Downy mildew outwitted milk in 2021

n 2021, a year when pressure from downy mildew was high, treating vines with skimmed milk limited the damage, but only copper seems to have been really effective in combatting the fungus. “My vines experienced 550 mm of rainfall between May and July”, recalls Jean-Denis Perrochet, from Domaine de la Maison Carrée in the Swiss part of Jura, vividly.

The spread of mildew spots from July onwards forced him to spray Bordeaux mixture on the 2.8 hectares of Chasselas, Savagnin and Pinot vines that he had planned to protect using only skimmed milk collected the day before from a neighbouring farmer, based on convincing results in 2019 and 2020.

“I saved myself 7 copper sprays, but I should have used it a little earlier because this time I am a long way off achieving potential yields everywhere, especially for the Chasselas and the areas with least ventilation”, he regrets.

Concurrently with this, in a bid to better evaluate the effectiveness of the milk, Perrochet worked with a backpack sprayer over 2,000m², keeping untreated control blocks and protecting some rows with milk and others with copper. At the end of the season, David Marchand, a technician from the research institute for organic agriculture (FiBL), compared the two techniques.

Of the 4 untreated control blocks, he found nothing to harvest. The milk saved at least 60% of the fruit, and the copper 100% of the crop. “David Marchand monitored other trials and told me that milk is the only alternative to copper that was effective this year, even partially”, comments Perrochet.