Exploring Novel Plant Defence Stimulators for Reducing Downy Mildew (Plasmopara viticola) in Grapevines in Brazil

In older vineyards, copper concentrations from prolonged use of copper-based fungicides can build up in the soil, harming soil life, plants, and sometimes local aquatic life due to run-off. Copper levels of up to 496 mg/kg of soil have been found in vineyards in Europe and over 1,800 mg/kg in vineyards in Brazil, whereas the level that adversely affects earthworms has been demonstrated to be 45 mg Cu/kg of soil. In 2019, European law changed to dramatically reduce the allowed amount of copper used in viticulture to 4 kg/Ha, averaged over 7 years, and so it is important to find an alternative strategy for the control of downy mildew, which can otherwise devastate a grape crop. This is particularly important for organic viticulture, which currently has no alternatives. This research aims to evaluate the effect of different homeopathic and biodynamic preparations on the resistance of grapevines to downy mildew by measuring the levels of protein and some protective enzymes in the vine leaves before and after treatment. Twelve homeopathic and biodynamic preparations were first screened for their effectiveness in increasing leaf protein levels of Isabel vines. The best of these were used in a larger-scale experiment using 80 Pinot Noir and 80 Chardonnay vines. All the treatments were double-blinded, and distilled water controls were used. The leaves were collected at four harvest times, and then extracts were made and the protein and protective enzyme concentrations measured using spectrometry. Early results indicate that some homeopathic and biodynamic preparations elicit an increase in protein and some protective enzyme levels, indicating possible increased plant protection against downy mildew. Severity and incidence experiments are now needed, and if the vines are found to be more resistant to downy mildew, then field trials will follow.