Onions are naturally very robust plants. Nevertheless, it can happen from time to time that diseases and fungi spread. Read here what they are and how to fight them.
Almost every hobby gardener has planted a few onions in his bed. They are indispensable in the kitchen, but onions can also provide some good services in everyday life. For example, if you've been stung by a wasp, an onion will help relieve the pain and keep the bite site from swelling.
You don't have to pay much attention to the cultivation of onions, as they are very undemanding plants. Diseases and pests rarely appear. As a rule, infections mainly occur when the weather is very humid for a long time, which is when fungi in particular have an easy time and multiply quickly. Today we 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 onions are also attacked more frequently. The trigger is the fungus Peronospora destructor, which can multiply easily in persistently wet weather.
» Identifying downy mildew
You can recognize downy mildew especially early in the morning when the dew is still moistening the leaves. Then you will see a purple-grey spore lawn, but you have to look very closely, preferably against the light.
A few days later, the color changes to a pale grey, and the foliage soon dies above the affected areas. The fungus multiplies above all on cool summer nights when the formation of dew is very strong. It is ideal for him when the sky is overcast during the day and the temperature does not rise above 20 degrees.
Infection usually comes from diseased bulbs that have overwintered in the ground. The spores can then be widely dispersed by the wind in the spring. You will then find the first infested onion plants around May. If the downy mildew infestation is very severe, the onions will not last as long and the yield will also be lower.
» Preventing/controlling downy mildew
Unfortunately, you cannot prevent infection in the home garden. At most, you can look for the most resistant varieties possible when buying. If you notice the infestation in 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 is primarily found on leeks after long periods of damp weather, but you can also often see it on the stalks of onions. In onions, purple spot disease is usually a consequence of downy mildew infestation.
» Recognizing purple spot disease
You can recognize the infection by the initially grey, oval spots. The elongated areas then take on a black color as the disease progresses, and they also have a purple border, hence the name of the fungal infection. In contrast to other pathogens, this fungus spreads relatively slowly. A stronger infestation can only occur if precipitation lasts longer.
» Prevent/control purple spot disease
The fungus usually only appears towards the end of the growth phase and does not cause any major damage to the onion plants. The fungus can survive in the soil on infected leaves. So you can prevent the disease by removing diseased parts of the plant.
➤ 3. Yellow Stripe
The so-called yellow stripe is caused by a virus. It also occurs on leeks, but the trigger here is a completely different virus that only affects the leeks. On the stalks and leaves of the onion plant you will see vertical stripes of bright yellow color that immediately catch the eye.
» Detect Yellow Lines
The virus not only affects onions, but can also spread to garlic, daffodils and shallots. Different species of aphids are responsible for transmitting the virus. As the disease progresses, the onion stalks atrophy and wither, and the onions usually remain smaller.
» Preventing/fighting yellow stripes
Controlling yellow stripe in the home garden is difficult, but since the damage is minimal, the infection can be tolerated.
These are the three main diseases you can deal with onions in your home garden. Flour disease, onion smut and paper spot disease should also be mentioned, but these are only very rarely found in the home garden.