The Biosynergic approach: downy mildew at the center

As I expressed elsewhere, the management of the phytosanitary balance of the vineyard should not represent either the alpha or the omega of good viticulture. But it must be admitted that this has been the winegrower's primary concern since the end of the 19th century, since the European vine Vitis vinifera had to face American parasites (powdery mildew, downy mildew and phylloxera) against which it generally did not have the natural defenses conferred by centuries of natural selection... Among these parasites, it is obviously the downy mildew Plasmopara viticola which poses the most frequent problems and the most significant destruction of crops. Since the development of Bordeaux mixture, copper has been a major element in crop protection methods against various diseases (mildew, certain mycoses and most bacterioses), particularly on vines, fruit production and vegetable crops. Although it remains widely used today in various forms of so-called “conventional” agriculture, alongside other pesticides, copper plays a crucial role in agrobiological systems, because it is currently the only active substance approved in agriculture. biological (AB) having both a strong biocidal effect and a wide range of action. Although most uses of copper are justified by its biological effectiveness, they pose eco-toxicological problems (proven risks for soil microbial populations, earthworms, certain aquatic organisms and crop auxiliaries). The highlighting of these environmental impacts of copper has motivated regulatory restrictions on use (capping of applicable doses per hectare and per year), and even its ban as a pesticide in certain European countries (Netherlands, Denmark), which generates distortions of competition between countries. In November 2018, the European Commission voted for a new authorization for seven years of compounds derived from copper in agriculture, capping this use, from February 1, 2019, at 28 kg/ha over seven years, or 4 kg/ha/ year on average, compared to 6 kg/ha/year previously. We will return specifically to the subject of the toxicity of copper with respect to the environment. In the meantime, the increasing restrictions on authorized doses of copper as well as the persistent threat of a total ban on a European scale pose difficulties for producers, and more particularly for farmers in AB, who cannot resort to synthetic pesticides. . This results in a recurring demand for “alternatives” to copper addressed to research, which emerged around twenty years ago and remains part of recent research priorities. This question of “alternatives” to copper has therefore been the subject of numerous research and research and development work since the beginning of the 2000s, and of many research actions of more limited scale throughout the world. There are also numerous trials of alternative solutions, conducted by technical centers and producers, to assess the technical relevance of this or that molecule or preparation. Knowledge has also been acquired on the underlying biological mechanisms (induction of plant defense against pests, ecology of pathogens and biological control agents, etc.). In “Can we do without copper in organic crop protection?” Collective scientific expertise”, Andrion D and Savini I. (2019, Edition Quae) offer a clear synthesis on this subject. The biosynergic approach that I defend aims to use all the effective alternatives available in vineyard protection strategies, in particular against downy mildew, with in particular the prospect of developing replacement methods for classic copper. The available alternatives can be grouped into three main types. Methods with direct action on the pathogenic organism The search for microbial biocontrol agents is the subject of numerous studies. These micro-organisms can act directly on pathogens, notably insects but also certain fungi (Botrytis cinerea in particular), through antagonism, hyper-parasitism or ecological competition. In addition to their direct effect, some also have the property of stimulating plant defenses. Due to their particular characteristics (living organisms), their deployment is more complex than the application of chemical molecules, which can hinder their adoption and promote variability in their effectiveness in the field. Recent work therefore focuses on determining the optimal conditions for using these products, and identifying strains with high potential by exploring the complete microbiota present in the vicinity of the plants or organs to be protected. A complex but promising approach. The phytosanitary use of these products based on microorganisms also requires a long and costly marketing process. There are currently few approved products against pathogens targeted by copper, and the strains or species still at the upstream research stage are very far from covering the gaps and needs. There are therefore still few really serious and proven avenues for replacing copper with microbial biocontrol agents. The use of preparations or natural extracts with biocidal activity is also the subject of numerous studies. Often complex in composition, these preparations frequently have, in addition to their biocidal activity, an action to stimulate plant defenses (the case of many essential oils). Their strong antimicrobial activity under controlled conditions makes them serious candidates to replace copper, but their formulation remains difficult. Likewise, certain undesirable effects on the products harvested, and questions about the status of certain preparations with respect to AB specifications, make their use sometimes problematic. Orange, oregano and sage oils seem promising but silicon, in forms to be defined precisely and so dear to biodynamicists, certainly has poorly exploited assets. Plant defense stimulators are currently the subject of very active research Numerous products or molecules with proven biological activity under laboratory conditions have thus been identified. Many of them (phosphites, extracts of micro-organisms (fungi) and plants (algae), etc.) seem to have a multiple mode of action, with both defense induction effects and biocidal effects (cases in particularly phosphites) or direct disruptors. If these molecules often seem active in confined and controlled laboratory conditions, the transfer of this activity to the field often proves problematic, with weak or very random/irregular protections provided. This can come from difficulties in formulation (the products must be able to penetrate the plant to be bioavailable and perceived there), in the positioning of the treatment (a defense stimulator must necessarily be applied upstream of the infection, while many biocides are more effective when applied in the presence of the target parasite), perception of the signal by the plant, persistence of action, and even evaluation methods. However, these issues remain little studied, with most of the work currently