Copper is a fungicide and bactericide which is distributed on plants, it is not absorbed by plant tissues, but is deposited on the external parts of leaves and other epigeal organs. To date, many of the actions against both fungal and bacterial parasites are based on the use of cupric products. The copper enters the phytosanitary defense of the olive tree against cryptogams such aspeacock eye, the leprosy of the olives, the plumbing, smoke, rameal cancers , mange of the olive tree.
In addition to influencing pathogens, the action of copper also takes place on the epidermal plant tissues, hardening them. This leads to further limited resistance to pathogens. Starting from 1 January 2019, EU Regulation 1981/2018 limited the amount of copper that can be used on crops to a dose of 28 kg/ha of copper in 7 years.
Action of copper and its preventive operation
Although it is not yet well known how the copper ion manages to block fungal parasites, it is thought that this modifies the composition of the proteins and enzymes that form the cell membranes of fungi and bacteria, compromising their integrity and ability to be selective , so much so that they are no longer able to block the passage of the copper ion itself, which manages to filter inside the cell. Once the cell membrane has been passed, the copper ion alters the respiratory processes and slows down the reproduction of the affected cell, leading to its death. The fungicidal action of copper is mainly directed against fungal spores, released into the environment or during germination, it acts by slowing down their germination, it acts little or nothing against the mycelium which has already penetrated the plant tissues. Due to its contact mode of action, the application of copper must take place before the spread of the disease, therefore it is to be considered as a preventive plant protection product.
In olive trees, copper induces a selective fall of the diseased leaves: in this way it decreases the amount of inoculum of fungal spores. When diseased olive trees are sprayed with cupric products, a selective defoliating effect could occur. Given the preventive and protective nature of copper, the moment of application is decisive.
Given the high toxicity of the copper ion, it is rare to encounter fungal strains resistant to copper products.
Cupric products
Among the copper products we find:
1) Copper sulphate in two forms:
I. Pure copper sulphate, which is very fast acting but is quite phytotoxic.
II. Neutralized copper sulphate in the two compounds:
a) Bordeaux mixture, sulphate mixed with slaked lime, made up of a complex of copper salts: it has good resistance to washout, promotes thickening of the leaf cuticle and fruit epidermis, controls vegetative luxuriance, is very persistent; on the market there are various forms depending on the percentage of copper metal contained;
b) tribasic sulphate: in this formulation the neutralization is obtained with a manufacturing process different from that of the Bordeaux mixture. It is very soluble in water, its pH tending towards acid gives it greater aggressiveness and promptness of action, it is always produced starting from an aqueous solution of copper sulphate which is neutralized by ammonium hydroxide.
2) Oxychlorides
The oxychlorides, compared to the Bordeaux mixture, are less persistent, but have a more immediate cryptogamic action and less accentuated phytotoxicity than copper hydroxide. There are various forms on the market, depending on the percentage of copper metal contained, the most used concentration is 50% copper metal. They are divided into:
a) copper and calcium oxychloride or triramic: has a prompt action, efficiency and persistence, but has a slower biological action. It represents the most active form against bacteriosis, as a copper ion it acts on cryptogams by leaf contact, penetrating the spores and conidia and preventing their germination. Copper oxychloride is produced starting from a copper chloride solution which, through a process of oxidation and hydrolysis, allows to obtain the desired salt.
b) tetraramic oxychloride: it has a less rapid action than triramic, but more persistent; the final release of copper is greater than that of triramic oxychloride.
3) Cuprous oxide
Cuprous oxide is slightly phytotoxic and has good adhesion to the treated vegetation. The high specific weight tends to make the product precipitate, so the suspension in water is strongly limited in time. It is produced through an electrolysis process, or through redox of copper oxide.
4) Copper hydroxide
Copper hydroxide has prompt action, but is slightly phytotoxic: to avoid treatments during flowering, it is obtained starting from an aqueous solution of cupric sulphate to which excess ammonium hydroxide is added and, subsequently, an aqueous solution of sodium hydroxide.
The copper-based compounds can be found in solid or liquid formulations, the former are called formulations in water-dispersible granules (WG), characterized by micro-granules which, once introduced into the water, disintegrate and disperse the copper compound in the water. The liquid formulations, in concentrated suspensions (SC), are instead stable, given by a cupric compound which, for use, is diluted in water.
Ratings
The effectiveness of copper is proportional to the quantity administered, among the various commercial formulations. We find it as wettable powder, dispersible granules, suspension. The most popular is as hydroxide, because it has a greater capacity to release active copper even in limited dosages, which go down to 100 grams per hectolitre of metal. The traditional copper sulphate and the classic Bordeaux mixture are the cheapest solutions, even if for the sulphate as it is it should be kept in mind that, due to its recognized superior effectiveness, it gives more risks of phytotoxicity and is easily washed away.
New products with the presence of penetrating cupric products
In recent years, formulations have been introduced where copper has a low concentration, generally as sulphate and in combination with substances such as amino acids, of animal or vegetable origin, or synthetic substances, capable of giving it the ability to penetrate into the tissues vegetables.
With these systems copper, in addition to carrying out a surface activity, penetrates inside the tissues, also carrying out an action of obstacle to fungal and bacterial parasites. It should be considered that in these cases we are not dealing with plant protection products, but with fertilizers and corroborants, among these we find:
1) copper peptidate: the copper ion, at 5%, is combined with proteins which help it to penetrate inside the leaf. However, this union of proteins and copper can give phytotoxic phenomena, especially in particularly cold or hot and humid or rainy seasons.
2) copper tallate: it is prepared with resins, fatty acids extracted from pine wood and copper hydroxide, the mechanism of action and its effectiveness are not yet well known, however it is known that it has low phytotoxicity.
3) copper gluconate: it is a salt of gluconic acid, composed of gluconic acid dihydrate in the crystalline state with 8% of pulverized copper sulphate, the copper is transported inside the leaves without presenting phytotoxic phenomena, it is remarkably easy to move from the upper page to the lower one of the leaf, therefore it has a fast translaminar action.
AIPO Director
Interregional Association
Olive producers
