Prevention and control of soybean top blight

Soybean top blight, also known as bud blight, is one of the soybean virus diseases that have a great impact on yield. Due to different periods of onset, the loss caused was 25% to 100%. Similar symptoms occurred in foreign varieties introduced in Shandong Province in 1962, and then occurred in Hebei, Beijing, Liaoning, Jilin, Heilongjiang and other places. The disease is caused by a variety of viruses, but the pathogen has not been formally identified, so the pathogen of top blight may be different from place to place. 1. Disease symptoms: most soybean varieties showed no obvious symptoms at seedling stage, only a few rusty spots appeared on the leaves. Typical symptoms appear after flowering, the top of the diseased plant stem bends downward into a hook, the tip of the tender leaves, buds and stems turn brown, dry and easy to fall off, and the pith also turns brown. The necrotic part spread downward. There are brown necrotic stripes on the petiole and irregular brown necrotic spots on the pods, and the leaves often show no symptoms. The plants with early onset were obviously dwarfed, without pods or few pods, and some were unbranched. In addition, the diseased plants can also appear dwarfing, flower buds and compound leaves, node expansion, abnormal dark green leaves, green and dark green in the harvest season, and the seeds of the diseased plants look normal and do not produce brown spots. 2. Incidence regularity: the occurrence and prevalence of top blight vary greatly between years and regions, but the epidemic rule has not been fully understood. The investigation shows that the disease of soybean near perennial forage and wasteland is early and severe, while that of soybean fields adjacent to non-host crops such as corn is late and light. Soybeans can be susceptible to disease at any growth stage, and the disease rate is high before flowering. Most soybean virus diseases can be transmitted by seeds with virus, but it is difficult to detoxify seeds with virus, and it is ineffective to treat seeds with chemicals or grow point culture. 3. Prevention and control methods: ① strengthens quarantine to prevent the spread of diseases. ② selected disease-resistant varieties and adopted avirulent seeds. ③ control of aphids can reduce the damage of virus diseases, spraying 2.5% EC at seedling stage, or using 3% furan powder 2 kg mixed with 15 kg of moist fine soil per mu for sowing, and controlling grubs and cyst nematodes. Intercropping of ④ soybean with long-stalk crops, early sowing at the right time and removal of weeds in the field can reduce the disease.