Befallsauftreten und Kontrolle pilzlicher Pathogene unter Bemessung des Fungizidpotentials in Bayern (English shop)

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In two-year field trials (2004/2005, 2005/2006), the occurrence of pathogen infestation in winter oilseed rape was recorded at four sites in Bavaria. Epidemiological, growth-regulatory and yield-related effects of fungicide application at differentiated timings (autumn, spring, early flowering, flowering, combinations) were analysed.

The dominant pathogen species was Phoma lingam, the causal agent of phoma stem canker; site-specific differences in disease occurrence could be demonstrated. An autumn treatment with fungicides showed a very high efficacy potential with a pronounced, significant reducing effect on the disease severity (DS), which had to be classified as high, on the oilseed rape leaves. At the root collar of the oilseed rape plants, Phoma lingam was detectable only with a delay; appreciable damage symptoms did not occur before flowering. Within a few weeks during ripening, infestation in the untreated control rose to maximum disease values of 7.2 (2004/2005) and 6.9 (2005/2006) respectively at the final assessment. Among the fungicide treatments, strategies including an autumn application (A/AS/ASF) showed the strongest disease-reducing effect at the root collar. Spring applications (S/AS/ASF) provided the strongest fungicidal control of Phoma lingam on the stem.

The occurrence of white stem rot, caused by the pathogen Sclerotinia sclerotiorum, was recorded only to a minor extent. At BBCH 85, maximum values of only 16 % (2004/2005) and 22 % (2005/2006) disease incidence (DI) could be documented in the untreated control. The quantity of apothecia formation proved to be only a very imprecise criterion for forecasting the subsequent level of infestation.

Verticillium longisporum could be detected at all sites on the basis of specific microsclerotia, but the infestation level differed markedly between the individual trial sites. Sites with a narrower, i.e. three-course, crop rotation showed the highest infestation values. No fungicidal control effects on Verticillium longisporum could be determined.

Growth-regulatory effects with regard to the shortening of the shoot axis length could be demonstrated in all treatments treated with fungicides in autumn. In both trial years, an autumn treatment led to higher overwintering rates.

The efficiency of fungicide measures with regard to pathogen control, plant-morphological effects and the pathogen tolerance of cultivars is discussed in the context of the host-parasite interaction.