Gardening: Control powdery mildew on roses and other plants

Powdery mildew can become a real nuisance for the hobby gardener. Roses in particular are susceptible to fungal attack. The Stiftung Warentest reveals in its crop protection guide how to recognize powdery mildew and which tips can help against powdery mildew. Milk has proven to be an effective home remedy.

  • Is the infestation strong or weak?
  • What is powdery mildew?
  • How do you recognize powdery mildew?
  • How do strawberries and grapes react?
  • How do you recognize downy mildew?
  • Which home remedy helps?
  • How do you fight powdery mildew properly?
  • How do you prevent the fungus?

Especially when it is dry and warm for a long time, white spots form on the leaves of many plants in the garden. Powdery mildew is a fungus that, for example, grows on the spindle bush, Rosen, Cherry laurel, hydrangea, Rock pear and Trumpetenbaum occurs.

Is the infestation strong or weak?

But the infestation is not always strong enough to cause serious damage to the plants. Rather, the plant protection service of the North Rhine-Westphalia Chamber of Agriculture considers control to be “often not necessary”.

A rose with rose rust (Source: Getty Images / fotokate)

Hobby gardeners recognize a very strong infestation by the fact that the leaves subsequently also turn brown and die. Otherwise there are only individual white, floury-like spots on the green, which increase in number and size until the leaves are completely covered with them.

But of course it doesn’t look nice. If you are bothered by the fungal attack, you should remove the affected leaves and dispose of them in the residual waste.

What is powdery mildew?

When it comes to powdery mildew, a distinction is made between “downy mildew” and “powdery mildew”. Both variants spread via spores. They form a network of very fine fibers, which is also called mycelium. It is noticeable on the plants as white to gray fur.

Powdery mildew thrives particularly well in a moist environment. Both species form different species that cannot be transferred directly from one plant genus to the other. Apple powdery mildew for example, cannot skip on roses.

How do you recognize powdery mildew?

Powdery mildew forms a white, flour-like coating on the upper side of the leaves, where it can easily be wiped off at the beginning of the infestation. In the advanced stage, the shoot tips, buds and fruits as well as the underside of the leaves are usually also affected. In the course of the disease, the leaves roll up and some of the shoots cripple so badly that no further growth is possible.

The fungus spreads rapidly, especially in dry and warm weather in combination with nocturnal dew. Sunny days in spring and autumn as well as late summer therefore favor the spread of powdery mildew. In late autumn the fungus then forms dark winter fruit bodies that can overwinter in fallen leaves and other plant remains.

How do strawberries and grapes react?

There is an exception in the appearance of powdery mildew, for example, when infesting strawberry plants or Grapevines. The leaves of the strawberry turn red on the undersides of the leaves and hardly form a white coating on the upper sides. The leaves curl upwards. The leaves of the vines also change color similarly and the grapes burst open as the disease progresses.

How do you recognize downy mildew?

Many vegetables and herbaceous plants are attacked by downy mildew. When the plants are infested, you can tell by the reddish-purple spots on the upper side of the leaves. Many species also show yellow to brown spots that are bordered by the leaf veins. On the other hand, a dirty gray fungus lawn forms on the underside of the leaf. Buds and shoots often dry out, with grapevines even the fruit dry up.

The growth of downy mildew is favored by damp and moderately warm to cool weather, as well as by excessive nitrogen content in the soil. The fungus is constantly developing new subspecies, against which new resistant plants are being bred again and again. When buying such plants, one therefore often discovers information such as “against race 1–26” on their declaration.

Which home remedy helps?

Milk has proven to be a simple home remedy for powdery mildew: Mix one part of milk with nine parts of water and spray the mixture on the infected plant. It is important that it is fresh milk. The microorganisms in the milk fight the fungus. Therefore, long-life milk is unsuitable for this purpose. The lecithin in milk fights the fungus and the sodium phosphate strengthens the plant’s defenses. You should repeat the procedure two to three times a week.

How do you fight powdery mildew properly?

In general, all plant residues and infected parts must be removed and disposed of in the residual waste, as the fungus can overwinter in them. It also survives on garden tools, wooden posts or privacy fences made of organic material. It is therefore particularly important to thoroughly clean equipment and planters after coming into contact with diseased plants. Use an antiseptic or alcohol for cleaning. Incidentally, this also applies to your hands.

When using pesticides, one must always proceed with caution. Only infected plants may be wetted with the toxins so as not to damage beneficial organisms and healthy neighboring plants. When treating fruit and vegetable plants, you should always observe the waiting times indicated on the fungicides for your own protection. They refer to the minimum period after which the fruits and vegetables can be safely consumed again.

How do you prevent the fungus?

Fungal diseases such as powdery mildew are best kept away by taking preventive measures. It is always difficult to stop the disease after an infestation. In addition, the most necessary cuts on bushes and trees look ugly. If you … this Control and care tips against powdery mildew Note, your plants will stay strong and healthy in the garden and on the balcony.