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Mildew – and how to preserve it.

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What is mildew?

When you ask yourself a question like this, the best thing is often to ask Wikipedia :

Mildew is the generic name for a series of fungal diseases affecting many plant species, but of epidemic proportions in some economically important crops, such as grapes, tomatoes, potatoes and squash. These diseases are caused by oomycete microorganisms related to the Chromista kingdom, and sometimes called “pseudo-mushrooms”.

For the record, the same mildew that is causing you hassle today has been responsible for famines, including the great famine in Ireland in the middle of the 19th century, with more than a million deaths. It allows to relativize our little worries in the garden, is not it ?

What does it look like ?

Mildew is characterized by brown spots or the appearance of white and cottony molds, followed by general wilting of the leaf, twig or whole plant.

What are the conditions of its development?

Mildew likes mild temperatures but not too hot, and moisture – it is favored by the succession of periods of high hygrometry (over 90%) and temperature variations between 11 ° C and 25 ° C.

There are different ones?

Yes, there are actually several kinds of parasites, including:

  • Plasmopara , which belongs to the grape mildew – Plasmopara viticola – native to America. His first known apparition in France dates from 1878.
  • Phytophthora , which includes the potato late blight (Phytophthora infestans) also native to America, which was responsible in the 1840s for the famine of the potato in Europe, and that of the tomato.
  • Peronospora , which attacks various market garden plants as well as tobacco, and Sclerophthora , which attacks cereals, sugar cane and various other grasses.

Why does mildew like potatoes and tomatoes?

Because these plants are among the most cultivated in the world, of course! As was said in A History of Tomatoes , 160 million tonnes of tomatoes are produced worldwide each year, and more than 380 million tonnes of potatoes! 12 tons every second. Not bad is not it ? As a result, many potatoes and tomatoes equal a lot of mildew.

This is Christopher Gatineau who says most clearly:

There is a golden rule in agriculture: the more a species is cultivated, the more the people who feed on it grow. It makes sense as peasant common sense. And pure juice: who would sit around an empty table? This is why monoculture concentrates all consumers of this crop.

There is another golden rule: without agriculture, humanity would be reduced to 5 to 10 million as 12,000 years ago. This is to say that monoculture is only a response to the feeding of nearly 8 billion heads. A good or bad answer, that’s not the question. But as monoculture intensifies, mildew thrives; especially since the potato is not indigenous but exotic. Inadapted!

Can we fight?

Before, yes, a little.

  • Promote air circulation between plants – rows of tight tomatoes will let mildew spread at the speed of a galloping horse, or almost! Conversely, the air that passes between the plants and between the leaves dries the plant, which does not leave much chance for spores of late blight.
  • Why not even plant your tomatoes or potatoes not necessarily in a row, not necessarily together, but scattered in the garden ? Okay, when it comes to harvesting, it looks more like a treasure hunt, but it limits the development of spores when they arrive.
  • A fairly complex but apparently effective solution is to house the tomatoes to limit the moisture on the foliage and the spread of the spores by the rain.
  • Remove the leaves that touch the ground because this area is usually wet, and it is also by the soil that the spores arrive.
  • Avoid watering at night – to avoid nighttime humidity. Prefer watering in the morning, avoiding foliage.
  • Do not replant in the same place the same plant species that were affected by late blight the previous year.
  • Finally, there are varieties less sensitive than others! Big defect varieties resistant to mildew: they are often hybrids , so seeds you will buy. We can not have everything ! But there are also some fixed and less sensitive varieties.

In case, if your plants are a little tight, and it rains one evening with mild temperatures, take care …

And in preventive?

According to some sources, it is possible to use as a preventive a manure composed of a garlic decoction – The allicin contained in garlic would have fungicidal and bactericidal effects, without harmfulness to the environment. How to do ? Bring to the boil 5 liters of water to which are added 15 cloves of garlic peeled and split in half. Let ferment, placing the container open and exposed to the sun for 4 to 5 days – until the mixture is frothy. Filter and spray on the leaves and soil around the plants to be protected. Does it work ? We want many testimonials, do not hesitate.

In healing there are not many solutions.

The traditional fight against mildew is copper-based, since the microscopic parasites that mildew causes – oomycetes – are extremely sensitive. Thus the Bordeaux mixture is a fungicide manufactured by neutralization of a solution of copper sulphate with slaked lime.

Well or not good Bordeaux mixture?

The Bordeaux mixture is authorized in organic farming. However, depending on the dose, it negatively affects the metabolism of most living organisms – animals, micro-organisms and plants, terrestrial and aquatic. Its toxicological classification is also very clear: harmful to health, dangerous for the environment . It’s clear?

Small note culture: do you know why it is called the Bordeaux broth? Because mildew also attacks the vine, is that it is in Bordeaux that it was born. Here.

Baking soda and soap?

Possible natural healing treatment, according to some, baking soda. You will find there comparative testswhich seem to conclude to a positive effect, on our side, one did not try, but one gives you the recipe:

The following mixture is sprayed on the infected plants:

  • A tablespoon of baking soda
  • 4 liters of water
  • 4 cl of horticultural oil or black soap – two tablespoons roughly.

Dr. Kanika Singla

Ph.D., IARI Postdoctoral Scholar, UC Berkeley

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