Why do Onions turn yellow and dry?

1. Fungal diseases

(1) mainly include gray mold, downy mildew and purple spot.

(2) Prevention and control points: select disease-resistant varieties and select disease-free plants; Seed treatment before sowing, soak the seeds in warm water for 30 minutes; Avoid crop rotation for more than 2 years; Strengthen fertilizer and water management, pay attention to the removal of disease residues; At the beginning of the disease, spray once every 7 to 10 days, 77.2% of downy mildew can be selected 800 times the liquid, 64% of virulent alum wettable powder 500 times the liquid, 80% of Zhuanshengwettable powder 500 times the liquid; Gray mold can be selected 50% sukline wettable powder 1500 ~ 2000 times liquid, 50% prohyline wettable powder 1500 ~ 2000 times liquid; Purple spot disease can be selected 64% virulent alum wettable powder 500 times liquid or 50% prohydne wettable powder 1500 times liquid.

2, bacterial diseases (1) mainly onion soft rot. (2) Prevention and control points: avoid continuous cropping, pay attention to the eradication of underground pests; Avoid spreading to the heart leaf when topdressing; Avoid flooding when watering; 72% agricultural streptomycin soluble powder 3000 times the solution or 58% risone 600 times the solution.

1. When the onion is seriously harmed by the larvae of seed flies (ground maggots), red spiders, and thrips, it is manifested as yellowing, leaf distortion, and dry in the later period.

2. The main points of prevention and control should be applied to mature fertilizer to lure and kill adult flies; Adults can choose 2.5% efficient cypermethrin vinegar 2000 times liquid, or 20% Kiuma emulsion 3000 times liquid, larvae can use 50% phoxiphos 800 ~ 1000 times liquid irrigation. Anti-red spider can be used 73% grams of mite 2000 ~ 3000 times liquid or 20% acaracide cream 1500 ~ 2500 times liquid control. 1. Key points of drought prevention and control: increasing the application of organic fertilizer; According to the different growth period of onion water demand, timely and appropriate watering; Ensure adequate water during vegetative growth. 2, soil acid damage prevention points: increase the application of organic fertilizer; Reduce the use of acidic fertilizers.

3. Prevention and control of yellowing and drying caused by high temperature and freezing damage; In case of high temperature should water cooling; Pay attention to prevent cold damage.

4, the prevention and control of yellowing and drying caused by drug damage: scientific grasp of drug concentration, reasonable proportion; Spray evenly when spraying; Chemical damage can be sprayed 0.05% green wind 95, using 500 times liquid or potassium dihydrogen phosphate 500 times liquid.