The present study was carried out at Gemmeiza Agricultural Research
Station at EI-Gharbiya Governorate. Egypt in two successive growing seasons of
potato '(Solanum iuberosum, cv Diamant) as a host plant for Altemaria solani causing
the early blight disease. The study included a laboratory and field experiments. In
vitro results showed that Champion was the most potent as it had ICso of O.37ppm
while Koruse had the least effect (ICsa value of 5.65ppm). Potassium had a negligible
toxic effect in comparison with the used fungicides where its ICsa was 20.98ppm. The
co-toxicity factor (CTF) indicated that K combinations with the used fungicides
acquired synergistic or additive effects towards the fungus. The severity of early
blight disease in potato plants under the field conditions decreased greatly by the
doses than the half doses of the used fungicides. Combining K with the fungicides
reduced the disease severity especially with the doses of fungicides. Application of K
combined with the tested fungicides caused marked increase in potato tubers yield as
compared with the control. This may be due to the reduction of early blight disease
incidence as indicated from the disease severity. In addition. the enhancement for
vegetative growth was reflected greatly on the tubers crop of the plant. Potassium
increased the fungicides half doses actual effectiveness to be equal or higher than
that of their doses. Commercially. K combination with the used fungicides could be
used to decrease both controlling costs of the disease and environmental pollution.
The study recommends a potassium foliar spray at the time of fungicides application
for increasing their effectiveness on the disease control and on the host plant growth
and yield.