How to treat lettuce downy mildew, lettuce downy mildew is very common, how to prevent lettuce downy

This year, lettuce planted in the fields of some vegetable producing areas in Hanchuan City has downy mildew, and a small number of lettuce have stem rot, and the farmers are very anxious and hope for expert help. This newspaper specially invited senior agronomist Yu Hongzhang to support.

Downy mildew is mainly harmful to the leaves, the base of the diseased leaves have yellow lesions, the whole leaves of the serious field lettuce are yellow, the back of the leaves is white mold when wet, and the disease spots are continuous in the later stage, when the weather is dry, the leaves will be brown and dry. Stem rot damages both leaves and petioles, and the leaves are moist and ulcerated with reticulate hyphae. The petioles near the ground have brown necrotic spots, and when the weather is rainy, the brown sap is exposed, and when the climate is dry, the brown spots are concave, with brown sclerotia in between.

Both diseases are fungal invasions, and the bacteria overwinter on the remains of diseased plants or attached to seeds. The main inducing factors are the suitable climate, moderate temperature, high air humidity, and at the same time, the field planted with lettuce is biased with nitrogen fertilizer, so that it grows vigorously, the field shade is large, and the drainage is poor. The invasion route is spread by wind and rain, irrigation or fertilization, and weeding touches the plant, when the plant is injured, the germ is more likely to invade through the wound or stomata.

In early October, the weather was fine in most places in the early stage, and the rainy temperature dropped in the later period, which was conducive to the spread of lettuce disease. The prevention and control methods of lettuce and two diseases are as follows: 1. Select disease-resistant varieties.

For susceptible stubble fields, varieties such as wrinkled leaf lettuce can be used. The leaves of wrinkled leaf lettuce are thick, the young stems are short and thick, late ripening, fertilizer and moisture tolerance, strong disease resistance, high yield and good quality. At the same time, seeds can be soaked in 10% salt water to eliminate germs.

2. Strengthen agricultural prevention and control. In the field where lettuce is planted, the ditch should be thoroughly tidied up, so that it can be drained and irrigated, and water must not be stained; When cultivating and weeding, pay attention not to hurt the roots and leaves; It is necessary to remove yellow, diseased and residual leaves at any time to prevent the spread of infection; Crop rotation should be carried out for more than two years for severely diseased fields; Reduce nitrogen fertilizer and increase phosphorus and potassium. Third, carry out chemical prevention and control.

It can be used with 25% Ruixin mold, methama, wettable powder 600 times liquid, 58% Ruixin manganese zinc (methyl manganese zinc) wettable powder 400 times liquid, 72% Kelu (gram frost cyanide, frosturea manganese zinc) wettable powder 600-700 times liquid, % ethylphosphine aluminum wettable powder 250-300 times liquid, 75% chlorothalonil wettable powder 600 times liquid, 50% carbendazim wettable powder 800 times liquid, 10% sclerotia net wettable powder 500 times liquid, 45% dyceylammonium water solution 900 times liquid, 70% mancozeb wettable powder 400 times liquid, Bordeaux liquid 1:1:250-300 times liquid, etc.

When carrying out chemical control, it is necessary to prevent and control the diseases that occur in the spot pieces in a timely and rapid manner; When the disease has occurred in a large way, spray it 1-2 times with Kelu first, and then use ethylphosphine, manganese zinc, etc. for prevention and control, and the effect is better.

Choose disease-resistant varieties, choose varieties such as lettuce with wried leaves, and soak seeds in 10% salt water. Strengthen agricultural prevention and control to remove diseased leaves, and carry out crop rotation for more than two years; Reduce nitrogen fertilizer and increase phosphorus and potassium. Chemical control of 72% gram dew wettable powder 600-700 times liquid.

In severe cases, spray 1-2 times with Kelu first, and then use ethylphosphon, manganese zinc for prevention.

First, choose disease-resistant varieties. 2. Cultivate disease-free and strong seedlings. 3. Strengthen the management of fertilizer and water in the field, increase the application of phosphorus and potassium fertilizers, remove diseased plants and leaves, and clean the countryside.

Fourth, in the early stage of the disease, the prevention and treatment of pesticides should be carried out, and fluoxamide, downy mildew carb hydrochloride, enoylmorpholine, pyraclostrobin and other agents should be used alternately, with an interval of 7 10 foliar sprays.

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.

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.

1. The germs of lettuce black spot disease usually appear in the diseased residues in the soil, so that they can survive the winter safely. Generally, in rainy and humid weather, it is more likely to be attacked by black spot disease, and once it occurs, it is relatively harmful to lettuce. In an environment with suitable temperature and humidity, lettuce black spot disease can easily produce spores for infectation, and then spread through wind and rain.

Especially when the soil fertility is not enough, or the lettuce grows slowly and weakly, it is easy to suffer from black spot disease.

2. To prevent and control lettuce black spot disease, it is mainly necessary for growers to strengthen field management. When topdressing, choose organic fertilizer and phosphorus and potassium fertilizer, so as to improve the disease resistance of lettuce.

3. In addition, lettuce selection is also very crucial, and it is generally necessary to choose excellent varieties with no disease and strong adaptability. The seeds can be treated before sowing to improve the resistance of lettuce to diseases. Of course, the soil in which the lettuce is planted is also very important, and it is necessary to rotate the crop.

Generally, spraying antibacterial pesticides can be prevented, you should go to the nearby agricultural materials (pesticides) store to consult directly, even if someone tells you what pesticides to use on the Internet, you can't buy them nearby, it is also in vain, and online shopping is time-consuming, right?

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.