Role of weather on <i>Alternaria</i> Leaf Blight Disease and its effect on Yield and Yield Components of Mustard

Abstract

Alternaria leaf blight disease caused by Alternaria brassicae in mustard (Brassica juncea (L)
Czern and Coss) was studied in two crop seasons, 1992 and 1993 in Nepal at Nawalpur, Sarlahi
(Tarai) and Khumaltar, Lalitpur (mid hill). At Nawalpur, epidemics of the disease was recorded for
both seasons. Weather conditions like humidity, temperature and frequent rainfall played key role
for the epidemics. In experimental fields, the disease appeared first in mid-December when the
relative humidity was more than 80% with maximum temperature ranging between 18-25°C and
minimum between 10-14°C. At Khumaltar, incidence of the disease was low in both seasons due to
low average temperature from December to February. Among cultivars, Krishna and Pusabold were
less susceptible than Varuna. Both mancozeb and iprodione had effectively reduced disease in the
sprayed plots and increased seed yield by 48% and 130% respectively. The correlation between
disease severity and yield, and yield components was negative and highly significant. Average yield
loss was estimated to be in the range of 32 to 57%. Seed infection was also significantly higher in
non sprayed treatment than sprayed one. The disease showed a negative effect on oil content causing
losses on oil between 4.2 to 4.5%.

Key words: Alternaria brassicae; epidemics; iprodione; mancozeb; mustard; oil content

DOI: 10.3126/narj.v6i0.3366

Nepal Agriculture Research Journal Vol.6 2005 pp.62-72