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Soybean blight control method
Soybean blight, also known as bud blight, is a viral disease that significantly affects soybean yields. The extent of damage varies depending on the timing of infection, with losses ranging from 25% to 100%. This disease was first observed in imported soybean varieties in Shandong Province in 1962, and later spread to Hebei, Beijing, Liaoning, Jilin, and Heilongjiang. Although multiple viruses are suspected to cause the disease, no official pathogen has been identified, which means the causative agents may vary by region.
The symptoms of soybean blight are not always apparent during the seedling stage. Some plants may show rust-like spots on the leaves, but most remain asymptomatic at this point. Once flowering begins, the disease becomes more visible. Affected plants display a characteristic symptom: the top of the stem bends downward into a hook-like shape. The tender leaves, buds, and stems turn brown and easily fall off, while the pith inside also turns brown. The necrotic area spreads downward along the stem. On the petioles, brown streaks appear, and irregular brown spots develop on the pods. Interestingly, the leaves often show no visible signs of infection. Plants infected early in their growth cycle tend to be stunted, with fewer branches or even no branching at all. Other symptoms include dwarfing, excessive flowering buds, compound foliage, enlarged sections, and abnormally dark green leaves that persist until harvest. Despite these changes, the seeds of infected plants usually appear normal and do not show brown speckles.
The occurrence and severity of the disease vary greatly from year to year and region to region, and the full mechanisms of its spread are still not fully understood. Studies have shown that soybeans growing near perennial forage or wasteland are more likely to be infected early and heavily. In contrast, soybeans adjacent to non-host crops like corn tend to show later and milder infections. The disease can affect soybeans at any growth stage, but the plant is most vulnerable before flowering. Most soybean virus diseases are transmitted through infected seeds, and once the virus is present in the seed, it is difficult to eliminate. Treatments such as chemical seed soaking or using shoot culture methods are generally ineffective.
To manage the disease, several preventive measures are recommended. First, strengthening quarantine efforts is essential to prevent the spread of the disease. Second, breeding resistant soybean varieties and using virus-free seeds can help reduce the risk. Third, controlling aphids, which act as vectors for the virus, is crucial. At the seedling stage, insecticides such as 2.5% cypermethrin EC diluted 5000 times or 40% omethoate 2000 times can be applied. Alternatively, 3% carbofuran powder (2 kg per acre) mixed with 15 kg of fine soil can be used during sowing to control both aphids and cyst nematodes. Finally, intercropping soybeans with tall crops, planting early, and removing weeds from the field can all help lower the incidence of the disease.