Sowing sugar beets with a John Deere tractor

Powdery mildew

Powdery mildew

Powdery mildew is a fungal disease. The pathogen is the fungus Erysiphe betae. The fungus is observed in all sugar beet growing regions around the world. It is of particular importance in areas with dry and warm climates.

At the beginning Powdery mildew is hard to detect. When the leaves are shimmering white-gray, the infestation is already advanced.
At the beginning of the infection a fine white structure appears on the leaves. As the infection progresses, the leaves become covered in what looks like flour. The mycelium can be washed off.
If the mildew infestation is severe and persistent, the mycelium turns gray and the leaf below begins to dry up.
Powdery mildew is spread in dry and warm summer. The yield losses can be as high as for Cercospora.
The early visible infestation with leaf diseases represents "the tip of an iceberg".

Powdery mildew, Erysiphe betae, forms a mycelium only on the leaf surface with gray-white conidia. Hyphae penetrate the epidermal cells and attach the mycelium on the leaf with the help of haustoria. The fungus supplies itself with nutrients from the haustoria. (Diagram) The mycelium is initially perceived as a spider web- like structure on the leaf surface resulting in a powder-like covering which is looking like flour. The white gray covering can be washed off. The conidia of the fungus are spread by wind. 

In contrast to Cercospora, powdery mildew does not lead to the death of cells and tissue. Loss of yield is caused by its parasitic way of life.

And then again in comparison to Cercospora, the occurrence and spread of powdery mildew is favoured by warm, but dry weather. Powdery mildew infestation can cause yield losses that are as high as those with Cercospora leaf spots. An early infestation in July must be treated according to the threshold of infection. The plants should be checked by the end of August.