Last updated on October 23rd, 2023 at 08:19 pm
What is powdery mildew?
Powdery mildew is a disease caused by a parasitic fungus, that is to say; it settles in the plant to benefit from its mechanism and in turn produces a disease.
With fungi, the problem we have is that most of them are microscopic, so the identification of the disease they can do in a plant is done when we observe the symptoms.
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What does powdery mildew look like?
Description and symptoms: most of the time it develops on the upper side of the leaves, although it can also spread to the stem or fruits if the attack is not controlled. It appears as white spots that turn into a white or gray powder that coats the leaves and, when removed, leaves yellowish spots. They hinder photosynthesis and if the attack is not controlled, the leaves may turn yellow and become deformed or dry. It is probably the easiest fungus to detect, because of its characteristic white powder.
Because of this shape and color, it is common to refer to powdery mildew as ashy or white disease.
If the disease is already advanced, you will see small balls containing the spores.
Affected crops: powdery mildew on cucumber, powdery mildew on pumpkin…
Powdery mildew is a fairly common disease in cucurbits, such as pumpkin (Cucurbita maxima duchesne), zucchini (Cucurbita pepo), melon (Cucumis melo) or cucumber (Cucumis sativus). As you can see in the photos and unfortunately you have already seen it in some of your orchards, powdery mildew has that characteristic way of identification.
It can also affect other vegetables, such as beans (Phaseolus vulgaris), chard (Beta vulgaris), spinach (Spinacea oleracea) or potatoes (Solanum tuberosum).
But undoubtedly, the best known powdery mildew is grapevine powdery mildew.
It is a disease caused by the fungus Uncinula necator. It spreads through all green parts of the plant:
- White powder appears on the leaves.
- In the bunches, the grain is covered by the powder, giving a rotten appearance and affecting the quality of the grain.
Why does it appear in our orchard?
Powdery mildew usually appears in areas with high humidity and temperatures between 10ºC and 20ºC. So BE CAREFUL with the irrigation that we give to our crop.
With this combination of temperature and precipitation, it is not surprising that powdery mildew can appear in spring or late summer; when temperatures are calm and rain is common.
We also have to be careful when we are going to use our tools (hoes, blades…) because if we cause any cut or wound, with the humidity; these areas can be affected.
So we see again that the planning of our orchard can be the first step to combat any disease. Very shaded areas, poor ventilation, bad pruning or excessive irrigation can be agents that benefit the appearance of powdery mildew in the orchard.
Another cause is the excess of nitrogen, also due to excessive fertilization, as this forces the plant to absorb more water than normal.
Powdery mildew: How to eliminate it?
Prevent the appearance of powdery mildew
The first thing to do is to remove the areas affected by powdery mildew. This will prevent it from spreading to other parts of the plant.
So a good pruning and a proper aeration of the soil, can be two activities that help us to prevent it from appearing. I also recommend that you take into account what you are going to put in your garden. Maybe your garden is not suitable for chard because of its humidity and it is better to move it or put another plant that is better adapted to your garden.
The main element that we have to keep in mind to eliminate this problem is the sulfur that can be applied directly in powder form on the plant or in liquid solution.
Preparations to control
As for control preparations, I am going to list some that may be interesting:
- Horsetail; it works as a preventive and you can prepare it at home by putting about 20 grams of dry plant per liter of water with 5-10 grams of soda silicate for a day. Then boil it for 20 minutes and strain it. The dissolution of one part of the preparation in 9 parts of water is sprayed.
- Garlic; is another preventive that you can prepare at home by preparing an infusion with 50 grams of garlic cloves per liter of water and pulverizing the solution of one part of infusion in 4 parts of water. It should be applied in full sun and for several consecutive days.