Causes of yellowing and drying of onion and its control methods

Onion is one of the most common vegetables in our life. Because of its high nutritional value and good planting efficiency, onion is the main crop in many areas. However, with the wider its planting area, the phenomenon of yellowing and drying is becoming more and more serious, seriously affecting onion production and reducing income, so what is the reason for onion yellowing and drying? Let's take a look.

1. Disease

Disease is one of the main factors causing onion yellowing and drying, which can be divided into fungal diseases and bacterial diseases, fungal diseases include Botrytis cinerea, downy mildew and purple spot, and bacterial diseases are mainly soft rot. When Botrytis cinerea occurs, a white spot will be selected on the leaves, and a gray mildew layer will appear in the humidity; when downy mildew occurs, the leaves will appear yellow-white spots, wet white velvet mildew, and dry spots; when purple spot disease occurs, brown spots will appear and gradually expand into purple spots. The soft rot was characterized by yellowing of leaves, waterlogged spot at the beginning of the bulb and death of the plant at last.

Control methods: select the varieties with strong disease resistance, thoroughly disinfect the seeds and plots before planting, and spray chemicals in time to prevent the disease from worsening and spreading. Fungal diseases can be controlled with Prike, Prodnisolone and other agents, and the effect is better.

2. Insect pests

The pests that cause onion yellowing and withering are red spiders, thrips and seed flies, which nibble on leaves or roots, seriously cause onion leaves to twist and yellowing, and gradually wither to death in the later stage.

Control methods: plough the land ahead of time before planting, dig up the pests in the soil, use sunlight to kill them, and apply rotten base fertilizer. The larvae of seed flies and thrips can be killed by sweet and sour water, the adults can be sprayed with high-efficiency cypermethrin vinegar or high-efficiency cypermethrin vinegar, and red spiders can be sprayed with propargite and mikexin EC.

3. Physiological yellowing and drying up

When the onion grows, the soil will be yellowed and dry when the soil is dry for a long time; if the soil is acidic, it will cause the onion to grow slowly, thin and weak, and the leaves will turn yellow and dry. Yellowing and drying will also occur in summer high temperature, low temperature freezing injury will also be yellow leaves; lack of certain trace elements or excess fertility will also lead to yellowing and drying of leaves. In addition, in the prevention and control of diseases and insect pests, improper use of pesticides, resulting in plant damage, will appear the phenomenon of yellowing and death of the area.

Prevention and control methods: timely watering during drought, drainage measures should also be done after rain to avoid rotting roots; for acid soil, ammonium sulfate, calcium superphosphate and other fertilizers should be less or not applied, and the application of base fertilizer can be adjusted by spreading plant ash. In summer high temperature should be watered to cool down, at the same time pay attention to low temperature freezing injury; topdressing organic fertilizer to provide a variety of nutrients for plants, while fertilization should be reasonable, should not be too much. In the use of chemicals must be reasonable, pay attention to the concentration, after the occurrence of drug damage to spray relief drugs for decades.

The above are the reasons for the yellowing and drying of onions and the introduction of prevention and control methods. I hope I can help you. If you want to know more about it, please follow us.