Lettuce downy mildew is a bacterial disease, how to prevent lettuce downy mildew?

The lesions are yellowish-green at first, with no distinct margins, and then enlarge, polygonal due to venous limitations. When wet, white mold grows on the back of the leaf, sometimes spreading to the front of the leaf. The disease usually starts in the lower leaves of the plant and gradually spreads upwards.

In the later stages, the lesions die, turn yellowish-brown and join into fragments, causing the whole leaf to dry up. Pathogens overwinter in soils with diseased residues and are transmitted by wind, rain, and insects. The optimal onset temperature is 1 19, the most suitable temperature is 15 17, the relative humidity is above 90%, and the most suitable susceptible growth period is the adult stage.

The incubation period of onset is 3-5 days. The incidence is severe in years with low temperature and rainfall and large temperature difference between day and night; Rainy and foggy autumn, the condition is serious. The disease is more serious in fields with continuous cropping, low terrain and poor drainage, as well as fields with too dense tillage, poor ventilation and light transmission, and excessive fertilizer and water application.

Deep ditch and high furrow, reasonable dense planting. Control moisture, remove stains, and apply phosphorus, potassium, calcium and foliar fertilizers scientifically. Promptly uproot diseased plants and clean up rural areas.

Symptoms and patterns of occurrence. Mainly harmful to leaves. At the seedling stage, the affected stems and leaves rot in water.

Adult plants begin to grow from leaves close to the ground, with drought and flooding, irregular spots, and then expanding into brown. The base of the diseased leaves is reddish-brown and varies in shape and size. The shape of the base of the stem is similar to that of the base of the petiole.

In severe cases, it ulcerates from the base upwards, the stems and leaves of the aboveground parts wither, and the whole plant dies. In a humid environment, a gray-brown or gray-green mold layer develops in the affected area. When the weather is dry, the diseased plants gradually dry up and die, and the mold layer turns from white to gray to green.

The flower organs or flower stalks are damaged and rot in the form of water stains.

The pathogen overwinters in soil with diseased residues, spreading through air currents. Low temperature and high humidity environment is easy to occur, the most suitable temperature for the onset of the disease is 20 25, and the relative humidity is above 94%. Seedlings are the most susceptible disease.

Plants are weak or affected by low temperatures. Seizures are more likely to get sick. Fields that are too densely cultivated, too low in temperature, too high in humidity, poor in light, and poorly ventilated are seriously ill.

In winter and spring, the incidence is higher in years with low temperatures and rainfall. Choose healthy plants to keep their seeds. Promptly dispose of the sick and disabled, and clean up the rural areas.

Strengthen management, increase ventilation, reduce humidity, and remove stains. Scientific fertilization, appropriate increase of phosphorus and potassium fertilizer. Block the wind and remove moisture in time.

Reasonable watering, frequent watering, less watering, less flooding. Chemical control.

In severe cases, it can spread to the front of the leaves and grow white mold. In later stages, the lesions turn yellowish-brown. In severe cases, most of the lesions are connected together, the leaves are yellow, and finally the surface of the stem turns brownish-black, or even the whole plant rots.

The optimal temperature for the disease is 15-17 and can occur from 1-19, while low temperature and high humidity are most likely to occur at the beginning of winter or at the end of rainy spring. At the same time, lettuce grows in large quantities in autumn and winter, and due to poor ventilation and weak light, it is easy to cause a high incidence of the disease. At the same time, improper field management, such as premature overwatering, wet or poor soil drainage, and excessive nitrogen fertilizer application, can also easily cause aggravation of the disease.

Agricultural control: (1) Select disease-resistant varieties according to local conditions. Generally, the roots, stems, and leaves are purplish-red or dark green varieties that are more resistant to disease.

2) Implement crop rotation. Severely diseased fields should be rotated with non-Asteraceae vegetables for more than 3 years to reduce field pathogens**. (3) Strengthen cultivation management.

When seedlings are divided and planted, diseased plants are eliminated. Reasonable dense planting, diligent cultivation, more loose soil, strengthen wind and humidity reduction, scientific watering, pay attention to drainage, timely lower diseased and residual leaves, and appropriately increase phosphorus and potassium fertilizer.

