When should vines be sprayed?

Even if this is often the colloquial expression: It is not the wine as a drink that is sprayed (except in Austria, where it means mixing the wine with mineral water), but the plant - i.e. the vine in the vineyard.

Spraying the vineyards serves to Plant protection. The vines and grapes have a lot of natural enemies, such as bacteria and viruses, fungi, insects, birds and wild animals. There are chemical and biological plant protection products to combat such diseases and pests, which are usually applied in liquid form. A distinction is made between spraying and watering: Watering means that the pesticide is mixed with water and applied to the vineyard, while spraying means that the mixture of pesticide and water is applied with the help of a stream of blown air. Depending on the fineness of the resulting droplets - depending on the nozzle used - this technique can be further differentiated between spraying, spraying and fogging. Spraying requires around 50 to 70 per cent less water than watering.

The following explanations refer to all types of application of liquid plant protection products. Very important: This is only general advice and cannot stand alone. Before using any plant protection product, it is essential to read and observe the hazard labelling (environmentally hazardous, harmful to health, toxic) and the instructions for use under all circumstances!

Effect of plant protection products

Plant protection products (Pesticides) can be divided into Fungicides (which act against fungi and may contain sulphur and copper, among other things), Bactericides (which act against bacteria), Insecticides (which act against insects) and Herbicides (which act against weeds ). As all of these agents kill life(microorganisms, animals and/or plants) and have an effect on the ecosystem in the vineyard, it is essential that they are used responsibly. This requires knowledge of the mode of action and application of the pesticide as well as proper equipment and operation of the application equipment. In addition to the correct dosage of the product - exclusively in accordance with the authorised application rate (kg/ha or l/ha) - proper storage and disposal, the prescribed distance from bodies of water and the necessary user protection must also be observed. This is because chemical plant protection products in particular can also have a toxic effect on beneficial organisms and crops as well as on groundwater and thus on humans and animals in general - apart from the health risks that may exist for the user during use.

The effectiveness of plant protection depends on a variety of factors. These include the weather, the time of day, the spraying or fogging technique (nozzle, pressure, fan type, arrangement and setting), the stage of development of the vine (and the associated foliage density), the mode of action of the product and the risk of disease or pest infestation (infestation pressure). The quantity used, the pH value of the water and the droplet size also play a role in determining success.

Timing and frequency of spraying

To get an idea of the proportions: All green (i.e. worthy of protection) parts of the vine - leaves, shoots and bunches - reach a surface area of 30,000 to 40,000 square metres, depending on growth vigour, grape variety and vine training surface area of 30,000 to 40,000 square metres per hectare. The leaf area, which can be extrapolated on the basis of shoot length growth, is decisive for the dosage of the plant protection product: In years with normal weather conditions for the growing region, the leaf area per shoot (shoot of the vine) grows by around 400 square centimetres within ten days. After this period, according to a rough rule of thumb, a new treatment is required to protect the newly grown parts of the plant. However, leaf area growth in the vegetation period between the end of May and the beginning of August is also heavily dependent on the weather, so that plant protection work must be adapted to the respective conditions each year.

The timing of plant protection work is based on relevant forecasts of how likely diseases and pests are to occur in the year in question. To this end, it is necessary to constantly monitor the vineyards for corresponding symptoms. It is also crucial to continuously monitor the relevant weather factors that increase disease pressure (see below); this is possible, for example, with the help of local weather stations. In addition, the development of certain animal pests, such as the grape berry moth, can be monitored by laying eggs in small cages and/or using pheromone traps.

