Onion purple spot disease, also known as black spot, maculopathy, mainly damage leaves, pedicels. The lesions are prismatic, white and yellow, and the lesions are enlarged and purple. When the air is wet, the surface of the lesion is black moldy, with concentric ring veins, yellow halos around, and yellow or broken leaves and pedicels.
Prevention:
1. Two-year rotation with non-onion vegetables, with more potassium fertilizer;
2. Sterilize with formalin 300 times for 3 hours.
3. Put bulbs in warm water of 40°C-45°C for 90 minutes;
4, with the following agents control:
175% chlorothalonil 500 to 600 times spray control;
264% anti-virus 500 times spray control;
358% metalaxyl manganese zinc 50 times spray control.
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