At this time, it is necessary to reduce the amount of watering, spray pesticides in time, and increase the light time, so that you can effectively prevent and control downy mildew of lettuce.

1. Choose plots with non-Asteraceae vegetable stubble, and seriously diseased plots should be rotated with other non-Asteraceae vegetables for more than 2 or 3 years, and the diseased and residual bodies should be removed from the field or shed after harvest to reduce the source of bacteria.

2. The planting density should be reasonable, avoid excessive density, canopy in the plant, which is not conducive to ventilation and dampness, and the cultivation management in the shed should be scientific, and less watering or irrigation under the film. The implementation of high ridge cultivation, full mulch film covering, the base fertilizer should be used with nitrogen, phosphorus, potassium fertilizer, and more organic fertilizer, which can improve the disease resistance of plants.

3. Before sowing, Fumei double seed dressing or methyl frost seed dressing can be used to kill the pathogens on the surface of the seeds and reduce the source of infection. In the early stage of the disease, timely drug prevention and control should be carried out to control the spread of germs.

The main symptoms are manifested on the leaves; In the early stage of downy mildew in lettuce, there will be light yellow irregular spots on the lettuce leaves, and white frost cuticle can be seen on the back. If not treated in time, it will progress into brownish-yellow patches, the patches overlap, the leaves will wither and wilt, and 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.

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 yellowish near-round or polygonal angular spots on the leaves, centimeters in size. Factors such as continuous cropping, too dense planting, too much watering, too high humidity in the field, application of unrotted manure or excessive application of fertilizer may lead to the occurrence of diseases, so the prevention and control of these two diseases should start from the aspects of reducing the initial infection, strengthening cultivation management and timely use of fungicides.

With the diseased residues spent in the soil or in the seeds with mycelium, or on the autumn sowing lettuce, the infection is at the beginning of the next season**, and the sporangia are produced the following spring. It is transmitted by wind and rain and insects, and after contact with the host, it mainly invades from the host's epidermis or stomata, and can be repeatedly infected. Pay attention to ventilation and drying, and remove diseased leaves and yellow dead leaves in time.

At the onset of the disease, timely medication can be sprayed with 28% gray mold wettable powder 500 times, 65% chlorine wettable powder 700 times, 75% good speed clean wettable powder 700 times. Once every five days or so, 3-4 times in a row.

During the growth period, every other month and after the flood, the pods should be drenched with medicine to eliminate the source of the disease. Ingredients: Dixone 100g + Potassium Permanganate 50g + Genbao 50ml + Water 50kg Fludioxonil 100ml + Potassium Permanganate 50g + Genbao 50ml + Water 50kg.

First of all, when planting, we must choose the soil is relatively fertile and broad, in the process of fertilization, we must choose farmhouse fertilizer, do not use the fertilizer bought outside, we must often water the plants more, if there is a occurrence of insect pests, then we must spray insecticides in time.

You can spray some insecticides on his roots to remove some insect pests on the surface, or remove some branches that have been diseased, and give them fertilizer and watering to alleviate them, if it is more serious, you can go to some plant experts to spray.

Strengthen management: reasonable dense planting, reasonable fertilizer and water, enhance field ventilation and light transmission, ditch drainage, reduce field humidity, promote plant robustness, and improve plant disease resistance; After harvesting, remove the diseased residues, take them out of the field for centralized destruction, and turn the soil deeply to accelerate the decay and decomposition of the diseased residues.

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.

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.

The effect of carbendazim is not ideal, and the white mold layer of lettuce is generally downy mildew. There is also powdery white that is less common. Downy mildew is a disease that infects quickly and is harmful, and if not prevented and controlled in time, it will lead to damage to functional leaves, and severe limb weight will lead to serious crop yield reduction.

High density, poor ventilation, excessive humidity, long growth, and internal canopy of crops are prone to diseases, especially high humidity and poor ventilation. Attention should be paid to prevention: improve the cavity with strong ventilation and humidity reduction, keep the moisture reasonable, and promote the growth of growth in a timely manner.