Diseases of onions are not so rare. What should be done in order not to lose the crop grown and pledged for storage? The answer to this question can be found in our article.
Having spent a lot of time and effort on growing an onion, it's a shame to lose it a month or two after putting it in storage. To avoid such a development of events, it is important to "know in person" the diseases that this vegetable is most often exposed to during storage, as well as methods of dealing with them.
Neck rot (gray rot of the neck of the bulb, gray neck cervical rot) is a fungal disease that can affect both turnip and onion sevok. The disease is caused by the onion (Botrytis allii) fungus that penetrates into poorly ripe or underdried bulbs. The source of infection is most often infected planting material and plant residues that have not been removed from the garden.
In the field, infection develops best with high humidity and low air temperature, and in storage - if it is too warm.
If the summer is rainy, you may notice the first signs of neck rot in late July - early August, when the onion is still growing in the beds, and its leaves are just starting to fall down. However, most often the disease is found a month or two after laying bulbs for winter storage.
What do infected heads look like? At first, they are no different from healthy bulbs. However, gradually the scales of their necks turn brown and become watery, as if boiled. Over time, the rot spreads throughout the bulb, and the scales become covered with gray mold. Then on the surface of the head appear small black sclerotia, which form a solid crust.
Sick onions begin to produce an unpleasant odor and gradually dry. If you miss the moment and do not remove them from the storage in time, the entire crop will be infected.
Onion varieties with dark-colored scales are affected by neck rot much less frequently than light-colored onions. And early ripening varieties and hybrids are less susceptible to ailment than later ones.
Is it possible to protect your crop from neck rot? Of course yes! To do this, you only need to follow the basic rules of planting and storage of onions:
- plant onion sets as early as possible and in a well-lit and ventilated area of the vegetable garden;
- immediately before planting, dress the seed with 3% suspension of TMTD (30 g per 1 l of water) or Ridomil Gold MC 68 WG century. (10 g per 4 liters of water);
- provide the necessary dressing for plants (apply nitrogen fertilizers only in the first 8 weeks after planting in the ground; in the second half of the growing season, feed the onions only (!) with potash-phosphate fertilizers);
- in a timely manner, before the arrival of prolonged rains, remove the onions from the field, and before putting them into storage in a dry, well-ventilated room, dry the vegetables thoroughly;
- It is mandatory to burn all the parts of the plants that will remain after harvesting and reassembling the onions;
- during the growing season, as well as during the winter storage of onions, remove diseased plants in a timely manner.
Donets rot (fusarium, fusarium rot) is a less common disease than neck rot. Its causative agent is a fungus of the genus Fusarium, which can be stored in the soil on plant residues for 5 years. In some cases, the source of the infection is infected seedlings, which, inadvertently, were planted in the spring.
The disease manifests itself in the summer when the weather is hot or already during the storage of onions.
The optimum temperature of the soil for the development of the fungus, the causative agent of Fusarium, is 27-32 ° C.
Among the first symptoms of fusarium that should alert you are the darkened leaves and the pink bloom formed at their base - spores of the fungus.
Over time, the diseased bulbs will stop growing, will become soft, their roots will darken and begin to rot, and white mycelium will form near the Donets.
In order to finally be convinced of the “diagnosis”, you can cut the diseased vegetable into two halves: with Fusarium, the lower part of the bulb scales will be watery, pale gray in color.
Some of the bulbs damaged by the fungus will die in the beds, the rest - in the store.
Especially fast onion tip rot develops in poorly ventilated rooms.
For the prevention and control of fusarium, you should take the same measures as for the control of neck rot. In particular, before planting a healthy sevok carefully sort, and then within 20 minutes process with 3% suspension of TMTD. Do not forget also to properly harvest and store crops and on time to remove diseased bulbs.
The causative agent of the disease is the bacteria Pectobacterium carotovorum and Bukholderia cepacia.
How does onion bacteriosis develop? First, a portion of the flakes of an infected bulb changes color from golden to greyish brown. Gradually, they become covered with mucus, become soft and begin to emit an unpleasant odor. And soon the rot spreads over the entire surface of the bulb.
Bacteriosis causes weakened, as well as early harvested and poorly dried onions
To protect plants from bacteriosis, observe agricultural practices and prevent fungal diseases. For example, 20 days before harvesting, spray the crop with a 1% solution of Bordeaux mixture. After all the bulbs have been removed from the ground, immerse them for 15 minutes in a 1% solution of mercuric chloride, and then dry thoroughly. Buried bulbs do not forget to sort out every 3-4 weeks.
Blue mold (penicillus, blue-green mold, green mold rot) develops when onions are stored in musty, damp, poorly ventilated rooms. Its causative agent are the fungi of the genus Penicillium.
Plant leaves are rarely affected. If, however, this occurs, light yellow watery spots appear on them, covered with blue-green mold.
With the progression of the disease, usually 2 months after putting the crop into storage, watery brown spots and bluish spores appear on the bottom and side scales of infected bulbs. At the same time, the internal succulent flakes swell up, turn brown-gray and begin to rot, becoming a source of unpleasant odor.
Infected plants that are stored in a dry place gradually dry out.
Mechanical damage, high humidity and low temperatures in storage contribute to the development of blue mold.
If you want to protect your crop from blue mold, immediately after harvesting, discard diseased and mechanically damaged plants, and store healthy, well-dried bulbs in a well-ventilated room, the humidity of which does not exceed 70%.
Between the diseases described onions are much more common than it seems at first glance. Prevention and control measures are also very similar. To save your crop from such misfortunes as neck rot, bottom rot, bacteriosis, blue mold, be attentive and scrupulous when choosing a place for planting onions, carefully care for the crop during the growing season, follow the basic rules for its collection and storage. And most importantly - do not forget about crop rotation: plant onions in the same place after at least 4 years.
Have a good harvest!