Epidemiological development of Cercospora beticola (Sacch.) in sugar beet crops

Variation of predisposition influences the epidemiological behavior of Cercospora beticola. The results are gained from 57 instances (3 years, 3 locations, 6 sugar beet cultivars, 3 nitrogen degrees). The beginning of the epidemic progress, defined as an infection frequency of 50% beet plants in a natural sugar beet field, occurred from beginning to middle of July at the earliest, but ill most casts to the first and second decade of August. The shortest timespace from closing of sugar beer rows to the beginning of epidemics is calculated by 5 weeks, exceeded up ci, 7 weeks by highly resistant cultivars. Concerning the epidemic progress of the fungus, there Ire three successive phases. As a first disease stage, the horizontal distribution lip to a 100%, plant infection rare is considered, which in most cases needs 2-4 weeks hut may be extended up to 8 weeks in cases of resistant cultivars linked with unfavorable weather conditions. The horizontal distribution is followed by the vertical distribution from leaf to leaf as a second stage. Leaf infection rate increases strong, when 70% or more plants are infected. The vertical distribution is limited by a leaf infection rare of 60-80%. because younger leaves in the middle of the leaf remain free of infection. Necrosis remains under 1% of the leaf area during the first and second stage of disease progress. Leaf necrosis increases strong, when 60-80% of the leaves are infected. The third stage is characterized by increases of necrosis up to 15% of leaf area per week and at the end of the vegetation period, a maximum of 60% was evaluated, mainly under infection favoring conditions. From beginning of epidemics to the third stage, it needs 4-5 weeks at least. This fact is very important concerning the necessity of fungicide treatments. Leaf damage is highest to the middle leaf apparatus. The collection of data should support the development of a disease forecasting system.