Onion diseasessignificantly affect the quality and quantity of the crop. The ignored disease symptoms on the onion can lead to the grating of the entire crop, as well as the stored harvest.Fighting onion diseasesis very difficult. Therefore, in order to prevent losses, it is worth learning how to quickly diagnose onion diseases and learn how to combat them. Here are the 3 most dangerousonion diseases and combating themin allotment gardens.
Onion diseases. From the left: downy mildew, alternariosis, white rot
1. Downy mildew of onion
Downy mildew(Peronospora destructor) is the most dangerous disease of onion. It is common in all growing areas, but is most harmful in areas with a humid climate. The fungus hibernates in onions in a latent form. In the new growing season, it attacks the plant systematically, i.e. from the inside. During the drying period of plants, the spores are transferred with the wind to the neighboring onion crops. The development of downy mildew of onion is favored by the constant moistening of leaves (chives) for several hours at night and rainless and warm weather during the day.
The symptoms of downy mildew of onioncan be observed on leaves and inflorescence shoots (seed onion). Yellowish, rapidly enlarging spots appear on them. Leaves and inflorescence shoots become distorted. Strongly controlled leaves curve to the ground, turn yellow and dry. The diseased plant reacts to these changes by producing massively young leaves.As a result, at the end of the growing season, bulbs with thick, non-drying necks are formed, which are not suitable for storage. With high humidity, a delicate gray-violet coating develops on the surface of the yellow spots. Heavily infested plants do not form bulbs.
Fighting downy mildew of onionis based on prophylaxis. Carried out a careful selection of green onions for planting, removing the bulbs with a thickened neck. I pour the herb horsetail decoction over the plants that are endangered with infestation. When harvesting, we carefully remove all plant residues. When we observe the firstsymptoms of this onion diseasewe remove the diseased plants and spray the rest alternately with the following preparations: Dithane NeoTec 75 WG (20g in 2-10 l of water / 100m²), Ascom 250 SC (8 ml in 7 l of water / 100 m2), Atos 250 SC (8 ml in 7 l of water / 100 m2) or Dobromir Top 250 SC (8 ml in 7 l of water / 100 m2), repeating the treatment every 7-10 days (maximum 4 treatments). Add a few drops of soap to the working liquid to increase its adhesion.It is not recommended to use copper preparations as they delay the development of onions.
2. Onion alternaria
Onion alternaria(Alternaria spp.) Usually occurs as a complication on bulbs previously affected by downy mildew. The disease develops in the second half of summer, in warm (21-32 ° C) and humid weather.
The symptoms of this onion diseaseare dark, brownish-purple spots on the chives that are covered with a velvety mycelium coating. The disease leads to an accelerated leaf dieback. The onion hulls crack and become dark spots. Such onions are not suitable for storage.
The control of onion blightingis carried out in parallel with the control of downy mildew, using the same chemical agents as in the case of downy mildew.
3. White Rot Onion
Onion's white rotis caused by the soil-borne fungus Sclerotium cepivorum.This fungus attacks vegetable and ornamental bulbs. Infection can occur when we grow an onion in a bed of other bulbs. Another source of infection is infested planting material (e.g. spring onion) and plant debris left in the ground. Thisonion disease is especially dangerousin the cultivation of winter onions from autumn sowing.
The symptoms of white onion rotcan be noticed after lifting the plant from the ground. Rotting bulbs show a wadded, white, compact mycelium. Black, hard particles (sclerotia), the size of poppy seeds, are deposited on the mycelium. This is a very important feature that helpsrecognize this onion disease
Combating white rot on oniononce the disease has already appeared on the plants is impossible. Therefore, measures should be taken to limit the appearance of this disease. The most important thing is the correct crop rotation. You should take at least a 3-year break in the cultivation of bulb vegetables in your area.We carry out a thorough selection of rash material, discarding rash bulbs and green onions with symptoms of diseases. After the onions are harvested, we remove all plant debris from the soil. In the case of growing onions after sowing, the seeds are treated with fungicides before sowing, e.g. Zaprawa Nasienna T 75 DS / WS in the amount of 0.3 g / 100 g of seeds.
MSc Eng. Agnieszka Lach
