Recently, there are many rainy days, and the air humidity and soil moisture are large. This causes serious purple onion onset, which greatly affects the yield and quality of Welsh onion. Paying attention to the early identification of diseases and early prevention and control are crucial for ensuring the safe growth of Welsh onion.
First, the harm symptoms
The main damage leaves and pedicels, the initial generation of water-soaked white dots, expanded lesions were oval or spindle-shaped, from light brown to purple brown, with a yellow halo around the periphery. When the onset is severe, the lesions can go around the leaves and pedicels for one week, causing the onion leaves and flowers to die or break, the seeds shrinking, and the quality is poor.
Second, the incidence of the law
The incidence of heavy rains and heavy dew weather is heavy in the autumn; the plots of bad plots and poorly-drained crops are heavier than the earlier ones; the sowing is too early, the planting is too dense, the management is extensive, the ventilation and light transmission are poor, and the lack of fertilizer is harmful to the onion thrips The heavy field is heavier.
Third, transmission routes and conditions
Onion purple spot is a fungal disease caused by Onytis sp., which causes the mycelia to overwinter in the host or with the diseased body in the soil. In the following year, conidia are produced by airflow or rainwater, and are passed through the stomata, wounds or directly worn. Penetration through the epidermis, incubation period of 1 to 4 days. The sporulation of pathogenic bacteria requires high humidity, germination and invasion require the presence of water droplets, and thus the disease is heavy and humid.
Fourth, control methods
1. Clean the pastoral. After the harvest, the diseased body was promptly removed and taken out of the field to be buried or burned, and the soil was deeply turned to accelerate decomposition of the diseased body.
2. Strengthen field management. Wet the cultivator and open the drainage ditch to prevent water damage caused by rain.
3. Chemical control. At the beginning of the disease, 75% chlorothalonil 500-600 times solution, 64% antivirus 500 times solution, 72% metalaxyl manganese zinc 500 times solution, 3% polyoxin 800 times solution, etc. are sprayed 7 days before spraying. , Even spray 2 or 3 times, can effectively control the spread of the disease.
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