By
Ludivine Laniepce
Published on
May 14, 2024 at 6:46 a.m.
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She carefully travels the tourist route behind the wheel of her car. Dominique Diaz, crop advisor on the west coast for the Manche Vegetable Producers Group (GPLM), probes the embankments and plots with his eyes: “It’s in there. The nutsedge is hidden everywhere!»
In this month of May 2024 in the vicinity of Créances (Manche), this bright green young plant comes out of the ground. Currently a few centimeters high and resembling grass, it is nevertheless preparing to wreak havocin certain cultures, particularly those carrots being planted.
Because Cyperus esculentus is an authentic plant of mass destruction. “The nutsedge is an invasive species today present throughout the world and in all production areas in France,” explains the technician. He is considered as the 4e global plague . »
“The 4th world plague”
The primary strength of the tiger nut lies in its ability to vampirize the earth,particularly that of vegetable ponds, multiplying rapidly.
It is capable of germinating up to 40 cm deep. A single strand sends underground stems all over the ground. The rhizomes emerge into the open air and a new sprig grows. The nutsedge also has tubers the size of a pea, a sprig can produce around fifty and they can stay in the ground for up to 7 years. Several square meters of soil can be infested in a field in one season.
The root system of the nutsedge is such that it smothers that of carrots, leeks, potatoes and even corn , limiting or even making their development impossible. “There are three nutsedge harvests per year,” notes the technician. The first, the most grouped, is taking place at the moment. But there are now so many tubers of all ages in the ground that we no longer distinguish these periods. »
Although this perennial plant is almost unknown to the general public, it has, however, been driving producers into a frenzy for several years. Because the second strength of the tigernut is that it does not exist to this day no human, mechanical or chemical means known to fight against him.
“60% loss per plot”
In Denneville, retired market gardener Alain Langlois treads a plot intended for carrots inherited from his father and now exploited by his daughter. Like others, for a long time, he did not pay attention to these “tufts” that he weeded here and there.
“Quack grass, nightshade, fumitory, panicum, etc.,” he lists, “we always had a chemical solution. Today, nutsedge scares us because nothing works about it and there are fewer and fewer active ingredients that we can use. There, we realize that our herbicide coverage had a double effect because it slowed it down a little. Now we’re tinkering. When we try as best we can to control it, it is approximately 60% loss per plot. We feel helpless. »
Alain Langlois estimates that “three quarters of producers who have held out so far, particularly young people”, will reduce their cultivated areas, will modify the nature of their crops or cease their activity due to the withdrawal of herbicides and the uncontrollable expansion of nutsedge. “The public authorities will perhaps react when yields decrease, but it will be too late,” he regrets. What I want is for us to be given a solution, whatever it may be. »
If the young retiree remains optimistic, others are resigned or rage against “ general indifference faced with the damage from nutsedge” and “the considerable delay by the authorities despite long-standing reports”. “Do you realize that they sell it in garden centers? That we talk about it without ever saying the consequences it has for us? It’s unbearable and irresponsible!, complains another market gardener from the surrounding area. The loss of competitiveness is enormous. »
Around ten uncultivated hectares
In 26 years of presence in the production area on the west coast, Dominique Diaz, a patient, pugnacious and passionate observer, has imagined everything she could to uncover the secret of tiger nut and detect its flaws: rotation and introduction of new crops , animal competitions, electric weeding, sieving, phytosanitary products, deep plowing, grinding the soil, manual weeding, essential oils, microwaving and baking tubers, inspection of thousands of droppings… In vain. The tiger nuts are always coming back stronger and dictates its law.
Laser weeding is starting to develop in certain countries but the costs are prohibitive and the programming is not yet complete because it involves artificial intelligence. With electric weeding, we barely managed to knock out the nutsedge. during two months. He then comes back as if nothing had happened. But it allowed us to get out carrots that wouldn’t have come out otherwise. The nutgrass is the acme point for us in the more general problem of weeding, the protection of crops which are starting up in the face of competition from weeds with fewer and fewer means of combating them.
The technician places the tipping point around 2018: “When the herbicide products were withdrawn, we saw that we no longer controlled anything. They helped relieve the pressure a little. There, 100% of plots are reached.We have around ten hectares which are uncultivated on the west coast, carrot producers who have abandoned plots, market gardeners who have permanently ceased their activity due to the withdrawal of herbicides and the infestation of nutsedge. It can make land waste in two years. We must find a solution at all costs. , otherwise it’s over. But it is developing much too quickly and in my opinion, there is always a dispersion bias that escapes us. »
Trial plots
In the honeys of Créances, these cultivated sands which border the sea on either side of the dunes, Dominique Diaz tells the story of these plots shaped by the hand of man, strongholds of the emblematic sand carrots and leeks: “ The ancients had come from the land to farm in the sand because weeding was more manageable. » The nutsedge, which thrives in a sandy substrate, has spread there over time.
Among the preserved plots, partially affected or totally infested, one of them attracts attention. This winter, nothing suggested that by May, it would be irrecoverable. Invaded by nutsedge, it now serves as a test plot at Sileban, the vegetable experimentation and development station in Normandy, to carry out new experiments.
A hope ? Maybe. But there is urgency. Because the third strength of the tiger nut is itsformidable capacity for adaptation.“My theory is that this plant is a garden escapee,” says Dominique Diaz. The first infestation area that I observed was in Bretteville-sur-Ay. Today, I see him at Les Pieux in Bréhal. »
A 4th experimental program in progress
If nutsedge is today present on all continents, France, unlike the Netherlands, Canada or Switzerland, which are particularly active, was slow to get involved. However, the stakes are high: everywhere, nutsedge reduces the yields of market gardening and field crops.
In the English Channel, Sileban, the Normandy vegetable experimentation and development station, is currently carrying out its 4th program on this invasive plant. “From Port-Bail-sur-Mer to Agon-Coutainville,” she relates in her latest assessment, “the nutsedge is present in 36% of the 1,000 hectares of production in the west coast basin, an increase of 15%. compared to 2015. Heavily infested areas are increasing and represent 12.5% of the basin. » In Bretteville-sur-Ay, Glatigny and Surville, there are no longer any healthy plots.
Julie Leroy, program manager with GPLM and Agrial, locates a main focus on the west coast and a few in Val de Saire. With technical advisors, she works to deepen the still superficial knowledge of the biology of this plant, to identify its presence and to seek solutions to eradicate it and protect crops. “Plant protection products don’t do anything,” she notes. We report the problem to the companies but we cannot find a molecule authorized in France that is effective. » In the field, new experiments are underway, particularly at Créances. They combine electric weeding at different stages of the nutgrass and sieving of the soil with several extraction tools.
The dispersal of the nutsedge, native to the Mediterranean basin, remains sneaky. Nutsedge may have traveled clandestinely in the bulbs of other plants, notably from Spain or the United States. Added to this hypothesis is a certainty: it then easily colonizes fields by getting stuck in machines, tires or shoes. “There is awareness work to be done to preserve free areas as much as possible,” adds Julie Leroy. Clean the equipment if possible to avoid any further contamination. The longer we wait, the more risk there is for other areas. Any presence of nutsedge must be reported to technical advisors and to FREDON. »
And he advances inland. In its latest study on the evolution of nutsedge in the west coast basin, Sileban notes, at the end of 2022, “an extensive and proven risk” of progression in sectors such as Saint-Germain-sur-Ay, Angoville-sur -Ay or even Lessay “where the nutsedge could proliferate significantly” and “an alarming development in the west coast basin”. Dominique Diaz quips: “We haven’t finished putting up signs upside down…”
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