Essential oils | These are plant-based sprays used in organic and Biodynamic viticulture. They can be added to copper- and sulfur-based sprays (for downy and powdery mildew respectively). Rates are around 10ml per hectare.

The use of essential oils of the type used in aromatherapy is increasing amongst wine-growers, especially in France. The volatile aromatic compounds in essential oils can play a role in repulsing insect pests, and stimulating crop resistance to fungal disease organisms. The aromatic compounds are expressed either by pressing (cold extract) or by distillation in steam. Examples include: eucalyptus, used early in the season against downy mildew; palmarosa against fungal disease organisms; fennel and lavendin [sic] to repulse various insect vectors; garlic and fennel against the grape berry moth. Essential oils of thyme or clove can even be used against frost (see Valerian Tea). Sage, citronella, Sylvester pine, grapefruit, and eucalyptus are other bases for essential oils used in viticulture (Pierre Masson: 2014, p.168).

Only tiny volumes of raw material are needed, one or two heads of garlic or a handful of rosemary stems per hectare of vines for example. Cold extracts are made by crushing and macerating the raw material in olive oil for a couple of days and then decanting the oil into a bottle containing a fatty substance to emulsify the active ingredient so that it mixes in water ready for application. Cold extracts are said to retain a greater range of active elements than when either steam or hot water are used.

Essential oil sprays can be used sparingly around the perimeters of vineyards (the oils are very costly to buy), or on just a few vine rows per plot, and infrequently, as deterrents. Most growers use them only up until véraison so as not to affect the taste of the wine. They are photosensitive (light sensitive) so must be used in the evening.

Examples | Eucalyptus (to treat mildew), lavendar (to discourage insects), palmarosa (mildew). 

Bibliography

Monty Waldin,. Biodynamic Gardening (Dorling Kindersley, 2015).

Monty Waldin,. Biodynamic Wine (Infinite Ideas, 2016).

Pierre Masson,. A Biodynamic Manual (2nd edition 2014, Floris), p.168