Since gardeners do not have the right to protect their plants by synthetic pesticides, the “preparations” natural “to base of stinging nettle, horsetail, tansy, comfrey and a variety of plants are, more than ever, presented as one of the solutions in order to fight against bio-aggressors” (diseases, insects, etc.).

The sites and magazines specialized in gardening makes a genuine apology to these “natural medicines” which they dedicated articles and special folders. The nettle fertiliser, for example, is sometimes presented as a “very good anti-harmful for most pests such as aphids, sometimes, as a “repellent” able to scare the worm (or worm) of the apples or prevent the onset of the very dreaded late blight of tomato. The decoction of horsetail would, in turn, a preventive and sometimes curative, against many fungal diseases (downy mildew, powdery mildew, scab, blister,…)”, not to speak of the extract fermented fern “effective”, against “the aphid (even lanigères) and the ciccadelle of the vine” with, in addition, a “repellent” against the insect of the potato, yet so difficult to combat.

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The manufacture of a liquid manure of nettle is easy to achieve yourself. 151097119/fotoliaanjak – stock.adobe.com

the question, of course, is whether these remedies are at the height of their reputation and allegations made by their followers, or their manufacturers. Because these funny “herbal teas” are sold a bit everywhere. The garden centres market for many years, preparations, ready to use, at prices between 5 and 10 € per litre, depending on the volume of purchase and packaging. You can even find on the Internet of the nettle fertiliser “concentrate” sold 16,90 euros for a packet of 250 grams. A little bit expensive, especially when it is so easy to make these potions yourself…

In theory, the idea of healing plants with plants is far from being far-fetched. After all, many of the drugs successfully used in human medicine, such as digitalis or the irreplaceable ointment at the base of arnica are derived from plants. But, in practice, the promised results are nowhere near as spectacular as what we could hope for.

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First finding: contrary to the claims of their proponents, the herbal preparations, including the maceration of nettle very often put forward, are not an agricultural practice of ancient or traditional delivery to the taste of the day. In a study published in 2012, the national Society of horticulture of France (SNHF) found that neither Cato the Elder, or Olivier de Serres, or Jean-Baptiste de La Quintinie, agronomists of reference which have succeeded one another from Ancient times up to the time of Louis XIV do not mention it in their writings. In the last century, the nettle begins to be cited in the extensive bibliography consulted by the SNHF, but only for its uses in pharmacy human food (the soup of nettles is a treat!) or textiles. In fact, it was not until the early 2000s, to see the alleged virtues plant the nettle has to be included in some journals and extension. If tradition there is, it is obviously very recent…

>> READ ALSO – learn how to recognize the parasites of your plants, The horsetail 52588568/aksinya – Fotolia

Second observation: the analysis of the results of fifty experiments carried out in France, from the end of the 1990s, by the Centre technique interprofessionnel des fruits, and vegetables (CTIFL) and the Institut français de la vigne et du vin (IFV) on different vegetable crops, condiment and fruit as well as viticulture, with several types of macerations of plants (nettle, horsetail, fern, comfrey, etc), proves disappointing. This is to control diseases (blight, rust, powdery mildew) or pests (aphids, slugs, beetles), no significant effect could be highlighted. And when interesting results are obtained on a site, it is impossible to replicate elsewhere or with other cultures.

“This is what happened at the end of the 1990s in the Gard, when tests conducted on downy mildew and black-rot of the vine have shown that applications of effluents nettle and horsetail gave promising results, we gave Daniel Veschambre, member of the scientific council of the SNHF, after the release of this study, which is one of the authors. At the time, the news had generated a lot of enthusiasm. Unfortunately, none of the tests conducted later in other regions, especially those where the parasitic pressure was stronger, did not highlight any effectiveness”.

No tangible proof Foliage and flowers of comfrey. Valentin Kosilov aka ArgenLant/argenlant – stock.adobe.com

Even hope disappointed with the maceration of the fern used against wireworm on potato. The positive results achieved in 1999, always in the Gard, have never been able to be confirmed by the following. Moreover, the experiments carried out abroad are not much more conclusive. “It is surprising to see the difference between the measured effects -void, useless and/or random – and the requirements on the use of effluents”, concluded, at the time, the document of the SNHF.

Since nothing has changed. No new experimentation carried out in the rules of the art has not provided the tangible evidence of an effect of constant, repeatable and reproducible from one year to another, from one place to another or from one experimenter to another. The reputation of the suspension is based, in fact, mainly on the return of experience of growers in which “it works”. But although it is not known if these results, are not exempt from subjectivity, are the product of chance or of circumstances advantageous.

