Einfluß von sortenspezifischen Merkmalen, unterschiedlichem Stickstoffangebot und Kupfer auf die Ertragswirksamkeit von Phytophthora infestans in Kartoffeln

Summary

Three potato varieties – Nicola, Rosella, and Simone, differing in the time of initiation of tuber formation (early, middle, late, respectively) – were grown in a 3-factorial field trial for two years in 2 rotational positions i. e. after grass clover and winter wheat in order to induce a different fertility status. A copper control was included. Nitrogen supply after grass clover was between 26 to 32 kg higher than after winter wheat. Late blight severity was high in 2002 but almost nil in 2003 (Area under the curve 1100 versus 75, respectively). In both years, it was consistently but not significantly higher after grass clover. N-mineralisation rates in 2002 were below average due to unfavourable weather conditions in May and June. Thus, only in 2003 the additional N-supply after grass-clover was translated into significant yield increases. Although Simone was most resistant it did not yield more then Nicola while Rosella significantly outyielded the other two varieties in both years. While copper treatment had a moderate but significant impact on disease severity in both years, yield increases due to copper were only 1 and 5% in 2002 and 2003, respectively. It is concluded that the combination of the fertility status of the site and varietal choice is an important system based means of reducing yield losses due to late blight in organic potato production while the use of copper fungicides may not result in the desired yield effects.