How downy mildew is formed, and how to treat downy mildew

Downy mildew is a plant disease caused by downy mildew in fungi. Downy mildew is an obligate parasite, and a very small number of downy mildew can be artificially cultivated, such as Posa digitaria which causes millet white disease, and parasitic downy mildew that causes downy mildew of cabbage. Downy mildew generally starts from the lower leaves, produces light green water-stained dots in the early stage, the edge of the lesion is not obvious, and develops into yellow irregular lesions in the later stage, and the gray-white mold layer is produced on the back of the leaf when the humidity is high, and gradually turns dark gray.

Downy mildew overwinters in soil, diseased residues or seeds with oospores (e.g., millet white disease), or mycelium overwinters in stems, buds (e.g., grape downy mildew) or seeds (e.g., cabbage downy mildew), becoming the primary source of infection in the following year, and re-infecting by sporangia during the growing season. Downy mildew is an obligate parasite, and spinach downy mildew can only infect spinach.

Downy mildew is caused by a fungus infestation of the subphylum Flagellium Pseudodowny mildew Cuba. The gray-black mold layer growing on the lesions is the sporangia and sporangia of the pathogen. The fungus overwinters or summers with the diseased leaves, and can also be used for overwintering on cucumbers, melons and other melon crops.

When conditions are suitable, the fungus produces sporangia that are spread by air currents and rainwater, and invade leaves by stomata or directly through the epidermis, forming a primary infection. After the onset of the disease, the sporangia drift and spread, and re-infection is carried out. Since melons and vegetables can be produced annually, pathogens can also be infected and spread annually due to suitable conditions such as temperature and humidity.

(1) Symptoms Downy mildew, commonly known as black hair, is an important disease in the growth of melons and vegetables. It is mainly harmful to leaves, and at the beginning of the disease, water-soaked yellow spots first appear on the leaves, and after the lesions gradually expand, they become yellow-brown irregular polygonal lesions limited by leaf veins. Under damp conditions, there is a grayish-black mold layer on the back of the lesion.

The disease generally develops from the lower leaves to the upper leaves, and when the disease is severe, the lesions are connected into patches, so that the leaves turn yellow and dry, and are easy to break, and the plants in the diseased field are yellow, like fire.

2) Onset conditions When the temperature is 15 22 and the relative humidity is greater than 83%, it is easy to get sick. If there are water droplets and water film on the leaf surface for 2 to 6 hours, the pathogen is very easy to infect the leaves, and it is easy to get sick in rainy, foggy and dewy weather.

3) prevention and control methods to select disease-resistant varieties, choose fertile sandy loam soil for cultivation, apply foot fertilizer, especially potassium fertilizer, flood irrigation is strictly prohibited during the melon bearing period, timely pruning, pruning, and good ventilation. Spray foliar fertilizer on poor growth seedlings. Downy mildew spreads through airflow, the onset of the disease is rapid, the spray must be timely, generally 5 days before the onset of the disease 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.

I'll illustrate it to you with cucumber as an example!

The cucumber downy mildew fungus is called "Cuban downy mildew", which overwinters or summers on the diseased leaves of southern cucumbers; In the northern regions, where cucumbers are not grown in winter, the monsoon winds blow the robes away from the neighboring areas. The gown sac is produced in large quantities at a temperature of 15-20 degrees and the air humidity is higher than 83%, and the higher the humidity, the more gown sacs are produced.

Experiments have proved that the night temperature drops from 20 degrees to 12 degrees, and the leaves have water for 6 hours, or the night temperature drops from 20 degrees to 10 degrees, and the leaves have water for 12 hours, and the bacteria can complete germination and pouring.

The average daily temperature is 15-16 degrees, and the incubation period is 5 days; 17-18 degree incubation period 4 days; The incubation period of 20-25 degrees is 3 days. The average temperature at the beginning of the field is 15-16 degrees, and the epidemic temperature is 20-24 degrees. Incidence below 15 degrees or above 30 degrees is suppressed.

The temperature difference of 10 degrees is the most conducive to the infection, expansion and reproduction of pathogenic bacteria, and the temperature of 20-35 degrees and high humidity for 2 hours are enough to lead to the occurrence of cucumber downy mildew.

Different plants have different temperature and humidity requirements for downy mildew, but they are not much worse. Carob downy mildew is generally a high incidence period of 20-24 degrees Celsius in the rainy season.

This text is from a hand-typed and is not copied from the Internet.

Downy mildew refers to a plant disease caused by downy mildew in the fungus. Downy mildew is an obligate parasitic probiotic, and a very small number of downy mildew can be artificially cultivated, such as the grassy finger stem fungus that causes millet white disease, and the parasitic downy mildew that causes cabbage downy mildew.

