Or downy mildew of cabbage. The pathogenic fungus infects cabbage, radishes, turnips, turnips, turnips, watercress, and some weeds, especially a shepherd’s bag, at any age, but is most dangerous for young plants. This disease develops mainly on the leaves: first, chlorotic spots appear on the upper side, then they turn into light yellow, angular, oily spots, which subsequently turn brown.
On the underside of the leaf, in places of spots, a grayish-purple plaque from sporulation organ forms. The spots gradually increase, merge, and the leaf dries out. With a severe defeat on the plant, only one petiole remains green.
Heavily affected leaves die prematurely, which can lead to the complete death of seedlings. The disease spreads especially rapidly in rainy weather, and in greenhouses – at a temperature of + 18–23 ° C and at high relative humidity. The mushroom hibernates in the form of spores on fallen leaves.
For seed disinfection, first of all, it is necessary to warm them up in hot water (at a temperature of + 48–50 ° C) for 15–20 minutes. Immediately after warming up, the seeds should be immersed in cold water for 3 minutes and then dried. When growing seedlings, greenhouses, greenhouses and film shelters are recommended to be systematically aired. When the first signs of cabbage oversporosis appear, the seedlings should be sprayed with copper chloride (0.4% suspension or 40 g per 10 l of water) or Bordeaux liquid (100 g of copper sulphate and 100 g of lime in 10 l of water) and top dressing with ammonium nitrate before landing in the ground. We must try to avoid sharp fluctuations in temperature and high humidity in the structures of the protected ground.
Relatively disease-resistant varieties should be grown. All post-harvest residues should be removed and incinerated.