2.2.14
CHANGES IN THE OCCURRENCE OF SUGAR BEET VIRUSES IN MIDDLE GERMANY IN RECENT DECADES

G PROESELER1, E SHLIEPHAKE1, P RUECKER2 and H HARTLEB2

1Institute for Epidemiology and Resistance of the Federal Centre for Breeding Research on Cultivated Plants Aschersleben, Germany; 2 Plant Protection Service of Saxonia-Anhalt Magdeburg, Germany

Background and objectives
In the former German Democratic Republic the viruses of sugar beet were very important during the 1970s and 1980s. In the districts of Magdeburg, Halle and Leipzig especially, the occurrence of beet mild yellowing luteovirus (BMYV) and beet yellows closterovirus (BYV), and also beet mosaic potyvirus (BMV), were very high. Many sugarbeet plants showed typical virus symptoms in these regions in September. Very early infection from the end of May until the middle of July, particularly by BMYV and BYV (in addition to other factors) caused important losses of yield. In addition to agronomic measures, chemical control of aphids (especially Myzus persicae and Aphis fabae as virus vectors) was used on the basis of a prognosis system. The most important factor in this situation was the high concentration of fields of Beta vulgaris not only for the production of sugar but also for the production of seeds. The recommended distance of 3000 m between fields for seed and sugar production was insufficient and often unrealistic [1].

Results and conclusion
After the reunification of Germany the agricultural situation changed fundamentally and the production of seeds of B. vulgaris now takes place in the countries of southern Europe. The degree of infestation in September was reduced from a mean of 51% from 1980 to 1990 to 2.5% from 1991 to 1997. We believe that this is the main reason for the drastically reduced occurrence of yellows viruses, in addition to agronomic changes such as seed treatment with insecticides and new cultivars. Comparison of the flight activity of aphids since 1985 by a Rothamsted suction-trap at Aschersleben shows no differences. Although there are are great variations between the years in the totals of the two vector species trapped M. persicae and A. fabae), changes between the years 1985 to 1990 and 1991 to 1995 are generally not detectable [2]. No trends for a later or earlier presence of the first aphids trapped could be observed. Furthermore, oilseed rape is not a host plant of BMYV.

References
1. Fritzsche R, Kleinhempel H, 1984. Nachrichtenbl. Pflanzenschutz DDR 38, 25-29.
2. Schliephake E, Karl E, 1995. Beobachtung des Blattlausfluges mittels Saugfalle. Mitteilungen der Deutschen Gesellschaft fur Allgemeine und Angewandte Entomologie 10, 203-206.