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Soybean downy mildew

Peronospora manshurica

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Downy mildew of soybean is caused by the pathogen Peronospora manshurica. Downy mildew fungi (Peronosporaceae) belong to the class of egg fungi, which are also known as oomycetes. Drippable water, such as dew, is essential for the life cycle of egg fungi.

Damage symptoms

On the upper sides of the leaves, small, light to light yellow spots can be seen at first, which are between 2 and 8 mm in size. The spots enlarge, are irregular in shape and size, and eventually merge. The infested leaves wilt and die. On the undersides of the leaves, a grayish-purple sporangia can be seen on the dead tissue.

Pods can also be infested, but no symptoms can be seen on them externally. On seeds within pods, downy mildew develops on the seed surface and forms a milky white crust consisting of the surviving spores (oospores). Plants that grow from infected seeds remain small, are stunted, and soon die.

Host plants

The host plant is exclusively the soybean.

Distribution

Peronospora manshurica is distributed worldwide.

Propagation and transmission

The pathogen is usually transmitted with the seed, but can also survive on infected plant residues in the soil in the form of permanent spores. In the stand, downy mildew is spread by sporangia spread by wind and water droplets.

High humidity and cooler temperatures promote disease development.

Economic importance

Depending on the soybean variety, yield losses can be as high as 20%.

Prevention and control

  • Adherence to a crop rotation of at least three years
  • Use of healthy seeds
  • Deep bagging of crop residues

Last updated: 23.11.2021

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