Lettuce downy mildew has a high incidence, what is the cause of lettuce downy mildew?

Lettuce downy mildew uses 600 times 58% mefluoromanganese zinc wettable powder, 500 times 69% alkenyl manganese zinc wettable powder, 700 times 80% mancozeb wettable powder, 600 times 72% mefluoromanganese zinc wettable powder or 600 times 50% ethylphosphine aluminum-manganese-zinc wettable powder. Downy mildew is an important disease of lettuce that often causes leaf death. Symptomatic leaves often flare up from the bottom up.

At first it is pale yellow, nearly round, and gradually expands into polygons. There is white mold on the back of the lesion when wet, and white mold on the front of the leaf spot when it is severe. The lesions enlarged, many of them joined together, and they died yellow-brown, causing the whole leaf to wither and die.

The apical branches of the sporangia are tea-shaped, with 3 or 5 short peduncles on the margins, each with a sporangium. The sporangia are oval or oval in shape. The sporozoites produced by the sporangia are scattered and become infected.

The pathogen overwinters with mycelium in seeds, oospores in soil, and lettuce from diseased residues or protected areas. In the second year, when conditions are right, sporangia are produced, which are spread by air currents, rain, and insects. The optimal temperature for spore germination was 6 10 and the optimal temperature for infection was 15 17.

Therefore, low temperature and high humidity are the main conditions for the onset of the disease. If it rains in the spring and cold and rainy in the fall, the disease is serious. Planting too densely, too much watering, too much, late unwrapping, no wind, etc.

Choose disease-resistant varieties. For example, purple lettuce, green hemp leaves, pointed leaves, and so on. Revolve.

Crop rotation with leguminous or Solanaceae vegetables. Strengthen cultivation and management. Diseased and residual leaves can be prevented by removing them, planting them densely, watering them with small water, and blocking the wind frequently.

Downy mildew is a common and serious disease in cash crops, which is very severe, has a fast onset and spreads quickly, and if not prevented in time, it will cause devastating losses to crops. In addition, downy mildew is widely infected in crops and can occur from seedling to harvest. It is difficult to prevent and control, with a high rate and great harm.

After the central disease plant is found in the field, it is necessary to spray 600 times of 75% chlorothalonil wettable powder, 400 times of 64% disinfectant alum wettable powder, and 600-800 times of 25% methamphetamine wettable powder as soon as possible. 40% aluminum phosphate wettable powder 200 times. Control methods include the selection of disease-resistant varieties, cultivation in fertile sandy loam soils, and the application of plantar fertilizer, especially potassium, to the soles of the feet.

It is strictly forbidden to flood irrigation during the melon sitting period, prune and prune in time, and maintain good ventilation.

Generally, it should be prevented 5 days before the onset of the disease, and the commonly used chemicals are 40% aluminum phosphate wettable powder 250 times or 50% frosted copper phosphate wettable powder 500 times, DuPont Kelu wettable powder 600-800 times. The above fungicides are used alternately, downy mildew is generally caused by fungi, and fungicides are used. Good fungicides include malingering, mancozeb, etc.

At present, the special drug enoyl cream urea cyanide on the market is a compound of enoylmorpholine and cyanuric acid, which has a special effect on double toxicity. In the countryside, there is also a saying that spring lettuce is a thousand yuan for spring lettuce. Although its taste is slightly bitter and slightly cold, it is beneficial to the viscera, soothing the pulse and facilitating the effect.

Therefore, it is also defined as a health food with high nutritional value.

The occurrence of diseases is closely related to climatic conditions, especially temperature and humidity, and low temperature and high humidity are conducive to the development of diseases. In early spring, when the low temperature rises to more than 6, when it is foggy and rainy, the sun exposure and too high temperature are not conducive to the occurrence of downy mildew of lettuce, which is at a low tide. But in autumn, when it rains prolonged, the disease becomes more severe.

At the same time, the planting is too dense, the ventilation and light transmission are poor, the watering is too early after planting, and the soil is moist or poorly drained.

It is because of the lack of nutrients in the base fertilizer during planting, and the lack of water, and it has been under the unventilated environment, so it will appear this germ.

It is likely that the planting temperature is not particularly high, or it may be because the planting density is relatively large, or the nitrogen fertilizer is applied more, or it may be because the light transmission conditions are not particularly good.

It's the weather temperature, and the soil, no nutrients, no moisture, no fertilization, and no pesticides.

Downy mildew is a relatively common occurrence in cash crops, the harm is very serious, the disease is violent, the onset is fast, the spread is fast, the spread is fast, if not timely prevention and control, it will cause devastating losses to crops, and downy mildew infects crops is also relatively wide, from seedlings to harvest can occur at all stages, the difficulty of prevention and control is relatively large, the first is very high, and the harm is relatively large.

