The present study tries to answer the question, if hop- extract (Humulus lupulus) could be an effective fungicide against Plasmopara viticola. In the experiments, hop- extract on different extract concentrations was used on Zoospores of Plasmopara viticola and the reaction of these Zoospores was observed under the microscope. Afterwards, Plasmopara viticola- infected grape-leaf disks, young leafs and plants were treated with hop- extract. Additional to the laboratory work, a small survey was made. It was checked whether copper is really still such an important fungicide as it says in literature. It could be showed that the use of copper is still important in Austria and Germany, but not in South Africa. The hop- extract showed a good effect on Zoospores of Plasmopara viticola under the microscope. On leaf disks the effects were smaller; it seems the extract is absorbed by the leaf- tissue. A missing curative or translaminar effect of hop- extract affirms this theory. Aditionally, a systemic effect could be proved. It is remarkable that in all treatments the disease incidence, in contrast to the disease severity, was nearly not decreased by hop- extract. This leads to the assumption that hop- extract has a resistance- inducing effect through its phytotoxicity. Following the laboratory results, hop extract is not effective and trustworthy enough to be a replacement of copper in organic winegrowing. It could be used as an addition, but there would still be one more problem to solve: copper is complexing the hop- extract. It cannot be mixed without cementing the spraying- tools. One solution could be to isolate and concentrate the effective components of hop- extract. However, hop extract is a really interesting agent as an organic wine fungicide and should be further ascertained.