What are the symptoms of downy mildew in soybeans? How to prevent it scientifically?

Symptoms: After the leaf is damaged, the leaf surface produces yellowing dots at the beginning, gradually turns gray-brown, when wet, the back of the leaf produces gray mold, and when it is serious, the leaf withers and falls off, and the whole plant dies. After the pod is damaged, a gray-white mold layer is formed on the surface of the seeds inside the pod, and the symptoms outside the pod are not obvious.

1. Select disease-resistant varieties and implement crop rotation for more than 2 years. 2. Reasonable dense planting, timely removal of diseased residues, deep soil turning, and reduction of pathogen sources. 3. Before sowing, soybean seeds should be mixed with 50 fumei double wettable powder with seed weight, or with 70 dixone, 80 acetphosphine aluminum or 35 rhizopus mildew with seed weight.

4. Spray pesticides for prevention and control in the early stage of the disease.

The onset is yellow-brown spots on the leaves. It mainly damages seedlings or adult leaves, pods and bean grains. Seedlings grown from diseased seeds can cause systemic disease, showing greenish patches from the base of the first pair of true leaves, expanding along the main and lateral veins, causing the whole leaf to turn green.

Fertilizer and water management and pest control can be strengthened.

It is mainly manifested on the leaves and branches, the leaves will turn yellow, and the branches and leaves will wither; It can be prevented with drugs, sprayed with 80% antibiotics, seeds should be treated before sowing, soaked in salt water before sowing.

When soybean downy mildew damages the leaves (from the seedlings can be harmed), there will be some small patches, in the case of seedlings, the color is relatively light (similar to greening), which will expand with the main vein and side veins, and in severe cases, the whole leaf will fade green.

If you are infected with downy mildew at the adult stage, at the beginning, there will be small spots that fade green, and then turn into small patches, from the outside, similar to the macula, and in the later stage, the color changes from yellowish brown, and the back of the leaf can be turned over, and a mold layer can be found to appear, and the color is gray.

1. Crop rotation planting.

Crop rotation is a good way to prevent downy mildew, especially a field planted with soybeans all year round, the occurrence of downy mildew will become more and more serious, and after 3 years of rotation planting with other crops, the downy mildew situation will be greatly improved.

2. Disease-resistant seeds.

Buying seeds with strong disease resistance can also effectively prevent the occurrence of downy mildew, and under the same conditions, seeds with strong disease resistance have its unique advantages.

3. Field management.

The field management mentioned here includes many aspects, such as reasonable dense planting, not too dense planting; Flood irrigation is prohibited to prevent excessive humidity in the field; Fertilizer should be plentiful but not excessive; Pay attention to the prevention of weeds in the field, etc., that is, our normal field management should be in place.

Answer]: The causative agent of soybean downy mildew is downy mildew in Northeast China, which belongs to the phylum Oomycetes. Downy mildew is common in soybean producing areas, and it occurs more often in cold areas.

It mainly harms seedlings or adult leaves, pods and beans. The seedlings grown from diseased seeds can be systematically diseased, and there are no symptoms in the cotyledons, and there are greenish patches from the base of the first pair of true leaves, which expand along the main vein and lateral veins, causing the whole leaf to turn green. Later, the leaves of the whole plant can be visible.

Before and after the flowering period, there is a lot of rain or high humidity, and the back of the lesion is imitating a gray mold layer, and the diseased leaves turn yellow and brown and dry up. The external symptoms of pod infection are not obvious, but the yellow mold layer often appears in the pod, that is, the mycelium and oospores of the fungus, and the affected bean grains are white and dull, and a layer of yellow-white powdery mold layer is attached to the surface.

The sporangia germinate to form a bud tube, which invades from the host stomata or between cells, and spreads between cells to absorb host nutrients by the sucker. The oospores attached to the seeds are the main source of primary infection, and the oospores can germinate with the germination of soybean, form sporangia and zoospores, invade the host hypocotyl, enter the growth point, and spread to the whole plant to become the diseased seedlings of systemic infection. The diseased seedlings have become the source of re-infection.

Prevention and control methods. Breeding of disease-resistant varieties: According to the dominant varieties of local pathogens, select and promote disease-resistant varieties, such as Zaofeng No. 5 and Baihua File in Jilin.

Seed treatment: Seed dressing with Chlormyces reviscosa, or Grammycolin, Formecis and Dixon. Removal of diseased seedlings:

The symptoms of diseased seedlings are obvious and easy to identify, and the diseased seedlings can be pulled out by combining cultivating and weeding to reduce the source of infection. Spraying agents: When the epidemic conditions of the disease appear, spray and control with enoylmorpholine, aluminum ethidronate, carbendazim, antibacterial special and so on as soon as possible.

Generally damage the leaves, the disease jump is generally on the upper leaves, the initial outline of the lesions is not obvious, light yellow, and then turn black, the back of the leaf is densely covered with a light purple mold layer, when the humidity is high, the more serious the disease. In case of continuous rainy weather, 45 chlorothalonil smoke removal agent 250 grams of smoke control can be used per mu, divided into 5 6 piles in the greenhouse in the evening, smoked overnight after being lit with a dark fire, ventilated the next morning, once every 8 10 days, there are many reasons for the disease of edamame, which may be the poor disease resistance of the variety, unreasonable fertilization, the soil is not suitable for planting edamame, environmental factors, weak plants, very dark light, etc.

