Strategies for copper reduction in grapevine, apple, roses and vegetables by using alternative experimental products

Summary

Reducing the use of copper fungicides with the aim of phasing out has a high priority in European policy as well as in organic farming. To reach this goal without compromising yields, all preventive strategies have to be implemented and several affordable alternative products need to be brought to the market. Within the EU-funded project RELACS (2018-2022), we investigated alternative compounds that had reached a high technology readiness level. We focused on major copper-relevant crops/pathogens (grapevine/Plasmopara viticola, apple/Venturia inaequalis, vegetables/downy mildews/late blight, oil-producing roses). As alternatives, two plant extracts including licorice leaf extract (Glycyrrhiza glabra) and a larch bark extract (Larix decidua), a rare sugar (tagatose) as well as a test product based on fatty acids (NEU 1143F in apple) were evaluated. Refined strategies with these alternatives were tested, adapted and validated under practical conditions in different European countries, and further aspects of importance (e.g. mode of action, wine fermentation, compatibility with other plant protection products) examined. All alternatives proved to be effective in one or more of the investigated crops. In some cases, their efficacy as stand-alone treatment was comparable to that of copper. In other cases, the combination of the alternatives with reduced amounts of copper or in combination with other standard methods provided effective protection of the crops.