Summary. Hello, thank you very much for your trust, downy mildew is a disease caused by downy mildew in the fungus, belongs to a kind of obligate parasite, downy mildew mainly infects and harms the leaves of crops, from the seedling stage to the adult stage, it is possible to be infected with the disease, in the early stage of the disease, there will be yellow or light yellow nearly round in the upper part of the leaf, polygonal lesions, the back of the leaf appears frosty mildew layer when wet, with the aggravation of the disease, the lesions die in pieces, and in severe cases, all the external leaves can be yellowed and died, at a lower temperature, Under the weather conditions with high humidity, it is most likely to occur, generally causing a reduction of crop yield of about 20% to 40%, and the spread of double mold bacteria is fast, which can be spread through air flow, watering, agricultural operations and insects, etc., and the bacteria can germinate and spread quickly between 6 and 17 degrees.

Hello, thank you very much for your trust, downy mildew is a disease caused by downy mildew in the fungus, belongs to a kind of obligate parasite, downy mildew mainly infects and harms the leaves of crops, from the seedling stage to the adult stage, it is possible to be infected with the disease, in the early stage of the disease, there will be yellow or light yellow nearly round in the upper part of the leaf, polygonal lesions, the back of the leaf appears frosty mildew layer when wet, with the aggravation of the disease, the lesions die in succession, and in severe cases, it can cause all the external leaves to wither and die, at a lower temperature, In the weather conditions with high humidity, it is most likely to occur in the state type, which can generally cause a crop yield reduction of about 20% to 40%, and the spread of double mold germs is fast, which can be spread through air currents, watering, agricultural operations and insects, etc., and the germs can germinate and spread quickly between 6 and 17 degrees.

I'm still a little confused, can you be more detailed?

Downy mildew is mainly prevention, and you can ask any questions.

<> downy mildew can be sprayed with 500 times of 75% chlorothalonil wettable powder at the beginning of the disease, and 58% methyl frost and manganese zinc wettable powder 500 times or 69% enoyl manganese zinc wettable powder 800 times liquid spray can be used to spray once every 7 days, and continuously control 2-3 times, which can effectively control the spread of downy mildew. At the same time, it can also be combined with spraying foliar fertilizer and plant growth regulators for control, and the effect is better.

**The specific drugs for downy mildew are: dimetalline, chlorobromoisocyanuric acid, enoylmorpholine, and cyanide.

1. Oxazole: Oxazomethoxine is a new generation of nongxiao Tongxi medicine fungicide, and is also a systemic fungicide and soil disinfectant, which has a unique mechanism of action, which can effectively inhibit the germination of spores and the normal growth of pathogenic fungal mycelium or directly kill pathogens, and the efficacy can reach two weeks.

2. Chlorbromoisocyanuric acid: Chlorobromoisocyanuric acid spraying on the surface of crops can slowly release hypobromoic acid (HOBR) and hypochlorous acid (HOCL), the activity of hypobromide is four times that of hypochlorous acid, and it has a strong ability to kill bacteria and fungi.

3. Pre-fernoylmorpholine: Enoylmorpholine is a morpholine fungicide, which is mainly used to control downy mildew and late blight on grapes and other fruit trees.

4. Cyanide in Frost Urea: Cyanide in Frost is a high-efficiency and low-toxicity fungicide. Cyanide is widely mixed with other protective fungicides, which can be used for cucumbers, grapes, tomatoes, lychees, giant vegetables and other vegetables, and is effective against downy mildew.

The leaves are damaged, and the leaf surface appears light yellow irregular, oily spots, which are yellow-brown and have inconspicuous polygonal spots after enlargement, and when the environment is humid, the diseased spots produce a layer of white frosty mold on the back of the leaves.

Viticultural techniques.

1. When planting, you should choose a plot with sufficient light and high calories, which is more conducive to the accumulation of sugar.

2. The planting time can be carried out between January and May, and the method is relatively simple. Dig a pit directly on the plot, plant the seedlings in, and water them after planting.

3. Equal growth to a certain height in time to erect a frame, and reasonable fertilization and management. Fertilization can choose safe and hormone-free water-soluble fertile leaf water-soluble fertilizer, which can improve the immune resistance of grapes and reduce the occurrence of diseases.

The disease can occur at all stages from seedling to harvest, and adult plants are more affected. It is mainly harmful to the leaves, which develop from the base to the upper leaves. In the early stage of the disease, light yellow near-round to polygonal lesions are formed on the leaf surface, which is easy to be complicated by horn spot disease, and a frosty mold layer is produced on the back of the leaf when the air is humid, which can sometimes spread to the leaf surface.

In the later stage, the lesions die and die, yellowish-brown, and in severe cases, all the outer leaves wither and die, similar to Verticillium wilt.

The route of transmission and the conditions of the disease are here: the pathogen overwinters on seeds or lettuce in autumn and winter, or oospores overwinter on diseased residues. It spreads mainly through air currents, watering, farming and insects.

The germination temperature of pathogen spores is 6 10 and the suitable infection temperature is 15 17, and it is easy to develop diseases such as field planting with dense forest, too early watering after planting, too large, high soil moisture, and poor drainage. Continuous rainy weather in spring and early summer or autumn is most likely to occur, and when the disease is severe, it can cause 20% to 40% yield loss.