2.4.4.b.b Decoctions

A decoction is an extraction practice for active principles and/or aromas using hot water. The product is immersed in water which is then brought to a boil over a fairly long period. Unlike an infusion, it involves the solid parts of the plant, notably the roots, stems, seeds and/or bark. This extraction practice contains more active principles than an infusion. The decoction time may vary, as well as the quantities of plants that are used, but the process of making a decoction remains the same:

Cut the plants into coarse pieces
Let them soak for 24 hours in water
Heat and keep simmering for 20-30 minutes (80-90°C) covered (to avoid letting the essence-rich vapours escape)
Allow to cool without removing the lid
Filter and add to the treatment mixture

Horsetail decoction

Horsetail (Equisetum arvense) acts as an antifungal (anti-germinative) against downy mildew and black rot due to its high silica and antioxidant (flavonoids and phenolic acids) content. Other enzymes contained in horsetail such as HTG (Hetero-Trans-Glucanase), unique to the genus Equisetum, enable cell walls to thicken. Thiaminase also seems to repel insects.

Dried horsetail

It is preferably applied in the morning or late afternoon. (Simple nozzles, medium drops, directed at the ground). Care should be taken in its use as it can have a drying effect.
The dose is 100 g/ha of dried plant. It can be applied to the soil as a preventive measure in spring, usually before Easter. Another application is possible at the separated flower bud stage if there is a medium to high risk of downy/powdery mildew. A final application in the autumn following the harvest helps to prevent wood diseases.

Source: Kuzheng, 2013

Horsetail compounds and how they work: Silica is an active material that plays many roles:

This element acts as a physical barrier and prevents hyphal invasion of downy mildew
The Si element would have a "light effect": it has an impact on plant growth with an effect similar to that observed in plants exposed to light
Si, as a cross-linking agent, improves the plant wall's mechanical properties and ensures the cell shape is maintained.
Si in the form of silicic acid allows the induction of the biosynthesis of defence substances (PDS)
The Si element also has an effect on the mitigation of abiotic stress suffered by the plant, as well as on the mitigation of nutritional disorders

Horsetail antioxidants are phenolic compounds that act by stimulating the plant's defences. Flavonoids and phenolic acids reduce the pathogen's growth. Spraying with horsetail decoction stimulates the production of phytoalexins in the plant and activates its metabolism for the synthesis of phenolic compounds. Finally, the HTG enzyme strengthens the plant tissues and increases the resistance, hardness, thickness and rigidity of the epidermis.

Oak bark

Oak bark can also have an effect against cryptogamic diseases. Its use is only recommended in very wet periods when there is a significant threat of downy mildew. An initial application can be made following flowering, as this will inhibit the development of downy and powdery mildew mycelium.
The dose is 50g/ha and with a decoction simmered for 20 minutes. It is recommended to apply only one treatment per year if necessary. It is not recommended to use this preparation on vines that are very young or weak, as it could check growth.

Alder buckthorn bark

Applied after flowering, alder buckthorn decoction inhibits the development of downy and powdery mildew mycelium. It helps the vine to produce stilbenes which are very toxic for mildew due to their high anthraquinone content. The recommended dose is 120g of dry plant/ha. An alder buckthorn decoction can also be combined with a decoction of horsetail or oak bark for example. The maximum mixture dosage should not exceed the recommended dose for a single plant.

The active ingredients of alder buckthorn and how they work: when attacked by a fungus, the plant receives a "warning signal" and sets up a defence mechanism against this pathogen by the synthesis of stilbene phytoalexins (resistance markers). These phytoalexins, considered to be among the vine's most effective responses during fungal infection, have a biocidal and fungistatic effect against downy mildew (plasmopara viticola) by reducing the mobility of the zoospores. However, the plant can take time to synthesize these molecules after recognition of an attack and therefore does not fight the fungus immediately. Spraying with alder buckthorn, which is rich in anthraquinones (emodin), reduces the fungus's mobility by inducing the synthesis of stilbenes by the plant. Alder buckthorn is a "base substance" that can be used as a preventive measure, in addition to the usual treatments in order to reduce the risk of mildew attacks, but it also acts by stimulating the plant's defence mechanisms (PDS) through the increased production of stilbenes.

Other plant extracts such as rhubarb roots have an antifungal effect. It is also used against downy mildew in order to reduce doses of copper. Alder buckthorn and rhubarb have an eliciting effect on the plant's natural defences and a biocidal effect on mildew.

Summary table

Plant	Used plant parts	Category	Active ingredient	Objective(s)	Mecanism(s)	Application stage	Dosage
Horsetail	Entire plant	Basic substance / NDS (Silica)	Silica, formic acid, HTG, thiaminase	Humidity control	Cryptogamic and wood disease resistance, foliage resistance	From budburst to flower buds clusters. Following harvest	100g PS/ha
Oak	Bark	Biostimulant	Calcium	Humidity control	Cryptogamic disease resistance	Following floraison up until the size of a small pea	50g/ha
Buckthorn	Bark	Biostimulant, NDS	Tannins (Stilbenes), Anthraquinones (emodin)	Humidity control	Cryptogamic disease resistance	Following floraison up until the size of a small pea	120g PS/ha

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