Symptoms: Onion black spot disease has risen as the major onion disease in recent years, mainly damage the leaves and pedicels, and the strains are more susceptible to disease. Yellow and white chlorotic long round spots initially appear on the leaves. After the rapid expansion of up and down, the formation of shuttle-shaped lesions, become dark brown, yellow halo with the edge. The condition continues to expand, with spots and patches remaining in a fusiform shape, and the appearance of a ring-streak appears on the lesions. In the late stage of disease, dense black fungus layer, conidial stems and conidia, was found on the lesions. The upper part of the diseased leaves was chlorosis and dry or the stems were broken.
Control methods
(1) Agricultural control. Apply organic base fertilizer, increase application of phosphorus and potassium fertilizer, close planting, remove field sickness, and seriously implement 2~3 year rotation of non-onion crops. Strengthen field management, timely drainage after heavy rain, promote robust growth of plants, and increase plant disease resistance. (2) Chemical control. 70% chlorothalonil WP 600 times or 50% acetaminophen wettable powder 1000 times; 70% WP WP 600 times or 14% urea copper 300 times, can also be used 1 : 0.5:200 Bordeaux mixture, sprayed every 5 to 7 days, and sprayed 3 to 4 times.