Copper based active ingredients are essential for disease control in organic farming. However, copper accumulates in the soil and can lead to toxicity that negatively affects microbial biomass and activity. The aim of this study was to test the efficacy of a phosphite based product against downy mildew.
Foliar fertilizers based on potassium phosphate and magnesium phosphate has been proven to provide some protection against downy mildew. Phosphites stimulate the production of phytoalexins – metabolites produced by plants that assist with systemic induced resistance and that break cell membranes of pathogens
The trial was done in a 15-year old dryland Barbera vineyard in Italy. Four treatments were applied:
- Control: Untreated vines – no disease control agent applied.
- Cu: Traditional copper based product (20% Cu) used against downy mildew. Total of 4.5kg/ha Cu.
- CuS: Traditional copper based product plus Scudo – a liquid fertilizer consisting of copper chelated by gluconic and amino acids. Total of 3.4kg/ha Cu.
- PhoS: Phosphite based fertilizer plus Scudo. Total of 1.8kg/ha Cu.
Seasonal weather was also monitored.
The PhoS treatment showed a good level of protection, similar to the traditional Cu treatment and reduced the copper dosage by 40%.
- The CuS treatment provided the best protection and reduced the copper dosage by 22%.
- Levels of phophonates and copper in the harvested grapes were well below the legal limit.
- Grapes from the PhoS treatment showed the highest anthocyanin and phenolics content.
SIGNIFICANCE OF THE STUDY:
The results from the study showed promising alternatives that allow for reduced copper use in order to protect vines against downy mildew in organic farming.