Biological fungicide, copper has been used for over a century in agriculture: cupric products are a classic of phytosanitary defense, the first uses in crop protection date back to 1882 and since then copper, also called verdigris, has never been abandoned.
Cupric treatments are allowed in organic farming where they are used in stopping the spread of fungal and bacterial diseases in the form of various compounds and formulations. However, not everyone agrees on the fact that a truly organic agriculture resorts to the use of copper and the reason for this mistrust is linked to some risks that the excessive use of copper entails on the environment and the effects it can have on the environment. ground.
For this reason, however, there are limitations to its use and before approaching it it is important to know the products, how they work, how they are used and when. So let’s see in this article which are the best known cupric products and how to use them sparingly and sensibly.
Main copper products
There are many commercial products registered in Italy, but care must be taken: in some of them copper is mixed with other fungicides, making their use prohibited in certified organic farming and however not recommended in non-certified ones that intend to operate in a similar way or in small family gardens that want to obtain natural vegetables. Below is an overview of possible copper-based biological fungicide treatments currently in use in agriculture.
The Bordeaux mixture
Bordeaux mixture is a historical copper product that takes its name from the French city where it was first tested. Contains copper sulphate and calcium hydroxide in a ratio of approximately 1: 0.7-0.8, and has a clearly visible blue color on the treated vegetation. The proportions between copper sulphate and calcium hydroxide can also shift: if the copper sulphate is increased, the mash becomes more acidic and has a quicker but less lasting effect, while with a more alkaline mash, i.e. containing a greater dose of calcium hydroxide, the opposite effect is obtained, i.e. less prompt but more persistent. To avoid unpleasant phytotoxic effects, it is still recommended to use a neutral reaction slurry, given the proportions indicated above, and which is usually the one found in commercial preparations already mixed and ready for use.
There are 2 copper oxychlorides: copper and calcium oxychloride and tetraramic oxychloride. The latter has a copper metal content ranging between 16 and 50% and its action is generally more prompt. The first contains from 24 to 56% of copper metal and is more effective and more persistent than tetraramic oxychloride. However, both are the best cupric products to use against bacteria.
It has a copper metal content equal to 50%, and is characterized by a good promptness of action, and an equally good persistence. In fact it is composed of needle-like particles that adhere well to the treated vegetation, but for the same reason present the risk of phytotoxicity.
Tribasic copper sulphate
It is a very soluble product in water, has a low copper metal content (25%) but is quite phytotoxic on plants so you have to be careful with the doses and methods of use.
Mode of action of copper
The anticryptogamic activity of copper derives from cupric ions, which released in the water and in the presence of carbon dioxide, cause a toxic effect on the spores of pathogenic fungi, starting from their cell walls. The spores are in fact blocked in their germination.
Copper does not penetrate into the plant tissues and in fact in the technical jargon it is said that it is not a “systemic” product but a covering and it really works only on the plant parts covered by the treatment. As the leaf surface expands as it grows and the shoots develop, these new plant portions are then discovered by the treatment and possibly exposed to pathogenic attacks.
This is one of the reasons why more treatments are performed in professional crops during the growing season, especially after prolonged rain which creates the basic conditions for the onset of the disease.
When to use copper
Copper is used during the growing season on the affected green parts of fruit trees, vines, olive trees and vegetables. In the orchard and in the vineyard it can also be used at the fall of the leaves to eradicate the wintering forms of corineo, monilia, downy mildew of the vine and other common fungi.
The adversities from which it protects
With the exception of powdery mildew, copper-based products are potentially usable against various pathogens, covering most of the diseases of the garden and the diseases of the orchard: vine and horticultural downy mildew, bacteriosis, septoria, rust, alternariasis and seekers of horticultural plants, cycloconio of the olive tree, blight of pome fruit and others.
Which crops are treated with copper
On organically grown vines it is considered indispensable against downy mildew, while in the vegetable garden it prevents downy mildew of potatoes and tomatoes and diseases affecting other species. In the orchard, copper can be replaced in various cases, for example against peach blisters or apple scabs and, however, calcium polysulphide can be preferred, but it is still widely used against these and various other pathologies such as corineum. Copper can also be used against various ornamental plants suffering from pathologies, such as rose scab.
How to use it: methods and dosages
The cupric products are used diluted in water and scrupulously respecting the doses and indications given on the labels of the commercial packages purchased.
The treatment is nebulized with a sprayer pump or backpack atomizer.
