Identification and control techniques of soybean downy mildew

Downy mildew occurs more frequently in soybean producing areas in China, especially in northeast and north China during the soybean growth period, and the disease aggravates in rainy years, which seriously leads to premature fall or withering of leaves, mildew of seeds and a reduction of 30% to 50%. It is mainly harmful to leaves, pods and beans of seedlings or adult plants.

The pathogens on the diseased seeds caused the disease of the seedlings by systematic infection, but the cotyledons did not show symptoms. When the first pair of true leaves unfolds, chlorotic patches appear along both sides of the leaf veins and expand along the main veins and lateral veins. Causes the whole leaf to fade green, sometimes the whole leaf turns yellow. When the weather is rainy or wet, there is a gray-white mildew layer on the back of the disease spot, and the diseased leaves turn yellow, brown and dry. At the adult stage, the leaf surface was round or irregular, the edge was not clear yellow-green spots, then turned brown, and the back also produced a gray-white mildew layer. The disease spots often converge into large patches, and the diseased leaves dry up and die. The external symptoms of pod infection are not obvious, but the yellow mold layer, namely hyphae and oospores, often appears in the pod. The damaged beans are white and dull, and there is a layer of yellow-white powdery mold on the surface.

The pathogens overwintered by oospores on the diseased remains or seeds. The oospore attached to the seed is the main source of infection, and the infection chance of oospore on the diseased body is less. Oospores germinate with seed germination, produce zoospores, invade from the host Hypocotyl, enter the growing point and spread to the whole plant to become a systematic infection disease, and the diseased seedlings become the source of re-infection.

Prevention and cure method

1. The varieties with strong disease resistance were selected according to the local actual situation.

two。 According to the characteristics of pathogens, more than three years of rotation is advocated to reduce the source of primary infection.

3. The disease-free seeds were selected and treated with chemicals before sowing, and the seeds were mixed with 0.3% aluminum ethyl phosphate or 35% metalaxyl powder.

4. Strengthen field management. When hoeing, pay attention to eradicate the diseased seedlings infected by the system. Reduce the source of field infection. Reasonable close planting, increase the application of phosphorus and potassium fertilizer.

5. Spraying 600 times of 40% chlorothalonil suspension, 500 times of 50% carbendazim wettable powder or 800 times of 25% metalaxyl wettable powder can control soybean downy mildew.