There are four common pests and diseases in edamame, one is downy mildew, the second is gray mold, the third is gray spot, and the fourth is sclerotinia sclerotinia. Soybean mosaic disease is mainly caused by soybean mosaic virus, peanut streak virus, soybean dwarf virus, tobacco necrosis virus, alfalfa mosaic virus and other viral infections, sometimes alone, sometimes mixed infection.

Downy mildew, in which the fungus overwinters on diseased carcasses or seeds with oospores. In the second year, when conditions are ripe, oospores germinate to produce sporangia, which release zoospores, which are spread by rainwater sputtering, invade from the embryo, and infect the system. In the process of growing edamame, many chemical fertilizers and watering are under the control of farmers, such as powdery mildew, which generally occurs at the pod-setting stage, and there will be a white powdery object in the early stage, and then the powdery object will become a spot.

In the growth process of edamame, the implementation of many chemical fertilizers and the amount of watering are to be controlled by farmers, like powdery mildew generally occurs in the pod-setting stage, there will be white powdery objects in the initial stage, and then the powdery objects become spots, generally harming the leaves, the lesions generally appear on the upper leaves, the initial outline of the lesions is not obvious, light yellow, and then become black, and the back of the leaves is densely covered with a light purple mold layer, and the higher the humidity, the more serious the disease.

The leaves will turn yellow, and there will be various small yellow spots on the leaves, gray mold will appear, and there will also be symptoms of wilting.

After edamame and downy mildew, the entire leaf and leaf cake will turn white. And if the fruit has already been produced, the inside of the fruit will also rot. Severely affects yields.

The leaves will turn from green to yellow, and insects will gradually grow on the leaves, which will slowly cover the entire leaf until the entire plant is dead.

The first point is that there will be a lot of black dots on the edamame, which is very scary, so you should pay attention, the second point is that you will find that there will be a lot of bugs on the edamame, and there must be a virus at this time, and the third point is that the edamame does not grow very well, and there is also the phenomenon of yellow leaves, which should be paid attention to at this time.

Edamame downy mildew is characterized by small yellow spots on the leaves and sporangia on the dorsal backs of the leaves.

The disease is mainly manifested on edamame leaves, and there will be a lot of mold on the infected leaves.

Answer: Hello, soybean downy mildew is a disease caused by downy mildew in Northeast China and occurs on soybeans. It can be diseased during the growth period of soybean, and it is harmful to soybean seedlings, leaves, pods and grains. The most obvious symptom of the disease is downy mildew on the dorsal surface of the leaves.

Ask what to do if there is mycosis on the bean leaves and there are bean worms.

Ask if there will be any problems with the insects raised.

No questions will be asked. Is there any other way?

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.

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.

Prevention and control methods.

1. Agricultural measures: keep seeds from disease-free land and implement crop rotation for more than 2 years. Clean the farmland, collect the sick and residual bodies and burn them in a centralized manner, plough the land, carry out formula fertilization, and plant reasonably densely.

2. Pesticide control: use 35 methamethoxin seed dressing agent according to the weight of the seeds. Spray 1:1 at the beginning of the disease

1:200 times Bordeaux liquid, or 90 aluminum triacetylphosphate wettable powder 500 times liquid, or 70 Baidorfu wettable powder 500 600 times liquid, or 65 Baodasen 800 times liquid, or downy mildew carb water agent 600 times liquid, or 78% Kebo wettable powder 500 times liquid, or 56% downy mildew clear wettable powder 700 times liquid, or 69% Anker manganese zinc wettable powder 600 times liquid, or 50% methyl copper wettable powder 600 times liquid, or 90% 500 times of Physalin WP, or 400 times of 70% manganese wettable powder, 500 times of 72% Clomycin WP, or 600 800 times of 72% Kelu WP, or 60 0 times of 72% of Anti-Ling WP, or 1500 times of 50% Anker WP, or 58% of Methyl Frost & Manganese Zinc WP 500 times, 600 times of downy mildew water agent, 1500 times of inhibitory fast net (oxazole ketone and cyanide frosturea) water dispersible granules, or 64 500 times liquid of alum wettable powder and other agents, every 10 days or so l times, prevention and control 1 2 times.

For reference, thank you for your attention.

You're working well! Have fun!

To avoid resistance, alternate use.

It's all working well.

Carbendazim is a protective agent that can be sprayed to prevent disease before the disease develops.

This is not within the scope of today's answer, but you can ask a separate question.

Downy mildew control can be discussed.

The dosage varies from time to time.

At the beginning of the disease, spray 1:1:200 times Bordeaux liquid or 90% aluminum triethylphosphonate wettable powder 500 times, 60% chlorothalonil wettable powder 500 times, 72% gram dew or 72% frost urea manganese zinc (gram antiling) wettable powder 800 1000 times solution.

In areas that are resistant to the above-mentioned fungicides, 69% Anker manganese-zinc wettable powder or water-dispersible granules can be used 1000 times of liquid, once every 10 days or so, and 1 or 2 times for prevention and control.

Strengthen field management at the peak of the disease, clean the field, eradicate weeds, reduce pathogens, and uproot serious diseased plants as soon as possible; Chemical control: 25% methalene wettable powder can be used for seed dressing, and 72% frost urea and manganese zinc wettable powder 800 1000 times liquid? Downy mildew carb hydrochloride aqueous agent 700 1000 times liquid?

1000 times of 69% mancozeb and enoylmorpholine wettable powder, choose one of them for control.

You're welcome, if you don't understand something, please consult**.