Downy mildew on poppy

Peronospora arborescens


Downy mildew on winter poppy is caused by the pathogen Peronospora arborescens. 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

The first symptoms of downy mildew are yellowish brightenings on the tops of the leaves, sometimes the entire plant is discolored yellow. These spots are between 0.5 and 4 cm in size. The infected tissues are often curled, bulging or thickened. Infected young plants are conspicuous in stands by their pale or already yellowish-white leaves. They are retarded in growth and may also die completely. Infested flower stalks turn inwards, the buds or sepals can also be infested and the plants subsequently die. If the capsules are infested, the seeds are also infected. The typical, initially whitish, later grayish-purple sporangia can be seen on all infested plant parts, especially in humid weather.

Host plants

In addition to Papaver somniferum, Papaver alpinum, P. dubium, P. caucasicum, P. nudicaule, P. rhoeas, P. setigerum, and Mecomopsis spp. are also infested.


Peronospora arborescens is widely distributed in Algeria, Egypt, Afghanistan, Azerbaijan, India, Iraq, Japan, Turkey, Pakistan, Australia, Argentina, and Europe.

Propagation and transmission

Spread occurs through infected seeds. Furthermore, the pathogen forms sporangia carriers with sporangia, which release mobile spores (zoospores). The sporangia usually grow on the undersides of the leaves from the stomata or other openings in the plant. The sporangia are spread by wind or rain. The zoospores require dripping water to travel and germinate. After germination, they penetrate directly into the plant tissue.

To survive, the pathogen forms robust spores (oospores). They are spherical and dark brown in color, but not visible to the naked eye. Oospores can survive in the soil for several months.

Economic importance

In damp and cool weather, downy mildew is likely to occur on winter poppies. Between 10 and 20 % of the young plants can be infested. Reduced yields are the result.

Prevention and control

Last updated: 23.11.2021

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