After the central diseased plants are found in the field, it is necessary to spray 600 times of 75% chlorothalonil wettable powder, 400 times of 64% alum wettable powder, and 600 to 800 times of 25% methamethoxine wettable powder as soon as possible. 40% ethyl phosphorus aluminum wettable powder 200 times liquid for control. Control methods Choose disease-resistant varieties, choose fertile sandy loam soil for cultivation, apply foot fertilizer, especially potassium fertilizer, and strictly prohibit flood irrigation during the melon setting period, timely pruning, pruning, and good ventilation.

Spray foliar fertilizer on poor growth seedlings. Downy mildew spreads through the airflow, the onset of the disease is rapid, the spray must be timely, generally in the first 5 days to prevent, the commonly used agents are: 40% ethylphosphine aluminum wettable powder 250 times liquid, or 50% methyl frost phosphor copper wettable powder 500 times liquid, DuPont Kelu wettable powder 600 800 times liquid, the above fungicides should be used alternately, 5 7 days 1 time, spray 3 4 times.

Downy mildew is generally caused by fungi with fungicides. Good fungicides include Vicant, mancozeb, etc., and the specific drugs on the market. Frost urea is cyanide, which is a compound of enoylmorpholine and urea cyanide, which has a special effect on double toxicity.

In the countryside, there is also a saying that "spring lettuce race is a thousand gold"; Lettuce in spring is a golden vegetable, although its taste is slightly bitter and cold, it has the effect of benefiting the organs and soothing the pulse and facilitating the qi, so it is also defined as a health food with high nutritional value by the folk.

In the early stage, there will be light yellow, nearly round or polygonal lesions on the leaves, when the air is humid, the white mold layer will occur on the back of the leaves, sometimes it can spread to the front of the leaves, and the lesions will gradually turn yellow-brown with the aggravation of the disease, and when the disease is severe, multiple lesions will be connected together, and the whole leaf will wither and die, and the leaves will rot in a humid environment.

The lower leaves of the plant will produce yellowish lesions, with a white mold layer on the back, and the later lesions will turn yellowish-brown, which will cause the leaves to turn yellow and dry up.

The general symptom is that it will also appear yellow, and it will attract a lot of small insects around the roots, which will cause them to ulcerate and wither, which will make their growth rate very slow.

It is that you will find that the surface of the leaf will be wrinkled, and there will be yellowish strips, which will look like it is dry, and there will be symptoms of rot.

Abstract 1Downy mildew can be identified from the following hazard characteristics: polygonal yellow leaf spots on the leaves at the beginning of the stage.

The hazard characteristics of gray mold are also different: at first, gray-brown mold spots, initially hairy, later develop into clumps of clumps.

The approximate conditions for the onset of these two diseases are as follows:

1.The appropriate temperature for pathogen infection is 15 17, and it is easy to get sick when the greenhouse or open field reaches this environment;

2.Heavy fog and dew, severe disease under high humidity;

3.The soil is heavy in clay soil, low furrow plots, and the disease is severe in plots with partial nitrogen fertilizer.

Note: In fact, the prevention and control of diseases is best to start with the disease conditions, improve the environment for the growth of good vegetables, and prevent the contact and infection of germs.

Let's talk about the identification of common diseases of lettuce and their prevention and control measures.

3. Prevention and control reminders.

1.Regardless of the greenhouse or the open field, observe the changes in the weather in real time, and ventilate and reduce humidity in time;

2.Water reasonably, drain water in time, and don't let the ground get too wet;

3.Reduce the use of nitrogen fertilizers and increase the application of organic fertilizers and phosphorus and potassium fertilizers;

4.If diseased plants are found, remove diseased leaves and plants in time, and add pesticides to prevent and control germs quickly.

Note: The prevention and control of any disease pays attention to a "prevention first, comprehensive prevention and control", I don't know if you have done it, and at the same time, "prescribing the right medicine" is also a key point. After the onset of crops, we try to identify what kind of disease is, downy mildew is a disease caused by a fungus, and gray mold is caused by a higher fungus, and each has a very different medication.

I can't really tell the difference, and I can mix the drugs.

What is the difference between lettuce downy mildew and gray mold?

1.Downy mildew can be identified from the following hazard characteristics: polygonal yellow leaf spots on the leaves at the beginning of the stage.

The hazard characteristics of gray mold are also different: at first, gray-brown mold spots, initially hairy, later develop into clumps of clumps.

The approximate conditions for the onset of these two diseases are as follows:

1.The appropriate temperature for pathogen infection is 15 17, and it is easy to get sick when the greenhouse or open field reaches this environment;

2.Heavy fog and dew, severe disease under high humidity;

3.The soil is heavy in clay soil, low furrow plots, and the disease is severe in plots with partial nitrogen fertilizer.

