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 acid and fungicides combinations was assessed for late blight control for two cropping seasons at Tigoni and Marimba locations in Kenya. Disease severity, relative area under disease progress curves (RAUDPC), pathogen lesions sizes and numbers, and tuber yield were quantified during the 2008 and 2009 cropping cycles. The application of metalaxyl alternated with phosphoric acid resulted in significant suppressive effects on late blight. The average late blight severity ranged from 3.5 to 34% in 2008 and 4.7 to 50% in 2009 at Tigoni location. RAUDPC for the same location ranged from 5 to 40% and 5 to 50% in 2008 and 2009, respectively. Similar levels of late blight severity have been recorded at Marimba locations. Lesion, growth/size and pathogen lesion numbers on potato plants differed significantly (p < 0.05) among treatments. However, stinging nettle extract, phosphoric acid and fungicides varied in late blight control. Potato tuber yield varied among treatments. Phosphoric acid treatment had significantly (p < 0.05) greater tuber yield compared to those of metalaxyl at both locations. Field plots treated with stinging nettle extracts resulted in the lowest tuber yield than the corresponding treatments with the exception of the untreated control. Thus, stinging nettle extract, phosphoric acid, fungicides and their combinations can be readily effective in the suppression of late blight severity and pathogen lesions with moderate increases in tuber yield.