A Detailed Guide to the Latest Control Measures for Soybean Downy Mildew

Soybean is an important food crop in our country, and downy mildew is a commonly occurring disease during cultivation. It is widely distributed around the world, and causes more severe damage especially in high-humidity areas. It can cause serious yield reductions and bring huge losses to farmers. So how should soybean downy mildew be controlled? Let's find out together.

1. Disease symptoms

Downy mildew mainly harms soybean seedlings, leaves and seeds, among which the seed incidence rate is relatively high. Sowing with infected seeds will cause seedlings to become diseased. After infection, the first true leaf will show chlorotic lesions at the base of the petiole. As the disease spreads to the entire leaf, the leaf turns yellow, and mold also appears on the back, which is the sporangia of the pathogen. Climate change can also have a certain impact on the development of the disease. Damp climate will intensify the development of the disease, and the mold layer will be relatively thicker. When the disease is severe, the seedlings cannot become established, and death occurs at the early stage; when the climate is dry, the disease development will be delayed, and there may not even be a mold layer.

2. Transmission pattern

The pathogen survives in diseased grains and tissues. After overwintering safely, it produces zoospores and attacks the seedlings. As the soybean grows, the mycelium increases and gradually causes damage to the true leaves and axillary buds. The probability of seedlings being attacked is affected by temperature. When the temperature is below 13 degrees, the incidence rate is about 40%, while when the temperature is above 18 degrees, the disease basically does not occur. After the disease occurs, the seedlings carry relatively large sporangia, which spread to other plants by wind and rain, causing leaves of other plants to become diseased. After the sporangia land on the leaves, they infect the epidermis, grow in the intercellular spaces, and the mycelium continuously increases. When the fungus invades the interior of the plant, chlorotic lesions appear, and after about 1 week sporangia are formed, continuing to expand the scope of damage. Light also has a relatively large impact on the germination of the pathogen's sporangia. The longer the light duration, the faster the germination; the shorter the light duration, the slower the germination. In wet and rainy years, downy mildew occurs more severely. It generally begins to occur in mid-to-late June, and the peak period is in July-August.

3. Control measures

Downy mildew is parasitic, so varieties with strong disease resistance should be cultivated. Screening seeds before sowing can reduce the incidence rate and remove some diseased seeds to prevent their seedlings from being infected. It is best to select seeds on disease-free days, and seed dressing with chemicals can also be used to avoid pathogen infection. When the disease appears, chemicals should be applied in time for propagation. Commonly used chemicals with good effects include 65% zineb wettable powder 500-fold solution and 50% tecloftalam wettable powder 800-fold solution, etc. The chemical should be sprayed evenly. At the same time, avoiding continuous cropping, carrying out reasonable crop rotation, increasing the application of phosphorus and potassium fertilizers, and draining accumulated water in time also help alleviate the occurrence of downy mildew.

The above is an introduction to the control measures for soybean downy mildew. We hope it can help you. If you want to learn more related knowledge, please stay tuned to us.