In order to answer this question, I need to go back to a key point that I explained earlier in question 4 regarding the difference between organic and biodynamic. In biodynamics, disease is viewed differently. It is assumed that a pathogen (fungus, insect, bacteria …) is only a symptom that appears because of an underlying cause or existing imbalance. Thus, the notion of ‘fight a disease’ must be replaced by a new logic of ‘prevention and correction of imbalances’. Such reasoning suggests that if imbalances are reduced, the threat of disease should decrease. Vines are therefore better able to resist disease on their own, just like healthy individuals.
The primary source of imbalances in vines is precisely the accumulation of attacks from agrochemical treatments. What a contradiction! The products believed to ‘protect’ the vines are actually responsible in the long run for their increasing vulnerability to disease. And so from here the vicious circle of chemically-dependent agriculture begins: more chemical products lead to more disease which leads to an increase in the frequency and severity (and therefore, toxicity) of treatments, etc. It is often difficult to take the first step out of this logic because the winegrower is fearful of the risks that follow. One must break away from the use of chemical products. This is the most critical stage, known as the conversion phase, and lasts three years. During this time one must be extremely vigilant. Restoring balance is indeed a gradual process.
Let us go back to the logic which lies behind preventing imbalances. The great majority of preparations used in biodynamics are derived from plants. These plants are generally infused in water, then diluted, and finally dynamised (see question 12: What is dynamisation?) in a larger volume of water before being sprayed on the vines either with a hand-held sprinkler or a tractor. The logic behind these dynamised plant infusions could be compared with that of homeopathy: it involves a quantity of relatively diluted and dynamised plants. Unlike chemical products, these preparations do not act on a quantitative level, but rather on another level, let us say energetic. In any case, it is a level unrecognised by modern science.
It is important indeed to understand that the reasoning which guides the choice of preparations used is not scientific. It involves analogical or symbolic reasoning. Scientific logic analyses the causal chain, or the cause and effect relationship. Then, based on the principle that the same causes produce the same effects, one tries to understand and quantify the action mechanisms of various molecules. Conversely, analogical or symbolic reasoning leaves a great deal to intuition and the global perception of phenomena, without concern for the specifics of a mechanism (see question 10: Is biodynamics scientific?).
Let us take the example of horsetail infusion which is frequently used in biodynamics. Horsetail is a small plant that generally grows in very moist soils but which, surprisingly, has very restrained growth despite the abundance of water. Its structure is quite hollow and the stems and leaves look like hard, dry needles. They contain an enormous quantity of silica, rather than water. Horsetail is essentially the opposite of a water plant (the water lily for example, whose structure cannot even resist gravity). Thus, a brief observation shows that one of the essential qualities of horsetail is to successfully manage excess moisture, while remaining dry and maintaining its vigour. It is this quality of the plant that the winegrower seeks to transmit to the vine when he sprays the infusion. For this reason it is often used during wet springs. Horsetail shows the vine how to avoid excessive growth associated with an overabundance of water, which would otherwise lead to a significantly higher vulnerability to mildew. Intuition is not enough, of course. You need to test the procedure to confirm that the idea works. Such is the case with horsetail which is used by many growers.
The great majority of biodynamists continue to use copper and sulphur as a supplement in improving plant and soil equilibrium. Although these products are not produced synthetically and are less toxic and unbalancing, I consider them to still be part of the former ‘fight a disease’ logic. Copper is principally used to prevent downy mildew while sulphur is used against powdery mildew (here I am referring to sulphur sprayed on the vine, and different from sulphites used in the winery during vinification and which will be discussed in question 17: Does a biodynamic wine contain sulphur?). Even if most biodynamic growers set increasingly strict targets to reduce the quantity of copper and sulphur they apply, their use is still based on quantitative logic, which is to say, adapting the dose to the severity of the disease.
It should be noted that certain producers, in certain vintages, on certain parcels, succeed in growing their vines without copper or sulphur. In my opinion, these experiences are and will be the main subject of viticultural research today and for years to come.