**4. Copper in agricultural use: Sustainable horticulture**

First records of the agricultural use of Cu compounds date back to 1761, when the discovery of the antibacterial effects of copper sulphate preparations used on seed grains set up further standards in cultivation practices for the following decades.

The most important breakthrough of copper use in viticulture though was undoubtedly in 1880, when the French scientist Pierre-Marie Alexis Millardet from the Bordeaux district in France chanced to notice that those vines, which had been daubed with a paste of copper sulphate and lime in water, in order to make the grapes unattractive to passers-bys and as well as animals, appeared less affected by downy mildew. Only five years later in 1885 Millardet announced his discovery to the world, a cure for the dreaded mildew through the application of the mixture of copper sulphate, lime and water, up to the present day called the Bordeaux mixture. Additionally to the Bordeaux mixture, but including copper sulphate and sodium carbonate (soda crystals) the so called Burgundy mixture appeared few years later.

At that time the Bordeaux and Burgundy mixtures became indispensable fungicides against various fungus diseases of plants, where the prevention enhanced with the proper application, means an appropriate timing and correct use of the fungicide. Consequently, as standing for a successful plant protection method up to the present days, many thousands of tons of copper are used annually in agriculture all over the globe.

The days of prosperity of the production of fungicides based on copper compounds were in the middle of 20th century when many different chemical combinations with copper were applied. In the last decades and these days pharmaceutical corporations have been fabricating copper based fungicides in soluble forms of sulphates, oxychlorides, acetates, carbonates, oleates, silicates, ohydroxides etc. Most compounds of copper adopt the oxidation states Cu+ and Cu2+, respectively called cuprous and cupric. Their efficiency against fungal and bacterial infections is mostly reflected in their capability to retain on the plant surface, but not by the number of applications or the concentration of the agens in the fungicide. Copper is also biostatic which means that bacteria cannot grow on surfaces treated with it. Copper barriers can range from copper tape made as a slug barrier to more decorative hammered copper sheeting. Any copper that leaches into the soil around the plants is non-toxic and will not adversely affect the plants or people consuming the vegetables and fruits.

Copper in Horticulture 265

copper as metal, therefore the content of Cu in 1 % Bordeaux mixture varies between 0 and 25 %. On the other hand 1 % Burgundy mixture is made by dissolving 1 kg of copper sulphate in 50 litres of water and separately 125 kg washing soda (or 0.475 kg soda ash) in 50 litres of water. After that the soda solution has to be slowly added to the copper sulphate solution with stirring. Both mixtures have been effective in controlling most of the fungi diseases of plants, applied in a time span of 10 to 20 days, depending on fungi species, plant, weather conditions, age and phenological stage of plants etc. According to the manner of Cu use it is important that first spraying is done before the diseases is expected and continued at regular intervals throughout the susceptible period. The protective coating of Cu mixtures prevents spores germination and consequently their damages caused by penetration through tissues of unprotected parts of plants. An effective spraying scheme has to ensure permanent copper coating over susceptible plant parts, what demands accuracy of the timing of the spraying,

especially at precipitation (> 30 mm) and at intensive fruit growing (fruit enlargement).

Leaf curl (*Taphrina deformans*) Rust (*Puccinia pruni-spinosae*)

Bitter rot (*Glomerella cingulata*) Black rot (*Physalospora obtusa*) Blossom wilt (*Sclerotinia laxa*) Blotch (*Phyllosticta solitaria*) Canker (*Nectria galligena*) Fireblight (*Erwinia amylovora*) Pink disease (*Corticium salmonicolor*)

Scab (*Venturia inaequalis*)

Rust (*Puccinia pruni-spinosae*)

Shot hole (*Clasterosporium carpophilum*)

Bacterial rot (*Pseudomonas syringae*) Fruit spot (*Cercospora purpurea*) Scab (*Sphaceloma perseae*)

Fruit rot (*Sclerotinia vaccinii-corymbosi*) Leaf rust (*Pucciniastrum myrtilli*)

Anthracnose (Black spot) (*Glomerella cingulata*)

Black rot (Die back) (*Botryodiplodia theobromae*) Helminthosporiosis (*Helminthosporium* sp.)

Sigatoka disease (Leaf spot) (*Mycosphaerella musicola*)

Powdery mildew (*Microsphaera alni* var. *vaccinii*)

Shot hole (*Clasterosporium carpophilum*)

Blossom wilt (*Sclerotinia laxa; Sclerotinia fructigena*)

Blossom wilt (*Sclerotinia laxa and Sclerotinia fructigena*)

**Plant Disease and Pathogen** 

**Blackberry** Cane spot (*Elsinoe veneta*)

**Fruits**

**Almond**

**Apple**

**Apricot**

**Avocado**

**Banana** 

**Blueberry**

Copper plays an important role not only in pathogen controlling but also in soil fertilization, animal nutrition etc. Excessively long copper use in plant protection but also in terms of fertilisation in modern agriculture lead to copper accumulation in soils, where copper surplus is considered if the soils contain more than two parts per million available copper, bearing in mind the physiological and biochemical needs of the plants. On the other hand the same soil conditions in context of copper deficiency can also affect nutritional statuses of animals and consequently their life expectancy.
