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

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