progressive pattern of powdery mildew disease in sugar beet fields in isfahan province

sugar beet cultivation is of great importance in isfahan province. powdery mildew is a major limiting factor to sugar beet. to evaluate powdery mildew status in sugar beet fields, samples were collected from main sugar beet growing areas including, isfahan, semirom, farydan and komsheche during 2009-10. in order to determine the disease severity, in each region, samples were taken at six growth stages from 10 fields. disease severity was measured based on 0 -100 scale. results showed significant difference among fields in each location in relation to disease severity. the highest rate of disease was found in isfahan and semirom with 50.30 and 46.31%, respectively, whereas in komsheche and freydan it was 18.94 and 14.44%, respectively. in all studied regions, the disease progress began from first week of august and reached to its maximum level in the first week of september up to first week of october in isfahan. in fraydan, semirom, and komsheche, the maximum level was recorded in september, early september, and last week of september, respectively. the disease severity continued up to last week of october in almost all regions. the sexual stage was observed as black points (cleistothecium) at the last stages of the growth. miscroscopic studies confirmed the production of ascospores in the region.