Not all potato diseases are cured. And the first on this list will be the black leg. We will talk about how to identify the disease and protect the crop from infection.
Black leg is a lesion of the hypocotal knee near the root collar. The most striking sign is considered the blackening of the lower part of the stem of a potato bush - hence the name of the disease.
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Causes
The disease is caused by bacteria of the species Erwinia carotovora. They are active in temperatures ranging from + 2 ° C to + 27 ° C, subject to high humidity. Reproduction is facilitated by soil acidification, an excess of nitrogen and a lack of potassium. Bacteria cannot hibernate in the soil, so they temporarily settle in plant debris and tubers.
Potatoes, which are grown on heavy, clayey and sandy loam soils in areas with a humid climate, are at particular risk.
The source of infection becomes:
- infected planting material;
- weeds;
- decaying plant remains.
The disease is transmitted from infected bushes or tubers to healthy ones:
- by contact (contact of plants or tubers);
- carried by insects (nematodes, wireworms, earthworms, cicadas, aphids, Colorado beetles);
- with water droplets during rain or watering.
Symptoms
In dry weather, the disease develops slowly, and signs of plant infection are poorly expressed (small leaves, growth retardation). Later it manifests itself in the form of wilting of bushes, decay of stems and tubers.
Heat and dampness provoke an active course of the disease with vivid symptoms:
- The upper leaves grow at an acute angle, while the lower leaves curl into a boat. The bush gradually turns yellow, wilts and dries.
- The stems soften at the base and change color to yellow, brown, dark green, black. Then they lose their stability and fall. Shoots break off easily. The effect of "floating stem" is observed - the tops decompose into mucus of a dark green color.
- Roots rot. They become soft, slippery, watery.
- Stolons decompose - a rotten cavity forms in the places of attachment with the tuber. The tubers darken. In the region of the eyes, brown necrotic spots are noticeable. A wine smell appears and later - putrid.
Control measures
The disease cannot be cured. There are no varieties with immunity either - only with varying degrees of resistance. Identifying a black leg at an early stage of development is problematic. In cases of weak infection, the diseased areas are cut off and the bush is treated with Fundazol. If the moment is missed and there are many signs of damage, the plant is dug up and burned. The soil is disinfected with a solution of copper sulfate.
Agrotechnical preventive measures:
- Competent crop rotation. Planting material is renewed every three years.
- Cleaning of vegetable debris.
- Control over soil acidity.
- Weed cleaning.
- Bulkhead tubers before planting.
- Selection of relatively resistant varieties.
Chemical
- treatment of tubers with any fungicide of the phenylpyrrole class (before storage and before planting);
- before and after flowering, the bushes are sprayed with a solution of biofungicide ("Kazumin", or "Effect").
A favorable environment for the causative agent of the black leg is an excess of moisture and heat. The disease can also be provoked by mistakes in agricultural technology. It is difficult to diagnose it at an early stage, and it is useless to treat plants with a strong infection. Therefore, the main emphasis in the fight against the disease is placed on prevention.
Have you met such a disease on potatoes as black leg? Do you know how to deal with it?
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