The use of plant protection also depends on whether the winegrower works conventionally, integrated or organically:

• In conventional viticulture, plant protection is prophylactic and rather undirected using (at least predominantly) chemical agents: According to precise calendrical plans, often dictated by the agricultural industry (the manufacturers of the agents), pesticides are applied regularly as a preventive measure without monitoring the development of diseases or infestation by pests. Negative effects on the ecosystem in the vineyard are not taken into account. However, this form of viticulture is becoming increasingly rare.
• Integrated plant protection relies on a combination of mechanical, physical, biological, biotechnical and chemical methods, whereby chemical plant protection should only have a supplementary effect. The measures depend, among other things, on the weather, the stage of development of the vine and the previous year's infestation. Constant observation of the vineyard and the weather is of particular importance here.
• In organic or ecological viticulture only organic plant protection products are used. Herbicides are generally prohibited, and other means of protection against insects, animals and micro-organisms are preferred. However, certain fungal diseases can be most effectively combated or prevented by applying fungicides containing sulphur or copper. Fungi thrive particularly well in a warm and humid atmosphere, and with the help of modern meteorological methods it is now possible to predict weather developments quite reliably. More and more winegrowers are therefore only using plant protection products when there is an actual risk of disease (in technical terms: when the fungal pressure increases).

In the warmer months of the year, it makes most sense to apply the active ingredients in the early morning or evening. In order for the droplets of the active ingredient/water mixture to reach the plant surface and adhere to it, the humidity must be sufficiently high, otherwise the water in which the active ingredient is dissolved can at least partially evaporate in the air, resulting in insufficient protection. Furthermore, the active ingredient then needs time to penetrate (approx. 15 minutes as a guide).

The duration of the product's effect - usually between 6 and 21 days - therefore depends on the weather(rain washes the active ingredient off again), the time of spraying (see above), the effectiveness of the wetting (application quality) and the amount of active ingredient left over from the previous treatment. Now that integrated and organic viticulture are becoming increasingly popular, biological plant protection products are also being used more and more. However, as these are less aggressive than chemical pesticides, they need to be applied more frequently: The agents are more environmentally friendly, but the frequency of their use is higher.

Examples of fungal diseases: Powdery and downy mildew

The greatest danger to vines and grapes comes from fungal diseases such as powdery mildew and downy mildew. These are therefore considered here as examples with a view to plant protection.

Powdery mildew (Oidium)

Symptoms include

• reddish-brown to brownish-purple, irregularly branched spots on one-year-old wood
• infected buds(eyes) sprout with a white fungal coating
• grey-white, floury coating on all green parts of the vine
• musty odour in the vineyard

favouring factors:

• warm weather with high humidity
• Temperature of 21 to 26 °C
• Humidity of 50 to 95 %

preventive cultivation measures:

• airy training of the vines
• conscientious foliage work
• regular checks for symptoms

preventive treatment:

• during budding: treatment with two per cent net sulphur (guideline value 3 kg/ha)
• most important treatment period: 10 days before flowering (usually at the end of May), start of flowering (usually at the beginning/middle of June) and at the end of flowering (when approx. 80 % of the flower caps are open)
• at the start of and during flowering: spraying with oidium treatment agent every 7 to 10 days, with the addition of net sulphur if necessary
• at the end of flowering (usually July/August): careful foliage work and spraying of Oidium treatment with added net sulphur (guideline 2-3 kg/ha)
• from mid-August, no more use of net sulphur, as this can later impair the flavour of the wine(bruising)

Treatment in case of infestation:

• Washing with 1.5 per cent soft soap solution
• Application of oidium treatment agent with the addition of net sulphur, as described above

Downy mildew (Peronospora)

Symptoms include

• round, 2-3 cm large, light-coloured, oily spots on the upper side of the leaves
• white fungal turf on the underside of the leaf
• white to yellowish fungal turf on flower heads (inflorescences) and young berries

favouring factors:

• prolonged warm and humid weather
• heavy rain (5-10 mm in 2-3 days)
• 4-6 hours of leaf wetness at at least 10 °C over 24 hours

preventive cultivation measures:

• high and wide-ranging training of the vines
• conscientious foliage work
• moderate nitrogen fertilisation

preventive treatment:

• most important treatment period: during flowering
• use peronospora treatment every 7 to 10 days