Powdery mildew or white sickness is a cryptogamic disease, that is of fungal origin, which can affect sage plants and occurs on the leaves. This is the most frequent pathology among those that can affect this aromatic herb and occurs in particular with mild temperatures and high humidity.
It is a very simple disease to identify: because the white patches that are seen on the leaves of the sage are very characteristic. A reader of our website, Barbara, asks me exactly what her plant can have, describing the symptoms of powdery mildew. I answer publicly because I think it may be useful for many to know how to defend themselves from this problem with natural methods and above all how to prevent it.
Recognizing powdery mildew on sage
Those who cultivate the vegetable garden will already know powdery mildew because it is a frequent pathology also on other cultivated plants, in particular on pumpkin and courgette. Powdery mildew is also called white sickness precisely because it works by blotting the leaves of affected plants with white. This is a patina that is mainly visible on the upper part of the sage leaves. This aromatic is characterized by a rough leaf surface, covered by light down that sometimes retains some moisture and favors the lingering of the spores of this pathogen.
The white malady is recognizable at first sight and is easy to identify. This disease is quite slow in progress but after the white patina, it leads the leaves to dry out and can get to completely compromise the sage. To be able to save the plants it is very important to intervene promptly to fight the disease.
Powdery mildew occurs when there is a lot of humidity and temperatures are mild (between 15 and 25 degrees), typically this climate occurs in spring and autumn, periods in which the leaves must be monitored periodically, to notice the white sore at the first symptoms.
How to combat powdery mildew
Let’s start with the bad news: powdery mildew cannot be cured and the affected parts of the plant are doomed. The first thing to do if we find the white spots of this pathology is to remove all the affected leaves by pruning the shrub. After removing the diseased parts, let’s eliminate them by burning them, and we must also disinfect the scissors used to cut them off. Do not underestimate these precautions, otherwise, the infection will spread to other plants.
Once this is done, it is good to intervene on the parts of the plant where the spores have not yet manifested their presence, in organic farming we can do it with two treatments.
- Sodium bicarbonate. Very low cost remedy, which allows the leaves to be used immediately after treatments. The only constraint is that it should not be used too frequently because its accumulation in the ground creates problems in the long run, including the variation in PH.
- Sulfur. It is probably the most effective treatment against powdery mildew available in organic farming, but it has its own toxicity and a shortage period. So the advice is to use sulfur only if strictly necessary and then take into account that you will not be able to eat sage for a few days. On the product label you will find information about risks, precautions and exact waiting times.
I have also heard about the use of vinegar and hydrogen peroxide to counteract powdery mildew, frankly, I have never experienced these “grandmother’s remedies”, feeling good with baking soda, I just report these possibilities. If anyone has any experiences with it they can share them in the comments.
How to prevent the disease
If you have a healthy sage plant, it is important to know that it can be subject to powdery mildew, to implement the right cultivation practices to avoid this problem.
Like all spores, powdery mildew is favored by humidity, stagnant water, and little air circulation. Important preventive measures are, therefore:
- Ensure a well-drained soil, without water stagnation. In the garden it is carried out with a deep tillage of the soil (digging), possibly raising the cultivated plot (trunks). If the sage is grown in pots, on the other hand, a layer of gravel or expanded clay must be placed on the bottom of the pot.
- Take care of irrigations. Sage requires little water when grown in the field, and is sensitive to excesses even in pots. Never irrigate excessively and if possible it is better to wet the soil, not letting water linger on the leaves.
- Strengthen the natural defenses of the plant. There is a natural treatment that can be self-produced in a simple way and that helps strengthen the immune defenses of plants: horsetail decoction. I list this remedy among the preventive and non-curative methods, since its action is mild and less suitable for dealing with an ongoing pathology than bicarbonate or sulfur.
- Promote the circulation of air. For the air to circulate well between the sage bushes, it is good to keep the right distance between the plants, so avoid planting the crops too close. In addition, regular pruning of sage also favors the prevention of powdery mildew.
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