Onions are naturally very robust plants. Nevertheless, diseases and fungi can spread from time to time. Read here what these are and how they can be combated.© Goffkein - Fotolia.com Almost every hobby gardener has planted a few onions in his bed. They can hardly be imagined in the kitchen, but the onion can also do some good work in everyday life. For example, if it was stung by a wasp, an onion will help relieve the pain and prevent the puncture site from swelling.
You don't have to pay much attention to growing the bulbs as they are very undemanding plants. Diseases and pests rarely appear. As a rule, infections occur above all when the weather is very damp for a long time, then mushrooms in particular have an easy time and multiply quickly. Today, we will explain the most important onion diseases and how you can recognize and combat them.
The 3 most common onion diseases
➤ 1. Downy mildew
Downy mildew is widespread in domestic gardens, and the onion is also affected more often. The trigger is the fungus Peronospora destructor, which can multiply easily in persistently damp weather.
»Detect downy mildew
You can recognize downy mildew especially in the early morning, when the dew still provides moisture on the leaves. Then you see a spur grass in violet-gray color, but you have to look very carefully, preferably against the light.
A few days later, the color changes to pale gray, and the leaves soon die above the affected areas. The fungus multiplies especially on cool summer nights when the dew formation is very strong. It is ideal for him when the sky is covered during the day and the temperature does not rise above 20 degrees.
The infection usually comes from sick onions that have overwintered in the ground. The spores can then be widely distributed by the wind in spring. You will then find the first infested onion plants around May. If the downy mildew is very strong, the onions will not last as long and the yield will also be lower.
»Prevent / combat downy mildew
Unfortunately, you cannot prevent infection in the home garden. You can only look for varieties that are as resistant as possible when buying. If you notice the infestation in good time, you can try to control it with a fungicide.
➤ 2. Purple spot disease
Purple spot disease is also caused by a fungus, namely Alternaria porri. It can primarily be found on leeks after prolonged, damp weather, but you can also often see it on the onion tubes. In the case of onions, the purple blotch disease is usually a secondary disease after downy mildew.
»Detect purple spot disease
You can recognize the infection by initially gray, oval spots. The elongated spots then turn black in the further course of the disease, and they also have a purple border, hence the name of the fungal infection. In contrast to other pathogens, this fungus spreads relatively slowly. Only if precipitation lasts longer can a greater infestation take place at all.
»Prevent / combat purple spot disease
The fungus usually only shows up towards the end of the growth phase and does no greater damage to the onion plants. The fungus in the soil can survive on infested leaves. You can prevent the disease by removing diseased parts of the plant.
➤ 3. Yellow streaking
A so-called yellow streak is caused by a virus. It also occurs on leeks, but here the trigger is a completely different virus that only affects the leek. On the vents and leaves of the onion plant you can see longitudinal stripes in bright yellow color that immediately catch the eye.
»Detect yellow streaking
The virus not only affects onions, but can also spread to garlic, daffodils and shallots. Different types of aphids are responsible for the transmission of the virus. In the course of the disease, the onions are atrophied and withered, the onions usually remain smaller.
»Prevent / combat yellow streakiness
Combating yellow streaking is difficult in the home garden, but since the damage is minor, you can tolerate the infection easily.
These are the three most important diseases that you can deal with onions in the home garden. Also worth mentioning are the flour sickness, the onion fire and the paper stain disease, which are, however, only very rarely found in the garden.