Organic plant protection product from microalgae against fungal infestation

Viticulture – in search of an alternative to copper

One of the major problems in modern winegrowing is the fungal infestation of vines. As a result of the harmful effect of fungi, such as downy mildew, not just the harvest but also the quality of the wine produced is severely impaired. Currently, to prevent fungal infestation, most organic winegrowers treat their vines with products that contain the heavy metal copper as an active substance. Copper accumulates in the soil and harms or kills, among others, valuable soil microorganisms.

Currently, the EU-Eco Regulation limits the use of copper to six kilograms per hectare and year and the German organic associations limit its use, on a voluntary basis, to three kilograms per hectare and year. However, the EU is pushing for copper fungicides to be replaced as quickly as possible. Unfortunately, at the moment there are no efficient alternatives to replace copper as a fungicide in organic or conventional viticulture. Therefore, an economical solution is required to support the development and growth of the organic viticulture market. The aim of the EU-funded ProEcoWine project was therefore to develop an environmentally compatible plant protection product made from microalgae which is suitable for organic winegrowing.

Cultivation of the microalgae

Microscopic image of the microalgae tested

At the University of West Hungary, a microalga strain with activity against downy mildew (Plasmopara viticola) was successfully selected from their algal culture collection and tested. At the Fraunhofer IGB, growth and biomass production of this microalga in the flat-panel airlift reactors (FPA) developed by the IGB was optimized. In the cultivation process, important parameters such as composition of the culture medium, concentration of CO₂ and mineral nutrients and, in particular, the light intensity on the reactor surface in relation to the cell concentration in the reactor, were determined experimentally. The optimized process was successfully transferred to the outdoor reactors of the Portuguese industrial partner A4F to produce the amount of algal biomass for the field trials in the vineyards.

Processing of the microalgae

© Fraunhofer IGB
Inhibition of the sporulation of grapevine downy mildew (Plasmopara viticola) after use of the protection product based on microalgae. Top: untreated leaf sections (control), bottom: treated leaf sections.

To release the fungicidal active substance, the microalgal biomass was disrupted by a mechanical treatment in a ball mill. In the process, it was possible to disrupt more than 95 percent of the cells. The subsequent conservation of the disrupted microalgal suspension was carried out by a thermal method, through air-drying at low temperatures. The dried product underwent several tests and showed a high fungicidal effect. No phytotoxicity effect was determined, meaning that the microalgal product is significantly more suitable for the plant than the existing copper preparations used at the moment.

Field trials

In order to test the effectiveness of the newly developed plant protection product, the project partners carried out appropriate field trials. Here, the product was applied to the vines using the customary spraying equipment in winegrowing. The results were very positive: the algae-based fungicide had success rates comparable to commercial preparations containing copper and the infection rates on the leaves were lower than with untreated vines.

Outlook

Based on these results the intention is, in collaboration with the SME partners, to design a pilot plant for manufacturing the algae-based fungicide for further field trials in different regions and under different climatic conditions. After completion of this test phase, the SME partners aim to commercialize the product in the European market.

Funding

The project “Development of a process to generate a novel plant protection product enriched with micronutrients to replace copper in organic viticulture – ProEcoWine” has received funding from the European Union’s Seventh Framework Programme for research, technological development and demonstration under grant agreement no 315546.