What is allelopathy?

Allelopathy is the ability of some plants to influence others through a biological phenomenon that produces biochemical compounds called allelochemicals. These compounds establish symbiotic or antagonistic relationships between plants of the same crop. They can produce positive effects (positive allelopathy) or negative effects (negative allelopathy) on the organisms in which they intervene.

For these fundamental reasons, synthetic chemical products are not used in the control of pests, chemical products that are used by conventional horticultural farms and that so indiscriminately kill pests, diseases and other living beings found in the fumigated area, with the consequent alteration of the natural conditions of the environment.

This, together with the toxicity load left by these synthetic pesticides on the plant, makes us seriously consider what we consume and, in our particular case, how we cultivate our orchard or urban orchard. An alternative to all this is the application of allelopathic controls, highly effective when it comes to obtaining a good result in the control of plagues and diseases of our crops and totally sustainable with the environment.

Plants with allelopathic properties release or exude through their roots, leaves or flowers fragrances and essences containing the above allelochemical compounds. Allelopathic substances can have attractive, repellent, inhibiting or stimulating effects on other plants, insects or microorganisms such as fungi or bacteria. Plants with allelopathic properties can be vegetables, aromatic herbs, medicinal plants and some weeds.

Accompanying plants

Plants called companions or relatives provide a mutual benefit with other plants. This positive association can influence from the germination of the seeds, growth and development of the plant, until in the flavour and final aroma of the obtained vegetables. For example, nettle sown near aromatic plants increases their aromatic quality. Accompanying plants should be sown with the rest of the crop so that the fumes are absorbed from one plant to another.

Table of different types of crops with some of their companion or related plants.

Repellent plants

Repellent plants are plants with a strong aroma that serve to keep insects away from the main crop. Some plants repel a specific insect and others can protect against different pests. They can be sown between the crop, protecting some concrete plants, or bordering the orchard making of protective barrier, covering its effect an area that can get to be of 10 meters of distance.

Trap Crops

Trap crops are plants chosen to attract harmful insects and keep them away from the main crop. These plants are planted in the perimeter of the crop to be protected away from the harmful insects, or interspersed between the rest of the plants to concentrate pests and be able to trap and eliminate them. Another way to use trap plants is to help reproduce parasites or predators of the pests that attack the orchard.

Decoctions and slurry

A more traditional way to take advantage of the allelopathic properties of the plants is by means of aqueous fermentation or decoction of these plants, obtaining preparations as resolute as the nettle slurry, which goes so well to give vigour and health to the plants and to prevent and eliminate diseases or the decoction of horsetail, also perfect for the prevention of fungi and to weaken plagues. Both preparations can be used directly in irrigation and sprayed on the crop for foliar absorption.

Nettle slurry

The benefits of using nettle slurry as both a fertilizer and insecticide in our garden are many. It provides nitrogen, minerals and microelements such as iron, phosphorus, magnesium, potassium, calcium and trace elements. Used directly in irrigation, it activates compost and fortifies and activates the soil’s microbial flora, strengthens the plants’ defences and stimulates their growth. Sprayed in addition to fertilizing the plant foliar fights diseases such as mildew and powdery mildew and repels insects, especially aphids and some mites.

Preparation of nettle slurry

We will need 1kg of fresh nettle, or 200gr if it is dry, for every 10 litres of water, if the water is from rain or from a much better source or well; we should also look for a plastic container, taller than wide. The container should not be red or yellow, these dyes have chromium and would be transmitted to the slurry, nor transparent to prevent light from entering.

We will place the container in a place where the sun does not touch it directly and we will cut the nettle to put it together with the water inside the drum. Submerge the nettle by placing a weight on it, such as that of a stone. We will place a lid that is not watertight, it is only so that insects or other things do not fall inside, it is an aerobic fermentation, therefore the slurry has to be aired. Some do not cover the first 4-5 days to air better, what is essential is to remove it 2 times a day always leaving the nettle at the end submerged again.

After 5 days it will begin to bubble and foam and give off a rather unpleasant smell, for this annoying consequence, conveniently, the drum in addition to being in the shade is also removed. At an ambient temperature between 20-22 degrees the fermentation will last between 10 and 15 days approximately, if there is more temperature the fermentation will be faster, on the contrary, if it is lower the fermentation can be extended up to one month.

We will know that the process has finished because the foam that we have observed that was made days ago will have disappeared, it will only be strained well and pack it trying that there is no air left, this way we will avoid a second fermentation that would spoil the product. If we have not done this last step well, we will notice that the container inflates. Store in a cool, dark place.

Application of nettle slurry

The application, if it is direct to the irrigation, must be diluted a 20% in water, 1 litre of the extract by 4 litres of water. If we are going to apply it pulverized on the plant, the dissolution in water should be 10%, 1 litre of extract for 9 litres of water. The foliar application should be made when there is natural light because we need the plant in photosynthetic activity and with the stomata open, always in the morning before the sun is high or also before sunset.

For a good preventive effect on the crop apply every 10-15 days.

Decoction of ponytail

The extract obtained from horsetail decoction is an excellent ecological fungicide, applied with spray on the plant for foliar absorption prevents fungal diseases such as rust, coccidiosis, mildew, septoria, etc.. It has a high silica and sulphur content, and the presence of equisetonine, a toxic saponin for fungi, makes the cell walls of the plant increase and strengthen, preventing the entry of fungi. As an insecticide, it repels insects such as aphids and red spiders. It is a good growth promoter and can be mixed or interspersed in its application with nettle slurry.

Horsetail decoction preparation

As it is a decoction we will need a pot were to boil the prepared one, better to do it with a dry ponytail that will not need a container of great volume. Put in the pot 50 grams of dried ponytail per 5 litres of water, in the fire with the container covered bring it to the boil and boil for about 30-40 minutes. Without uncovering we will extinguish the fire and we will leave it all night so that it infuses. In the morning we will strain and store the bottled product without air, and we will store it in a place out of the light and fresh. Its full-time effectiveness as a mushroom control is two months, then the extract loss properties.

Application of horsetail decoction

Dilute the extract to 20%, 1 litre of horsetail decoction by 4 of water, spray on the leaves and under them, some mushrooms refuse direct light and are installed on the bottom of the leaves. As a preventive method apply every 10-15 days, in rainy season every week. As a healing method, when the fungus is already lodged in the plant, apply three days in a week.

The use of allelopathy to control pests and diseases in plants is beneficial in every sense, ensures a quality crop and sustainable in the long term, gives liveliness and diversity to our garden, specializes us and makes us penetrate more deeply into the fascinating world of organic horticulture, and gives us a little more perspective on the knowledge of the natural balance of the Earth.

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