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An expert explains the mistake that farmers repeatedly make when combating late blight in potatoes.
Krautfäule is one of the most significant potato diseases. An expert explains a persistent myth among farmers about plant protection that does not contribute to combating the disease.
In practice, the persistent myth remains that high amounts of water are needed for fungicide measures for potatoes (especially during stop spraying). However, this is particularly counterproductive when using systemically acting fungicides. Read also: Cicadas in Bavaria and Hesse: In these districts, farmers are allowed to spray.
Fighting late blight: The right amount of effort is essential
Why high amounts of water are not helpful can be explained professionally: systemic active substances have very high water solubility, so they spread very quickly in the plant. Fat solubility, on the other hand, is very low. Therefore, it is difficult to get the active substance through the "fatty" wax layer of the potato.
What farmers must pay attention to when combating late blight
It is crucial, therefore, to concentrate the plant protection product on the leaf surface. The more active substance, or the less water in the spray solution, the higher the concentration of the active substance in the spray solution. Therefore, for stop spraying with systemic products, the water volume must be limited to 200 l/ha. If the product permits, spraying can also be done with 150 l/ha. However, attention must be paid to an adapted spray pressure and thus a suitable droplet spectrum. If small amounts of water are applied with coarse droplets, the effectiveness decreases.
This is how more active substance reaches the potato plant
Another way to increase the uptake of the active substance Cymoxanil is to lower the pH value in the spray solution. This shifts the ratio of fat/water solubility, and the active substance is effectively absorbed by the plant even at lower humidity. In addition, the active substance molecules of Cymoxanil lose their charge through the pH value reduction and can, therefore, be absorbed more quickly by the plant.
