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Downy Mildew

English name (engl. downy mildew) for downy mildew; see there.

Term for two dangerous plant diseases caused by fungi. They were unknown in Europe until the second half of the 19th century and were first introduced from North America with contaminated vine material. Shortly afterwards, phylloxera and another plant disease, black rot, were also introduced from North America, which is why these pests were referred to as the "four great plagues".

The two mildews feed on the living cells of the infested host, which is why they are categorised as biotrophic parasites. There are plant-specific ones for apples, peas, cucumbers, roses, spinach and grapevines. The strictly host-specific fungi can only live on their host or hosts. Although the different disease symptoms are clear, the two fungi are often confused due to their similar names.

Control

The two fungi grow in different weather conditions. Accordingly, powdery mildew is referred to as a "fair weather fungus" and downy mildew as a "bad weather fungus". Nevertheless, there are some similarities in terms of prevention. The plants should not be planted too densely so that the leaves can dry out quickly (dew could also favour the growth of powdery mildew). A sunny location is preferable because sunlight boosts the vitality of the plants and at the same time inhibits growth.

Conventional control is carried out using sulphur (powdery mildew) and copper sulphate or Bordeaux broth (downy mildew). In addition, special fungicides or plant strengthening agents are used. This is often necessary several times during the growing season. For environmentally friendly reasons, the use of newly bred fungus-resistant PIWI varieties with high resistance is increasing today. Some species of ladybird feed exclusively on mildew. However, this has no significance in terms of control.

Early warning systems

Rose bushes are often planted at the edge of vineyards or at the end of each row of vines as an early warning system. They act as "sentinels" or indicator plants because they are attacked by both types of mildew earlier than the vines and thus inform the winegrower of the infestation in good time for the purpose of preventive defence measures. They also provide shelter for beneficial insects. This is common in the French wine-growing region of Graves.

Powdery mildew (Oidium)

The pathogen that causes the disease belongs to the tube fungi (Ascomycota), the botanical name is "Erysiphe necator...

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