Note: In fact, the prevention and control of diseases is best to start with the disease conditions, improve the environment for the growth of good vegetables, and prevent the contact and infection of germs.

Let's talk about the identification of common diseases of lettuce and their prevention and control measures.

3. Prevention and control reminders.

1.Regardless of the greenhouse or the open field, observe the changes in the weather in real time, and ventilate and reduce humidity in time;

2.Water reasonably, drain water in time, and don't let the ground get too wet;

3.Reduce the use of nitrogen fertilizers and increase the application of organic fertilizers and phosphorus and potassium fertilizers;

4.If diseased plants are found, remove diseased leaves and plants in time, and add pesticides to prevent and control germs quickly.

Note: The prevention and control of any disease pays attention to a "prevention first, comprehensive prevention and control", I don't know if you have done it, and at the same time, "prescribing the right medicine" is also a key point. After the onset of crops, we try to identify what kind of disease is, downy mildew is a disease caused by a fungus, and gray mold is caused by a higher fungus, and each has a very different medication.

I can't really tell the difference, and I can mix the drugs.

We can not only see the vigorous growth of spring lettuce in the vegetable garden, but also see it being planted on a large scale as a pillar industry for farmers to create wealth and increase income in the economic field; Some growers have reported that in the process of large-scale planting of lettuce, they often encounter downy mildew as the damage of lettuce growth and adult period, and light yellow, nearly round or polygonal lesions will appear on the leaves in the early stage, and when the air is humid, the white mold layer will occur on the back of the leaves, which can sometimes spread to the front of the leaves, and gradually become yellow-brown with the aggravation of the disease, and when the disease is severe, multiple lesions are connected together.

It is heavily damaged at the adult stage. The seedling stage can cause dead seedlings and stiff seedlings, and the functional leaves will rot and loosen the balls during the growth stage, which will affect the yield and commerciality. The main damage to the leaves, starting from the basal leaves, initially produces pale yellow near-round or polygonal corner spots on the leaves, the size of the centimeters is selected in a higher terrain, well-drained place or cultivated with deep furrows and high furrows.

The cultivation of protected areas such as greenhouse plastic greenhouses should pay attention to ventilation and light transmission, cooling and humidity drainage, deep turning of the land, application of sufficient base fertilizer, and increase the application of phosphorus and potassium fertilizer!

The most suitable temperature for downy mildew is 15-17 degrees Celsius, which is spread by air movement, field tillage, watering and insects. When the density of plants in the field is large, the air humidity is high, and the temperature is suitable, the onset of the disease is rapid. Sowing:

50 100 grams of Trichoderma harzianum per 50 kg of seeds, seedling mixing substrate soil: 100 grams of Trichoderma harzianum per cube, seedbed spraying: 5 grams of Trichoderma harzianum per 1 cubic, sprayed once every 5 7 days.

It can prevent the occurrence of diseases.

Adult plants are particularly badly affected. Mainly damage the leaves, first in the lower part of the leaves of the plant appear pale yellow lesions, gradually spread upward, the lesions are nearly round, or polygonal due to the restriction of leaf veins, and then the lesions become brown, dry, severe, the lesions are connected with each other, and the whole leaf is dry and necrotic. Plots with high planting density, excessive use of nitrogen fertilizer, and poor ventilation and light transmission occur.

Therefore, when planting lettuce, it is necessary to control the humidity, nitrogen fertilizer should not be excessive, use more organic fertilizer, keep lettuce plant spacing for ventilation, and also reduce the occurrence of lettuce downy mildew.

In this way, it will attract a lot of small insects, which will make the roots wither very quickly, and there will be mold, spots, and gray on them, so that they will grow very slowly, and they may wither and die.

Its leaves will turn yellow and show signs of wilting, and there are many white spots on the leaves, which will make the whole plant unenergetic, and the disease generally starts from the roots and goes up.

It will cause great harm, and it will also lead to a decrease in the yield of lettuce, and there will also be some mold, and there will also be yellowing of the leaves, and it will also cause a lot of spots on the surface of the lettuce.

Molds and mildew may appear throughout the growth period of lettuce, which can mainly damage the leaves. At first, it is not easy to find, but when he arrives, his lesions will be very large and irregular, and the color will turn yellow-brown, which will directly cause the lettuce to become rotten.

Lettuce downy mildew mainly harms leaves, and can be infected at the seedling stage and adult plant stage. The disease occurs at the seedling stage, and the seedlings turn yellow and die. Leaf infection at the adult stage starts from the lower old leaves or mature leaves of the plant, and gradually expands to the upper leaves, the initial appearance of the disease produces faded green spots, the edge is not obvious, and after expansion, it is polygonal or irregular shaped by the restriction of leaf veins, light yellow, and the size varies from 5 to 20 mm.