Powdery Mildew OR Bad White Zucchini

powdery mildew is a parasitic fungus that attacks various plants in the garden and orchard, often attacking cucurbits (pumpkin, zucchini, cucumber, etc.). In particular, this fungal disease is troublesome in pumpkin and squash plants, although it can be found in many other species, including perennials like fruit trees and aromatic plants like sage.

The fungus is also known as evil-white because it presents a whitening on the surface of the leaves, which makes it really characteristic and very easy to recognize.

The fight against powdery mildew in organic farming is possible , on the one hand with the aim of preventing it, on the other hand by the use of potassium, sodium or sulfur bicarbonate. Since this is one of the most common diseases in the garden, it is worth focusing on it, so let’s find out in detail how we can defend our zucchini against white disease.

Contents [Ocultar]

  • Features and Symptoms

  • How to Prevent White Evil

  • How to deal with diseased plants

  • Biological treatments against powdery mildew

    • Fight powdery mildew with horsetail

    • Vinegar

    • sodium and potassium bicarbonate

    • Sulphur: organic fungicide


Features and Symptoms

Mal bianco is a fungus that develops thanks to spores, called oidiospores, from microfilaments. It’s a ascomycetes of the family of Erysiphaceae . The damage it causes is mainly on the leaves.

As already mentioned recognizing the symptoms of powdery mildew is not at all difficult : especially in cucurbits such as zucchini and pumpkins, which have large leaves on which it stands out clearly and the white patina of the disease. After the first stage where you can see the white spots on the leaves, there will be yellowing and necrosis, until deterioration or total wrinkling. This damage obviously compromises photosynthesis, in general plants affected by powdery mildew have a growth retardation.


Like all fungal diseases too powdery mildew is spread by its spores , which can also be blown away. The preferred conditions for white evil to manifest are a moderate temperature (between 20 and 25 degrees) and obviously humidity. Therefore, pay special attention in the middle of the season, when treatment may be necessary.

How to prevent white disease

In organic farming, prevention must always be a priority: it is better to avoid the problem from the start than to use products which, although natural, can have minor consequences by altering the environment.

The first tip to prevent powdery mildew is to avoid planting our cucurbits too close together. Zucchini should have at least a meter distance between each plant, pumpkins even more. If the plants are well spaced, there will be good air circulation, preventing the increase of plant disease and if that happens in any case, preventing the spread of disease. To maintain aeration between plants, situations can also be thinned out with too coarse pruning of shoots and leaves.

Another essential precaution to avoid powdery mildew is to rotate crops, avoiding putting pumpkins or zucchini back in the same garden bed for at least 3 years. In general, for all diseases, the alternation of different types of plants is essential.

You should then avoid water at times when the temperature approaches the most favorable for the fungus (22 degrees), avoiding, if possible, wetting the leaf but spreading the water directly on the ground.

How to Treat Sick Plants

Powdery mildew is a fungus very resistant and difficult to eradicate . In organic farming, there are no products that can cure powdery mildew by curing the affected part of the plant, but the infection can be stopped. It is very important to constantly monitor the plants and to intervene quickly before the fungus spreads excessively and damages the whole crop.

Intervention against this disease is not simply a treatment. To stop the fungus in the first place all diseased parts of the plant must be removed (taking care to remove them and not to compost them and leave them on the ground) then carry out a treatment to protect the healthy parts. If the plant is very sick, you might as well eradicate it entirely.

When illness occurs, it is important intervene with treatments , obviously only using products authorized by organic farming. The aim of the treatments is to contain the disease, stopping its spread, so it is necessary to treat not only the plants that show symptoms of white disease, but the entire crop of species potentially prone to the problem.

can also decide on preventive treatments when the conditions are favorable to powdery mildew, the temperatures are therefore mild and very humid.

organic powdery mildew treatments

In organic farming, we have several possibilities to combat white disease in zucchini, pumpkins or other plants. Do not think that if a product is authorized in organic then it is exempt from effects on the environment: even a simple treatment with baking soda has little effect in ruining the structure of the soil and modifying the pH. So before intervening it is good to keep this in mind and also know the side effects, to dose the substance and not abuse it in the quantities or frequencies of the treatments.

The most effective organic remedies for the evil eye applicable to the garden are five , I list them in order of eco-sustainability, so it is better to start with the first, even if it is softer. Next, let’s take a closer look at the characteristics of each intervention.

  1. Equisetum decoction or maceration.

  2. Vinegar

  3. Potassium bicarbonate.

  4. Sodium bicarbonate.

  5. Sulfur.

Fight powdery mildew with horsetail

The equisetum is a spontaneous plant easy to recognize and widespread throughout Italy, due to its high silicon content can be used to strengthen plant defenses against fungal diseases. It is necessary to make a decoction or maceration, to obtain a liquid to be sprayed on our crops, these are really simple preparations and achievable in self-production.

Do not think of horsetail as a remedy, but as a support for prevention , treatments should therefore be carried out quite often in seasons favorable to white disease, before the problem arises. The beauty of this treatment is that it has no contraindications, so it does not pollute and can be used without precautions.

To learn more about the preparation and use of this natural remedy, you can read the article dedicated to the decoction of horsetail.


Vinegar is a very mild remedy for white disease, but its acidity is undesirable for the development of white disease spores. It is treated with water in which a little vinegar is diluted, the correct dose is one tablespoon per liter .

It is an artisanal method suitable for small orchards and also for balcony crops, since vinegar in general is always available at home. However, be careful not to overdo it. because a good amount of vinegar in the soil can kill plants.

sodium and potassium bicarbonate

Among the simple and inexpensive natural remedies, sodium bicarbonate and potassium bicarbonate can also be used, which have a similar action. It seems that hydrogen peroxide is also useful in combating the disease of zucchini plants.

The good thing about baking soda is that it is a cheap substance that is often already present in the household , as it is used for many purposes. One tablespoon of baking soda per liter of water is used for treatment. However, care must be taken that the use is moderate in frequency and quantity: the presence of baking soda in the soil is harmful to all plants, it also varies the pH, making it basic. If the small doses of baking soda sprinkled on the plants do not cause their overuse, they can create serious problems for the garden.

Potassium bicarbonate has an action very similar to that of sodium and is registered as an authorized phytopharmaceutical in organic farming your treatment only has one day off.

At Orto Da Coltivare you will find an in-depth study dedicated to sodium and potassium bicarbonate.

Sulphur: organic fungicide

The most important biological treatment against the white malolactic fermentation of zucchini is certainly sulphur. , considered the anti-environment par excellence, authorized in organic farming. The first thing to know if you want to use sulfur in the garden is to pay attention to its phytotoxicity. Indeed, at certain temperatures, sulfur becomes harmful to plants. In particular, sulfur treatment is ineffective if the temperature is below 15 degrees and harmful to the plant above 30 degrees, so care should be taken to do it in a timely manner.

Be careful then to remember that 7 days of shortage must be maintained between processing and harvesting. Sulfur is authorized in organic farming.

To spray this product with a pump sprayer, you need buy wettable sulfur (for example the one from Amazon has a good value for money). It is used in doses of approximately 20 grams per 10 liters.

You can also simply use sulfur powder, without dilution. It is better to spread it on the plants using a sulphur, there are electric or manual models, you can always find this manual on Amazon, which is quite cheap.

It is better to repeat the treatment after two weeks, even if a very good result is already found after the first stage, so that the disease is definitely eradicated.

For those who want to choose this remedy, you can read more in Sara Petrucci’s article on sulfur. .

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