What is the point necrosis? This is a functional non-infectious disease, manifested in the form of many small slightly depressed lead-gray or black spots up to 3 mm in size, which has a different shape – from round to elongated-angular. The disease is point necrosis most often manifests itself on the external leaves of the head of cabbage, but sometimes it can also occur on the internal leaves. In any case, the heads of cabbage lose their presentation. Typically, the intensity of the development of point necrosis increases in the second half of the storage period, due to which there are large losses of production.
The main cause of point necrosis is a violation of the conditions for growing and storing cabbage.
Excessive doses of nitrogen fertilizers contribute to the appearance and development of the disease, due to which there is an uneven physiological maturation of covering and parenchymal leaf tissues, which in turn leads to focal (point) functional necrosis. At these “unripe points”, as a rule, subsequently there is a secondary defeat of various infectious principles (imperfect fungi from the genera Botrytis, Cladosporium, Alternaria, Macrosporium, etc.).
It is thanks to this that the color of the spots changes from light gray tones to dark brown and black.
The use of increased doses of potassium and phosphorus (while nitrogen is introduced only at the physiological minimum), the introduction of boron and molybdenum, liming of acidic soils – all these measures significantly reduce the likelihood of this disease and its harmfulness.
It should also be borne in mind that point necrosis can be widespread during storage and if cabbage is at a temperature of 1–4 ° C for a long time.