As an example, if on the package it is indicated to use 800-1200 grams of product for each hectolitre of water, it is calculated that to treat one hectare approximately 1000 liters of water are needed, or 10 hectoliters with 8-12 kg of product. This does not mean that we are exceeding the doses of 4 kg of copper / ha / year with a single treatment (maximum limit allowed in organic farming), because what matters is the actual copper content. If the copper metal content is 20%, with 10 kg of product we distribute 2 kg of copper metal and this means that at most we will be able to do 2 treatments of this type throughout the year. For a small vegetable garden or orchard the calculation is the same and only the proportions change (eg: 80-120 grams of product / 10 liters of water).
Toxicity and harm to the environment
Copper is actually not a harmless product and you need to be aware of the effects it can cause in the agroecosystem. On plants, copper can cause phytotoxic effects, in some cases giving the symptoms of iron chlorosis (yellowing) or burning and russeting on the peel of pears and apples.
Copper does not undergo degradation and from the vegetation it falls to the ground with the rain that washed it away, and once in the soil it is poorly degradable, it binds to clays and organic matter, often forming insoluble compounds. After repeated treatments, copper tends to accumulate, causing a negative effect on earthworms and various other soil microorganisms. For this reason, certified organic farms had to comply with the limit on the use of 6 kg / ha per year of copper metal, a limit which, however, from 1 January 2019 goes to 4 kg / ha / year for everyone.
In the orchard it is essential to avoid treatments during flowering, due to their negative impact on bees and other beneficial insects, on which copper has a certain toxicity.
In addition, we must also consider the shortage time, or the time that must elapse between the last treatment and the collection of the products, which is 20 days and takes away the convenience of using it for short-cycle or frequent-harvest crops. Fortunately, lighter products with shorter lead times have also been released to the market.
Alternatives to copper
An objective of research in organic farming is to identify more and more alternatives in order to reduce the amount of copper metal in soils. For “copper metal” we mean the actual quantity of copper, given that a product also contains other substances in different%.
There are several alternatives to copper with less impacting effects on the environment, but they must be used very promptly and with an approach based on prevention.
For example, preventive treatments can be made with macerates or decoctions of horsetail, which stimulate the natural defenses of plants, and on the vine it seems that even willow teas have preventive effects against downy mildew. To these products are also added the essential oils of garlic and fennel and that of lemon and grapefruit, both of which have an interesting anticryptogamic function. These products are particularly dear to biodynamic agriculture, but even “normal” organic farmers could try them and / or intensify their uses and even more so it is recommended to do so for those who grow for self-consumption.
We also mention the zeolites, rock powders with which treatments are carried out with certain fungicidal and anti-insect effects.
In short, copper is not the only solution to all plant diseases and it is good to use it sparingly and trying other ways.
The legislation on the use of copper in organic farming
Copper-based products appear in the list of permitted pesticides and plant protection products of Annex II of Reg CE 889/08, which contains the application methods of Reg CE 834/07, the reference text on organic farming valid throughout the EU.
From 2021, the new European regulations on organic farming will be the EU Reg. 2018/848 and the EU Reg. 2018/1584, texts already out but not yet in force. Annex II of EU Reg. 2018/1584 also shows the possibility of using copper, as in the previous one: “Copper compounds in the form of copper hydroxide, copper oxychloride, copper oxide, Bordeaux mixture and copper sulphate tribasico ”, and also in this case, in the next column, it is sanctioned:“ Maximum 6 kg of copper per hectare per year. For perennial crops, by way of derogation from the previous paragraph, Member States may authorize the exceeding, in a given year, of the maximum limit of 6 kg of copper provided that the average quantity actually applied over the five years constituted by the year considered and from the previous four years does not exceed 6 kg “.
However, on December 13, 2018, the 1981 EU Regulation came out, which concerns the use of copper-based compounds in agriculture (not just organic). As an important novelty, it has been defined that copper is a “candidate substance for substitution”, that is, it is expected that in the future it will no longer be authorized for agricultural use. In addition, the limit of use is set at 28 kg / ha in seven years, or an average of 4 kg / ha / year: an even greater restriction that affects all agriculture and even more so organic. This change will take effect from January 1, 2019.
A holistic view
However, European legislation makes it clear that the products listed in the annexes should be used only if and when necessary, and first of all work on prevention and compliance with the basic principles: rotations, care for biodiversity, choice of resistant varieties, use of green manures, correct irrigation and much more, or the adoption of good practices that make an agricultural context, small or large, resilient and less dependent on external inputs.
Even in a vegetable garden or in a private orchard, good practices can be applied such as: drip irrigation to reduce the likelihood of the plants becoming ill, choice of ancient fruit trees more resistant to diseases, use of macerates and inter-associations between vegetables. By respecting all these precautions, the probability of having to use verdigris is significantly reduced.
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