Vine diseases don’t care if you treat your vineyard in conventional, integrated or organic way. The only thing you can be sure about is that you will have them, no matter what. While conventional growers fight diseases with synthetic fungicides, organic growers have to search for more nature-friendly solutions.

Powdery mildew is probably one of the most serious grapevine fungal disease worldwide. It is present in almost every vineyard and represents the biggest challenge for organic wine producers to fight with. To determine the timeframe in which the disease is most susceptible, the organic wine growers are using disease predictive models. Which actions can organic wine grower take in order to successfully manage powdery mildew?

(Micro) climate
Humidity, air drainage, and wind exposure are influencing vineyard humidity and the drying rate of vine foliage. In general regions with hot, dry, sunny climate are less favorable for powdery mildew.

Row orientation & Canopy structure
The goal is to create an environment less favorable for powdery mildew and other diseases, which means a reduction of the humidity level as much as possible. We can achieve that by adjusting canopy structure, it should be opened and designed to maximize exposure of the foliage to sunlight and to maximize air movement. We can increase air movement in the rows if we face the end of the rows into the prevailing wind. If the canopy is properly managed, we can also reduce levels of shading and improve spray application efficiency and distribution throughout the canopy.

Flag shoot removal
Cleistothecia that overwintered on the grapevine is the primary source for powdery mildew. First infections come from flag shoots and removing them can significantly decrease the number of necessary spraying. This early season task minimizes early spore production and so reduces the impact of powdery mildew.

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Flag shoot removal - powdery mildew. Organic wine growing.

Image Copyright: Pacific Northwest Plant Disease Management Handbook: Grape (Vitis spp.)-Powdery Mildew

• Sulphur is probably the most used sprays against Powdery mildew in organic wine growing. It does not kill the fungus itself. It is used to prevent the vines from being infected.
• Potassium bicarbonate disrupts the cell walls, causing the fungi hyphae and spores to collapse. Usually, it is applied with canola oil for powdery mildew control. PB does not protect the vine against new infections and requires more frequent application than sulfur.
• Other alternative fungicides such as various oils, dilute hydrogen peroxide, sodium salt and diluted milk can be as effective as sulfur, but they are often suggested for use under certain conditions such as low to moderate disease pressure.

Fighting Powderly mildew in an organic way is no longer fairytale for naive »eco trend« buyers. It is real and organic wine growers are practicing it. Good vineyard management software with the disease prediction system and regular monitoring of the vineyard are key factors winegrower needs to pay attention to in order to win the fight with Powdery mildew and other vine diseases, and to produce the wines of excellent quality.

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