What to Do When Onions Turn Yellow and Dry Up? Causes and Control Methods
Onion is one of the vegetables we commonly eat in daily life. Because of its high nutritional value and good planting returns, it is a main crop in many regions. However, as its planting area grows wider, the phenomenon of yellowing and drying up has become more and more serious, severely affecting onion production and reducing returns. So what are the causes of onion yellowing and drying up? Let's take a look.
1. Diseases
Disease is one of the main factors causing onion yellowing and drying up, and it can be divided into fungal diseases and bacterial diseases. Fungal diseases include gray mold, downy mildew and purple blotch, while the main bacterial disease is soft rot. When gray mold occurs, white lesions appear on the leaves, and gray mold layers appear under high humidity; when downy mildew occurs, yellow-white lesions appear on the leaves, white downy mold appears in damp conditions, and dry spots form in dry conditions; when purple blotch occurs, brown spots appear and gradually expand into purple lesions. Soft rot is manifested as yellowing of the leaves, and the bulb first shows water-soaked lesions, and finally the plant soft-rots and dies.
Control methods: Choose varieties with strong disease resistance, thoroughly disinfect and sterilize the seeds and the plot before planting, and spray pesticides in time when the disease occurs to prevent the condition from worsening and spreading. For fungal diseases, agents such as Previcur, Previcur and Iprodione can be used for control, with good results.
2. Pests
The pests that cause onion yellowing and drying up include red spiders, thrips and seed maggots. They gnaw on the leaves or root system, and in severe cases cause onion leaves to twist and turn yellow, and in the later stage they gradually dry up and die.
Control methods: Plow the land in advance before planting, turn the pests in the soil out and kill them with sunlight, then apply decomposed base fertilizer. Sugar-vinegar water can be used to trap and kill seed maggots and thrips larvae; for adults, beta-cypermethrin vinegar or beta-cypermethrin vinegar branches can be sprayed; for red spiders, Propargite and Mitex emulsifiable concentrate can be sprayed for control.
3. Physiological yellowing and drying up
When the soil is dry and lacks water for a long time during onion growth, yellowing and drying up will occur; if the soil is acidic, it will cause onions to grow slowly and become thin and weak, with leaves turning yellow and drying up. Yellowing and drying up also occur during high summer temperatures, and low-temperature freezing damage can also cause yellow leaves; a lack of certain trace elements or excessive fertility can also cause leaves to turn yellow and dry up. In addition, when controlling pests and diseases, improper use of pesticides causes phytotoxicity in the plants, resulting in yellowing and death over a large area.
Control methods: Water in time during drought, and also do a good job of drainage after rain to avoid root rot; for acidic soil, apply less or no fertilizers such as ammonium sulfate and superphosphate, and adjust the soil by spreading plant ash when applying base fertilizer. During high summer temperatures, water to lower the temperature, and also pay attention to low-temperature freezing damage; apply organic fertilizer to provide the plant with a variety of nutrients, and fertilization should also be reasonable and not excessive. When using pesticides, they must be used reasonably and the concentration must be noted; after phytotoxicity occurs, spray a relief agent for several decades.
The above is an introduction to the causes and control methods of onion yellowing and drying up. We hope it can help you. To learn more related knowledge, please stay tuned to us.