Powdery mildew: how to fight and treat your plants?

Powdery mildew is among the plant diseases that bother all those directly or indirectly linked to culture. At the beginning of damage considerable that it causes on plants of all kinds, this white rot sometimes named white disease must be treated as soon as possible. It is also possible to prevent it with a few relatively simple solutions to apply. Let’s take stock of powdery mildew, a fungal disease to be taken seriously and the best means to take into consideration to save your plantations.

Powdery mildew: a fungal disease

Powdery mildew is a term for different fungal or fungal diseases since the culprits are fungi. They target many plants. The phytopathogenic fungi responsible for this disease also called white rot are part of the division Ascomycetes (Ascomycota) whose shapes are extremely varied, belonging to the family of Erisiphaceae and genres Sphaerotheca, Uncinula, Erysiphe and Podosphera.

Powdery mildew parasitizes countless plants, from tomatoes to maple trees, from vines to ornamental plants, including clover, citrus fruits, crucifers … This “white disease” is a real plague for agriculture as for the vegetable garden, the fruit tree and the ornamental garden.

White rot or powdery mildew: conditions most favorable to the disease

To develop, powdery mildew needs special conditions. The proliferation of phytopathogenic fungi is greatly favored by a hygrometry (humidity level) high around 75% despite a dry weather. These are conditions that are found more specifically during the second part of spring, when the heat begins to set in but the humidity is still quite substantial and that in addition, there are temperature differences relatively important between night and day periods.

The disease that settles among others in the buds resists perfectly in these organs throughout the winter. When the young shoots start to re-start, they are then fully infected with powdery mildew. They are given the very specific name of “flag shoots”.

Powdery mildew: signs to look out for

Whatever plants are affected by a powdery mildew attack, they show the following signs:

  • A greyish white powder which looks like flour and forms a kind of felting on the aerial parts of plants, i.e .:
    • The stems,
    • Sheets,
    • The buds,
    • Flowers,
    • The fruits.
  • A leaf deformation of the host plant, such as blistering, curling, curling up. Note that in some plants it is first of all the young leaves that are affected, while in others, powdery mildew deforms the old leaves, which more specifically threatens late harvests.

This fungal disease, in addition to causing the dry leaves then their fall, can drastically reduce yield in the absence of treatment or cause severe aesthetic damage on ornamental plants.

Powdery mildew or white rot: solutions to treat plants

Let’s review the different means of combating powdery mildew, their advantages and disadvantages.

The ladybug at 22 points

Psyllobora vigintiduopunctata is a small beetle from the family of Coccinellidae. It is a 22-point ladybug that has the particularity of feeding exclusively on ascomycete fungi responsible for powdery mildew disease.

Its usefulness can however be questionable insofar as the ladybird can contaminate other plants by moving from plants affected by powdery mildew to healthy plants. There is therefore an interest in using this beetle only if all the plants in the garden are affected by white rot …

Potassium bicarbonate

This is a non-toxic product, economical and biodegradable which gives good results in the fight against fungal diseases. He neutralizes the acidity of the environment in which phytopathogenic fungi proliferate. Thanks to its antifungal action, potassium bicarbonate therefore eliminates powdery mildew.

On the other hand, we can blame it for taking on moisture in just a few hours so that it solidifies and becomes very difficult to use.

Sodium bicarbonate

Made from natural minerals, the one commonly (and incorrectly) called baking soda, is actually thesodium hydrogencarbonate. It is among the most widely used treatment products to effectively eradicate powdery mildew. In addition to being very inexpensive to purchase and easy to use, it is non polluting. It is the perfect ally for the gardener because it can be used in orchards and vegetable gardens as well as on ornamental plants.

A sulfur product

Of sprays are necessary to stop the development of white rot but they should not be carried out when the sunshine is important because this causes burns on the leaf system.

Sulfur is a plant protection product which can be applied as a powder on plants or after dilution, strictly compliance with the recommended dosages by the manufacturer. A registered sulfur product must be purchased for use as a fungicide on infested parts of vegetable crops, fruit trees, ornamental trees, and flowering or ornamental foliage plants.


Diluted at 10% in water, the whey should be sprayed regularly on the leaves when the light is strong. It is therefore preferable to treat in bright sunlight because the light causes a particular phenomenon: peroxide radicals are formed under its action in the milk serum. Powdery mildew does not resist it because these radicals have a high toxicity for this powdery mildew disease. Note that we can use skimmed milk instead of whey.

Milk treatment against powdery mildew requires that this dilution be observed at 10%. It should be known that other families of pathogenic fungi can develop in the event of an overdose.


If we have few plants to treat, it is possible to prepare a homemade treatment product, namely an infusion of garlic because of its sulfur compounds. We add a bit of milk for its antifungal properties but above all because it acts as an adhesion adjuvant, in other words a kind of natural fixative.

Horsetail decoction

Horsetail, nicknamed ponytail is mistakenly considered a “weed”. On the contrary, it is a very useful wild plant against powdery mildew. It is enough to cut its stems then to dry them in the sun. 100 g of dry horsetail are then macerated in 2 liters of water for 3 hours. This mixture should then be boiled for 20 minutes. Once cold, all you have to do is filter it before using it by spraying it after having diluted it at the rate ofone volume of horsetail decoction for four volumes of water.

It is recommended to renew the treatment regularly. It is better to prepare a decoction just before each use because this mixture does not keep very long.


Certainly hyper effective even in the event of a strong powdery mildew infestation, bleach presents a major drawback : it radically destroys the flora and fauna that live in the earth. However, these are absolutely essential to ensure soil fertility. We therefore keep the hand ultra light with this type of treatment, and as far as possible, it is better to give preference to other solutions.

Powdery mildew (powdery mildew): means of prevention

Some actions can be taken as a preventive measure. We can for example:

  • Observe sufficient space between the plants when planting so that the humidity is moderate,
  • Apply with regularity preventive solutions on all plants known for their sensitivity to powdery mildew,
  • Water at the foot and take care not to wet either the leaves or the flowers,
  • Allow air to circulate in the heart of the plantations by carrying out a regular weeding around its cultures.

It is recommended to always take precautions when we must treat your plants, whatever the product used, which includes natural treatments. Gloves, a mask but also protective glasses must be worn in order to limit the risk of burns by contact but also to avoid inhaling these products which can prove to be irritating. Particularly beware of sulfur vapors.

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