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Over a century and a half ago copper was already used in organic farming and still products with this base are the best remedies on several occasions when you want avoid the use of chemicals but at the same time you can't sit idle. They are products for phytosanitary defense, one of the first, among other things still in use, is verdigris. There are different opinions on the use of copper in organic farming because in fact when we use too much copper, we can risk damaging the environment and the quality of the soil
To date, however, these are accepted products and are often recommended to intervene in the case of fungal and bacterial diseases. Given the distrust of many, they have been called gods usage limits and, before using them for our garden, vegetable garden or field it is very important to study the product we are interested in specifically to understand how, when and how much to use it.
Copper in organic farming: how it works
Why copper to take care of our plants? Due to the presence of cupric ions which become toxic to the spores of pathogenic fungi when they come into contact with water and then with the'carbon dioxide. They act on the cell walls and they do stop germination. Copper-based products are not systemic, unlike many others and this clarification is very important. In fact, it means that copper does not enter the plant tissues, it acts only on the parts that we cover with it and "does not enter the circulation". Excellent because they do not contaminate the plant by filling it with copper but from the other point of view it affects us renew the treatment as the plant grows and new leaves appear that are possibly not protected from pathogenic attacks. To minimize the repetition of treatments it is often used during the growing season, immediately after it has rained a lot. Copper is therefore used in this period, passing products based on this element on the green surfaces of sick trees, on olive trees and on vines. They are also used in vegetable gardens.
A second treatment can also be done during the year, when the leaves fall, both for fruit trees and vineyards, a very useful choice for combating wintering forms of corineo, monilia, downy mildew of the vine and other common mushrooms.
Copper in organic farming: what is it for
Downy mildew of grapevines and vegetables, bacteriosis, septoria, rusts, alternariosis and cercosporiosis of horticultural plants, cycloconio of the olive tree, blight of pome fruit and others. There are many plant diseases that these products can cure, the only one that goes excluded from the list in its entirety and powdery mildew. Fruit trees can be treated with these substances which for some in particular represent a real salvation. For example, when diseases such as peach blister or apple and pear scab occur, calcium polysulphide can be a very valid remedy. Even organically grown vines can be treated with copper, for example when they contract downy mildew which can also affect some plants in the garden, potatoes and tomatoes, always to be treated with similar remedies.
Copper in organic farming: how to use it
It is very important to know and respect the doses allowed by law and recommended by manufacturers when using copper because, as we explained earlier, we must avoid that this metal is dispersed in the environments and penetrates too much into the ground. Let's look at the labels and we obey because copper, even if allowed in organic farming, is not a harmless product for the environment. The leaves and fruits of the treated trees can be damaged, the former turning yellow and in the latter showing burns or color changes on the skin.
The ground can collect copper which, not undergoing degradation, penetrates it with the rain. It binds with clays and other substances already present and forms compounds which, not being soluble, remain where they are and make the soil less welcoming for plants. To pay the price of their presence are also some inhabitants of the soil like i earthworms and other microorganisms who find their habitat in a certain sense contaminated. From the awareness that copper does its damage but also that it serves and is still the first remedy for some plant diseases, the need arose to identify restrictions on use. From 1 January 2019 this threshold is set at 4 kg / ha / year for all.
Those who use these products normally must also know about particular limitations which must be respected in specific situations. When fruit trees are in bloom, for example, copper should not be used because it disturbs bees and other beneficial insects. Also in the orchard we must keep in mind the harvest times because between the stop of the treatment and the harvest, a minimum period of 20 days must elapse, to avoid that the fruits can be potentially damaged.
Copper in organic farming: products
Let's see some examples of copper-based products that we may happen to use. They are all registered in Italy but when copper is mixed with other chemicals, the product is no longer usable in organic farming if you want it to be certified.
There Bordeaux mixture it is certainly the best known and oldest cupric, it has a bright blue color and there are different versions depending on the proportions applied to the mixture of copper sulphate and calcium hydroxide. To avoid phytotoxic effects, it is better to use a neutral reaction slurry such as that found on the market.
Copper hydroxide contains 50% copper, has an instant and persistent effect, dissolves easily in water but must be used in the correct doses because it takes very little to have phytotoxic effects. Let's move on to copper oxychloride or the two versions that we find on the market: copper and calcium oxychloride and tetraramic oxychloride. They are both very good for fighting bacteria.