How is soybean downy mildew recognized? What are the methods of soybean downy mildew control?

Be sure to observe the growth of the plants, there will generally be gray-white moldy spots. Be sure to spray the agent in time, but also to avoid infecting other seedlings, and to dispose of the problematic parts in time.

It is the appearance of brown spots on beans and leaves, and the appearance of mold layer when the humidity is high. The prevention and control method is to select disease-resistant varieties, reasonable dense planting, and scientific management of water.

Judging mainly by the growth of soybeans, there are obvious signs of this disease. It is necessary to use chemicals in a timely manner, kill the germs in the soil in a timely manner, and properly ventilate.

Downy mildew is caused by the infection of the upper part of the soybean ground by Aspergillus flavus, which is a fungal disease, and the mold layer on the reverse side of the leaf is one of the clinical symptoms. Soybean seedlings, adult leaves, pods and soybean grains can all cause diseases. In the case of the onset of disease at the seedling stage, there is no disease in the young leaves, and the leaves gradually appear greenish spots from the bottom, and widen along the main and residual veins until all the leaves turn green.

Later, the same symptoms occurred throughout the leaves of the plant. Downy mildew is produced in spots in the field, spreading from a diseased core to the outside and <>

Moreover, the pathogen disease is obvious and easy to identify, so when the diseased plant is found in the field, the seedling can be removed immediately by the integrated shovel to reduce the source of initial infection. Soybean downy mildew, a fungal disease, caused by Aspergillus flavus infection, the disease is widespread, basically in the north and south of the soybean planting areas are produced, according to different conditions, the degree of harm is light and severe, affecting the final production, the situation can be serious to limit the production of about half.

Soybean downy mildew can cause adverse effects on the whole soybean plant, such as leaves, peas, soybean grains, etc., different positions are harmed, the symptoms presented are the same, but also different, soybean downy mildew hurts soybean grains, it is more appropriate to distinguish, there is a mildew layer on the surface of soybean grains, the hue is yellow-white or white, powdery, and there is a significant feeling when you touch it, in addition, the soybean grains that are more seriously damaged become black, dull and dull, do not receive, only give up.

In addition, when soybean downy mildew is more serious, there will be leaf bursting, soybean grains mold, etc., which will lead to a bad direct impact on production and quality. The best way to prevent downy mildew is to use the species with weak disease resistance, if it is not clear whether the selected species is disease resistance, it is recommended to select the seed dressing agent, and the dose is the net weight of the seeds. Because downy mildew spores can overwinter from diseased stems and residual leaves, and can also survive the winter in the soil, it is proposed to deal with dead branches and leaves in time after acquisition, and at the same time carry out more than three years of rotation to reduce the source of initial infection.

3. Prevention and control methods of all soybean downy mildew: (1) planting disease-resistant varieties.

Such as dandou. 8. Tiefeng 29, Tiefeng 30, etc.

2) Agricultural control.

Crop rotation. Crop rotation for more than 2 years in severely ill areas. Choose disease-free seeds.

Clean the countryside. After the soybean is harvested, deep ploughing is carried out to remove the residue of diseased plants in the field and reduce the source of bacteria. Strengthen field management.

Increase the application of phosphorus and potassium fertilizers, increase the number of tillage, promote the growth of plants, and improve disease resistance.

3) Pharmaceutical prevention and control.

Before sowing, the seed dressing can be carried out with pesticides, and the seed weight can be mixed with 35% Ruixin or 80% ethylene phosphorus aluminum dosage, or 50% carbendazim and 50% Fumei can be mixed in a ratio of 3:2 to the seed weight. In the early stage of the disease, it can be sprayed with 40% chlorothalonil suspension 600 times, or 25% methamalene wettable powder 800 times, or 58% methaloxine manganese-zinc wettable powder 600 times, or 69% anker manganese-zinc wettable powder 900 times.

1. All symptoms: mainly damage to leaves, pods and seeds, resulting in early defoliation, plant dwarfing, and reduced oil content and germination rate of beans. Large pale yellow patches appeared on the susceptible leaves at the seedling stage, and the lesions turned yellow-brown in the later stage.

When the weather is wet, white downy mildew may appear on the back of the lesion. Adult plants are susceptible, the initial leaf surface is scattered with many small yellow-green spots, and later becomes gray or gray-brown, there is gray-white downy mildew on the back of the leaf lesions, and when it is severe, the lesions are continuous, and the leaves are dry and fall early.

Prevention and control methods. Seed dressing with 50% fumerizin wettable by seed weight, or 70% dixone wettable, or 65% fumet, or 80% ethylphosphine aluminum, or carbendazim 50% wettable powder, or 35% methamethyl wettable powder.

At the beginning of the disease, spray 500-800 times of 50% Fumei double wettable powder, or 500-1000 times of 75% methalin wettable powder, or 1000 times of 77% copper hydroxide wettable powder, or 500-1000 times of 65% zeb wettable powder, or 800 times of 72% Kelu wettable powder, or 500-800 times of 75% chlorothalonil wettable powder, or 900-1000 times of 69% Anker manganese-zinc wettable powder. Spray once every 10 days, 3-4 times in a row.

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3. The pathogen and pathogenesis of all soybean downy mildew: (1) Pathogen: Soybean downy mildew is caused by the infection of the fungus of the subphylum Flagellates, the order Downy mildew.

2) Infection cycle.

Downy mildew overwinters on seeds, diseased pods and diseased residues with oospores. Becomes the first infestation of the second year**. After overwintering, oospores produce zoospores to infect the germ, enter the growth point, and then spread to the true leaf and axillary bud to form a systemic infection.

Later, a large number of sporangia grow on the diseased seedlings and leaves, which spread with wind and rain and then invade the host, spread among the host cells, and form sporangia and sporangia, so as to carry out multiple infections. After pod-setting, the fungus invades the pod with hyphae, causing the seeds to carry the fungus.

3) Onset conditions.

The rate of seed carrying and the source of bacteria in the field are related to whether the disease can occur. Where the seed carrying rate is high and the soybean continuous cropping field has many bacterial sources, the disease will occur severely. The occurrence and epidemic of downy mildew are related to the temperature, humidity and rainfall at the time of the onset.

7 The month of August has a lot of rainfall, which is conducive to the epidemic of diseases. 7 In August, there was little rainfall and drought was mild. There were significant differences in disease resistance among varieties, and planting susceptible varieties in a large area would create conditions for disease epidemics.