Authorities little cautious

“In fact, the manufacturers of these products that come in the category of natural preparations of little concern to use of plant, or PNPP, are not required to prove their effectiveness, says Daniel Veschambre. In contrast to plant protection products in conventional, their consent to the placing on the market shall be issued without that they are subject to official tests carried out or controlled by third parties.” In fact, the administrative authorities are pretty little cautious: as long as the specialties that we submit them, pose little risk to human health or the environment, they give their green light.

tansy Flowers. 121699335/Pascal Cointe – stock.adobe.com

so, one can argue that if they don’t do well, these “medicaments natural” does not make it wrong either. “It’s a bit like homeopathy, except that with plants there is no placebo effect”, emphasises Daniel Veschambre.

Rich in nitrogen nitric, as most of the herbaceous plants, the leaves of nettles, comfrey or rhubarb, for example, properties, fertilizing undeniable. Exactly as would, incidentally, a chemical fertilizer type ammonium nitrate… The plants are healthier, they will be better able to resist the bio-aggressors, but will not be immune from the massive attacks of downy mildew, aphids, or cylindrocladiose, in the case of the boxwood, as it occurs in some years. In other words, it is of biostimulants that can possibly act in a preventive manner, but in no case of fungicides or nsecticides on curative effect, as you can still read it or hear it.

Solution for the future

Fortunately, there are alternatives that are more serious to synthetic pesticides are under study, starting with genetics. “The development of varieties resistant or tolerant to bio-aggressors is the solution for the future,” says Laurent Jacob, chargé de mission “crop Protection”, in Astredhor, the technical institute of the horticultural industry, citing the case of the Impatiens walleriana ‘Imara’, resistant to downy mildew and award-winning at last year’s Salon du Vegetal in Nantes. We may cite, also biocontrol products, in full development, the auxiliary natural or introduced (ladybug, ground beetle, larvae of lacewings…), trapping with sex pheromones, the natural pesticides (yes!) as the carpovirusine, very effective against the codling moth or stimulators of natural defences of plants. But the effectiveness of these “elicitors” (bacilli, which are substances of plant origin…), very dependent on the conditions of use, seems to be for the moment reserved for professionals or gardeners warned.

On your agenda: rendez-vous “garden” not to be missed

• may 24: scientific Symposium “Plants and the French Riviera, the carnival of the senses”, organized by the SNHF, parc Phoenix, Nice (Alpes-Maritimes).

• 25-26 may: Fête des plantes, chateau du Pin, Champtocé-sur-Loire (Maine-et-Loire).

PAO IMAC

• 25-26 may: 32nd Days doullennaises of the pleasure gardens on the theme “women and plants”, Citadel of Doullens (Somme).

• Until may 28: Participate in the contest “Gardening Otherwise, share your practices” by signing up here.

• Until may 31: the Training offered in several cities in France by the association Jardinot on themes “companion Plants, crop rotation, hedgerows varied…” and “weeding without chemicals, it is possible!”.

• Until may 31: 5th photo contest epidemiological surveillance 2019, organized by the SNHF on the theme of “Webs, cocoons and filaments”. Award ceremony on 14 June.

• 1 and 2 June: 26th feast of gardeners and 20th winners of the book award of garden P. J. Dreaded, chateau of Lude (Sarthe).

• 6 to 9 June: 16th rendez-vous “Gardens, Garden”, parc des Tuileries, Paris.

• 7, 8 and 9 June: 17th edition of the “Rendez-vous in the gardens”, organised under 3000 gardens of France and Europe by the ministry of Culture on the theme of “animals in the garden”.

• From 7 to 10 June: 19th “Day of pink” sponsored by Stéphan Bern, abbaye royale de Chaalis, Fontaine-

Chaalis (Oise).

Marianne Seguin & Cie

• 8-9 June: 11th day of botanical “green” future, alpine botanical garden of the Jaÿsinia, Samoëns (Haute-Savoie).

• 8-9 June: 7th Weekend “the rose”, parc de Bagatelle, Bois de Boulogne, Paris 16th.

• Up to June 9: annual opening of the conservatory of the peony, all the days of 12 h to 18 h, except Wednesday, chateau de Sourches, Saint-Symphorien (Sarthe).

• 14, 15 and 16 June: Feast of the creation and of the métiers d’art, Château de Saint-Jean-de-Beauregard (Essonne).

• Until 30 June: please Send your application to the national Competition of gardens in 2019, by clicking here.

• Until 8 September: Exhibition “the Gardens, the joys of Val d’oise”, the House of Doctor Gachet, Auvers-sur-Oise (Val d’oise).

• Up to 6 October: Exhibition “Arte Botanica” performed by 15 artists, including Rebecca Louis Law, Domaine départemental de La Roche-Jagu, Ploëzal (Côtes d’armor).

• Up to 13 October: Exhibition of sculpture “after nature” by Marc Didou, domaine de Trevarez, Saint-Goazec, (Finistère, brittany).

• Until October 15: Exhibition of 60 sculptures of Stone Treilhes in the Gardens of Eyrignac in Dordogne.

• Until 3 November: the 28th edition of the international garden festival on the theme of “Gardens of paradise”, the Domain of Chaumont-sur-Loire (Loir-et-Cher).

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