressive effects on late blight. The average lat e blight severity ranged from 3.5 to 34% in 2008 and 4.7 to 50% in 2009 at Tigoni location. RAUDPC for the same locati on ranged from 5 to 40% and 5 to 50% in 2008 and 2009, respectively. Similar levels of late blight severit y have been recorded at Marimba locations. Lesion, growth/size and pathogen lesion numbers on potato plants differed significantly (p < 0.05) among treatme nts. However stinging nettle extract, phosphoric acid and fungic ides varied in late blight control. Potato tuber yield v aried among treatments. Phosphoric acid treatment had significantly (p < 0.05) greater tuber yield compar ed to those of metalaxyl at both locations. Field plots t reated with stinging nettle extracts resulted in the lowest tub er yield than the corresponding treatments with the exceptio n of the untreated control. Thus, stinging nettle extrac t, phosphoric acid, fungicides and their combinations can be readily effective in the suppression of late blight severity and pathogen lesions with moderate increases in tub er yield