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Downy mildew ravages certain crops, especially tomatoes. (©Adobe Stock)
A white film on the underside, leaves that end up necrosis. Lovers of vegetable gardens and market gardeners have undoubtedly noticed it: in recent times, tomatoes and some garden vegetables are the target of late blight, a microscopic fungus that gradually destroys plants.
“80% of my tomato harvest will be lost, representing 60% of my turnover for the season” laments a market gardener near Honfleur, in the columns of the Pays d’Auge. He is not the only one.
With the capricious weather in recent weeks, tinged with rain, this fungus is proliferating in crops. Explanations.
What is late blight?
Phytophtora infestans : this is the scientific name of this mushroom, which is characterized by spots that appear on the leaves, fruits and stems of the plant.
Most affected? The vines, the potatoes and especially at the moment, the tomatoes. A phenomenon all the heavier as we are in the middle of the fruit season.
“Normally, mildew appears between April and June. The, we are in high season, it is therefore very difficult for market gardeners whose crops are affected by this disease, ”explains Alain Demanneville, gardener specializing in permaculture, near Honfleur.
Blame it on the weather
If the mildew usually occurs before the summer, it would appear to be playing extra time in 2021. The reason? Rain episodes of the last few weeks. The Weather Channel indicates that the precipitation for this month of July 2021 is over 30% on average in France.
Downy mildew develops mainly because of humidity. We have had a very chaotic season, the off-season is coming sooner than expected.
All of this combined with wind episodes that spread the fungus spores. And mildew which spreads very quickly.
A disaster for the vines
This year, mildew has hit the vines hard. As such, the Interprofessional Committee of Champagne Wine (CIVC) estimates that these “attacks” have generated between 20 and 25% of losses on the scale of the 34,000 hectares of the Champagne vineyard, said Agence France-Presse Tuesday 27 July.
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What are the means to limit the damage?
Unfortunately, when late blight took the plants by storm, It is already too late. ” This is a very rapid illness, blows the gardener, sometimes in a day. She’s already done a lot of damage. There is no miracle solution to eradicate it completely ”.
Nevertheless, there is some tips to prevent mildew from appearing in crops. Here they are :
- Space the plants to ventilate well because humidity favors the appearance of downy mildew
- Water in the morning rather than in the evening to avoid excess moisture
- Avoid permanently wet planting areas
- Rotate crops every four to five years
There are also a few techniques for treating late blight to “limit the damage”. First the bicarbonate (a tablespoon to dilute in a liter of water before spraying on all the leaves), then the Bordeaux mixture, composed of water, copper sulphate and lime to be applied (via spraying) regularly from the beginning of spring.
Last solution finally: wait for the sun to point the tip of its nose several days in a row so that the plants healing naturally.
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