Widely used in cooking, animal nutrition and medicine for its aromatic and therapeutic properties, the onion cannot miss in a garden. The different layers that characterize the bulb of this biennial herbaceous species, grown as an annual, of the Liliaceae family are not enough to protect the plant from pathogenic agents ( virus , bacteria Yes mushrooms ). If you choose to grow organic onions, you must learn to recognize and combat adversities, but above all to prevent them with proper care.
Onions can be attacked by mosaic or yellow mosaic viruses and bacteria which cause three types of rot (soft, sulfurous and sour) during harvesting and storage. There are several fungi caused by fungi during cultivation which, together with pest attacks, negatively affect the productivity of horticultural species. Peronospora, botrytis, alternaria and charcoal rot occur in the aerial part of the onion, while Fusarium wilt, anthracnose, pink root rot and charcoal rot occur in the hypogeal part.
We will find out about the three most common fungal diseases of this culture, which can be defended against attack by natural methods.
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onion burn
Although it looks like a mushroom, the mildew ( Downy mildew of the Schleidenes ) belongs to the Protista family of downy mildew. When attacking onions, the oomycetes give rise to elongated, whitish spots on the leaves which turn into purple-grey mold in high relative humidity, while low humidity tends to necrosis. Affected leaves turn yellow and curl downward, showing to rot while the bulbs are small and generate stunted seedlings.
As late blight needs water to thrive, it is essential to avoid water stagnation by draining excess water and doing a good tillage in the garden. Other useful practices to prevent the disease are the use of resistant bulbs or cultivars, crop rotation and the destruction of plant debris likely to be infected. In addition, when fertilizing the onion, attention should be paid to the supply of nitrogen, which should not be excessive. To combat the pathogen, it is also possible to use horsetail or dandelion plants and, when strictly necessary, to use copper products.
The preparation of the equisetum ( Equisetum arvense ) is a decoction of the leaves and stems of the plant, which grows spontaneously in moist soil. The decoction is applied to onion leaves once every 15 days and has an anticryptogamic action that strengthens the crop against mildew. Filtered and diluted 1:10, the preparation can also be used as a foliar or root fertilizer and can be mixed with nettle. dandelion preparation ( Taraxacum officinale ) is a whole plant undecotto that increases the onion’s resistance to disease.
copper products the most used against mildew are copper oxychlorides and Bordeaux pulp . Tetraramic oxychloride is an immediate-acting substance, while copper calcium oxychloride is more effective, but also more persistent than tetraramic. Bordeaux pulp has a variable activity depending on the ratio between copper sulphate and lime. Treatments with copper-based products are necessary when climatic conditions are particularly favorable to the development of mildew and are carried out during the coolest hours. The biological agriculture uses copper to 4 kg per hectare and per year, since the metal does not degrade and accumulates in the soil in the form of insoluble compounds with negative effects on microfauna and microflora.
botrytized onion
The botrytized onion ( Botrytis squamosa , Botrytis allii ) belongs to the Sclerotiniaceae family. B. scaly attacks young leaf tissue onion causing infections over the entire surface of the leaf, while B. allii enters the neck through damaged tissue infecting the bulb . Affected leaves show small pale spots and die prematurely. For their part, the attached bulbs turn brown, soft and fluffy. A greyish-white micellar growth it pierces the scales of the bulbs and small black sclerotia develop on the outer scales.
To avoid botrytis attacks, the onion should be grown in a different area from where it was grown the previous year, alternating . In addition, it must be planted avoiding damaging the collar and placing it at such a density that it favors the circulation of air between the plants and therefore the drying of the leaves. To avoid wetting the leaves, it is preferable to limit irrigations and to carry them out in the morning. If you water in the evening, try not to wet the plants but only the soil.
Botrytis spreads rapidly in moderate temperatures (10-24°C) and high humidity. When climatic conditions are conducive to the development of the fungus, it is advisable to begin operations as soon as the first symptoms appear on the onion and to repeat them every 7 to 10 days (every 15 days if products based on copper are used in the absence of rain). Among the substances that can be used for the defense against botrytis, we recommend Sodium bicarbonate mixed with water and dispensed with a shoulder pump.
sauté onions
Also the Fusarioum ( Fusarium oxysporum FSP cepae), a fungus of the Nectriaceae family, can attack onions, especially when temperatures reach 25-32°C. Ascomycetes penetrate vascular tissues weakening the plant of the basal leaves and causing stem browning, chlorosis, stunting, wilting Yes drying of the harvest.
For to prevent Fusarium attack, you can intervene in different ways. For a lado, the rotation of cultivos impide that the cebolla is cultivated in el mismo suelo unos años más tarde, is that el hongo can survive during mucho tiempo in a suelo ya contaminated y, por lo tanto, atacar a la specie incluso después de much of the time. On the other hand, rotations with grasses and legumes, the supply of organic matter, the use of tolerant varieties and healthy propagation material, localized irrigation and soil drainage play a fundamental role in the prevention of the fusarium.