1988 Volume 54 Issue 2 Pages 198-203
It was shown by inoculations that ascospores of Sclerotinia sclerotiorum invaded the sunflower head mainly through florets with a period of 10 to 24 days from infection until the first visual symptoms appear under summer condition. In the field, numerous apothecia were found on the ground during late July to early August. No apothecia were detected in September. The occurrence of head rot closely correlated with number of apothecia appearing in the field at the flowering time of sunflower; frequency of head rot was higher when a lot of apothecia were observed at the flowering time of sunflower (40 apothecia/m2, 27% plants affected with head rot at Naganuma field), while it was only slight when few apothecia were observed (2 apothecia/m2, 2% plants affected with head rot). The difference of the flowering time accounted for the difference of disease incidence among 11 sunflower cultivars tested; the significantly different disease incidences were observed between early flowering group and late flowering group. The head rot was effectively controlled by spraying the fungicide vinclozolin (500 ppm a.i.) five times at 2 to 3 days intervals during late anthesis stage. The amount of sprays was 250 liters/1, 000m2.