Wj. Drepper et al., SYSTEMIC INFECTION OF DOWNY MILDEW ON MAIZE IN THAILAND AND THE EFFECT OF WEATHER FACTORS, Zeitschrift fur Pflanzenkrankheiten und Pflanzenschutz, 100(6), 1993, pp. 634-644
Seven epidemics of downy mildew on maize were monitored in holistic fi
eld trials on the cultivars 'CM 109' and 'SSDMR' in Thailand during 19
83-1985. In the susceptible cv. 'CM 109', practically all epidemics fo
llowed a monomolecular pattern reaching 100 % systemic disease inciden
ce. For the resistant cv. 'SSDMR', the curves are similar but at lower
intensity levels. In addition, in a sequential planting experiment th
e final incidence of systemic disease 6 weeks after planting was monit
ored for 34 epidemics. Their results show that daily mean temperature
had the greatest influence on systemic infection. High relative humidi
ty was ranked as the second most important factor for the epidemics. A
Gompertz function with two independent variables, 'daily mean tempera
ture' and 'mean daily number of hours with relative humidity above 90
%', was fitted to the incidence data of the two cultivars. For the mor
e susceptible cv. 'CM109', the coefficient of determination was 0.71,
temperature alone explained 64 % of the variation. In experiments unde
r controlled conditions, the incubation periods of systemics infection
s were determined. Under more or less constant temperatures, duration
of leaf wetness after infection was negatively correlated with the inc
ubation period of systemic lesions which ranged from 14.4 to 11.5 days
.