being dedicated to the search for molecules or products with demonstrable effectiveness in the laboratory. Some trials of combinations of SDP and cupric products are encouraging against vine downy mildew, and it is now important to develop a rational basis to identify a priori the best combinations. As with other biocontrol products, not all SDPs can be used in organic farming: this is particularly the case for phosphites. These products have remarkable effectiveness against oomycetes (at least 70-80%) and are systemic (penetrate into the plant and are therefore not very sensitive to leaching by rain). Their classification as SDP is the subject of controversy: if their eliciting power is proven, at the doses used, their fungicidal effect is certainly preponderant. Another debate concerns their synthetic or natural nature: are they really more synthetic than the copper salts used in AB? We will discuss this specifically later. Phosphites, which were authorized in AB in various European countries (Germany, Greece, Austria, Spain, Hungary, Czech Republic) until September 2013, lost this authorization with their classification as a plant protection product, and not more fertilizing or biostimulating as before. They are unfortunately currently banned in AB throughout the European Union. Finally, remember that phosphorous acid, a product of phosphite degradation without toxicological connotation, accumulates significantly in harvested products and is subject to maximum residue limits (< 100 mg/kg of grapes) or import tolerances. and therefore does not make it possible to differentiate the use of synthetic fosetyl (aluminum ethyl phosphite) from simple sodium or sodium phosphonates or phosphites. Other pesticides approved in AB also leave residues in the final wine (Spinosab insecticide for example, sulfur in general, sulfur in general, copper also in certain cases….), this argument is therefore not really valid... The non-differentiation of the use of fosetyl vs. other salts is more admissible but so what? What about the manufacturing process of the different types of copper salts used in viticulture… are they really more environmentally friendly and sustainable…. ? We can wonder. The argument of the natural source (naturalness), fundamental basis of the inputs of organic and biodynamic agriculture, is not as solid a pillar as it might seem. If phosphonates were authorized in AB, we could convert 99% of viticulture overnight! Isotherapy, based on the principle of “treating evil with evil”, is frequently used, in various forms, in human and veterinary medicine (vaccination for example), and sometimes in plant health. Its main variation in plant health consists of using highly diluted and “potentized” (i.e. shaken for quite a long time) preparations of the pathogen or infected plants/organs. These preparations, based on living or dead organisms (ashes from the incineration of pests for example), are then sprayed on the plants to be treated. Other forms of isotherapy have also been used, sometimes with some success, in plant health. This is the case for protection protocols using attenuated strains of viruses or inoculation of plants with “hypo-virulent” strains of fungi. Homeopathy is based on a similar principle, but a little different by the absence of active ingredients sensu stricto It uses high dilutions of potentized natural extracts (from plants, soils, for example), some of which can be highly toxic at higher doses, and exploits the “memory of water”. Indeed, certain homeopathic preparations are so diluted that they can statistically no longer contain a single molecule of the original substance; proponents of this method claim that the activity of these preparations would then come from the capacity of water to preserve the molecular imprint of these substances. Biodynamics uses a set of nine preparations (named 500 to 508) whose recipes were described by the founder of the biodynamic movement, R. Steiner These are cow manure or finely ground quartz incubated in a horn (500 and 501) or plant extracts (502 to 508). These preparations, also highly diluted, are supposed to promote the growth, development and ability of plants to resist their enemies. They can be prepared by the farmer himself or less orthodox purchased from specialist suppliers. I discuss this topic in more depth in the article Why I Will Never Be a Biodynamist. Finally, let us point out the use of "proteodies", musical sequences supposed to interfere with the sequence of amino acids of proteins at the time of transcription of the genome of the plant or parasites, an approach widely publicized among the general public but whose scientific foundations are not known. nothing proven Methods based on homeopathy or isotherapy seem to be of very questionable effectiveness, and undoubtedly do not constitute a credible alternative to other possibilities. They are also the subject of very rare academic and technical publications; very little scientifically evaluable data concerning them is currently available. It is not the same if we get rid of the anthroposophic preaching of biodynamic priests! And yes, by no longer confusing knowledge and knowledge and by respecting the BABA of the experimental approach, we can scientifically demonstrate differences which until now only fueled sterile debates. Thus, more and more serious work is being carried out to compare and understand the differences between conventional, organic and biodynamic viticulture with extremely scientifically corroborated results. We will come back to this specifically. In the meantime and to conclude, the Biosynergic approach that I wish to promote claims an eclectic and totally antidogmatic approach. Its sole aim is to optimize the development and protection of the plant against biotic and abiotic stresses by using all means having a certain effectiveness directly or indirectly on the plant or its pests. These means must not have a negative impact on the environment near or far from the exploitation, but must place Man face to face with his responsibilities, not only ethical but also economic. Strictly natural solutions must of course be favored, but strict naturalness should not be a limit either if more effective alternatives that are just as respectful of the overall framework of the ecosystem are also available. Plant stimulators, biostimulants, nutrients, elicitors and potentiators of natural defenses, microbiota of interest, must therefore be used without limit, if I dare say so. But it is of course the maintenance, or creation, of an environment conducive to the healthy and harmonious development of plants and humans which must above all be prioritized. It's an easy idea to express and a more difficult task to achieve with the constraints of the modern world. Bio synergy here joins the fundamental principles of salutogenesis and biodynamics, freed from their esoteric dross by trying to place at the center the reason which we often lack.