What medicine does Chinese cabbage downy mildew hit? What are the main symptoms?

Chinese cabbage downy mildew, commonly known as white mildew, downy leaf disease, etc., is a very common fungal disease in Chinese cabbage planting areas. What are the main symptoms?

Chinese cabbage downy mildew, commonly known as white mildew, downy leaf disease and so on, is mainly harmful to leaves. At first, the gray-white, light yellow or yellowish-green edge of the disease spot appeared on the front of the leaf, and then enlarged into a yellowish-brown spot, which was polygonal or irregular due to the limitation of the leaf vein, and the back of the leaf was dense with white frost mildew. The disease spots are often connected to each other, and the leaves are withered and yellow, so that the local or whole leaves of the diseased leaves die. The disease develops from the outer leaf to the inner leaf, and the diseased plant often dries up layer by layer from the outside to the inside, and the plant can not be covered in severe cases. Or just a small heart leaf ball.

Morbidity regularity

1. Mode of transmission:

In the north, downy mildew overwinters in soil with oospores or hyphae in seed plants. In rainy days or irrigation, it is transmitted to the plant by water splash, and the bud tube is produced after germination, which directly invades the host tissue from the stomata or epidermis, causing the primary infection. Then it develops into hyphae, which spreads in the intercellular space, causing pathological changes in the host tissue, producing cyst peduncles and sporangia from the diseased sites, and sporangia spreading through air flow, causing re-infection and spreading of the disease. The overwintering mycelium of the species can also grow sporangium and sporangium from the inside in the following spring, causing re-infection.

2. Conditions of onset:

The occurrence and prevalence of downy mildew are affected by many environmental factors, but it is most closely related to temperature and humidity. Temperature determines the occurrence and development speed of the disease sooner or later. The optimum temperature for sporangia formation and germination was 7: 13 ℃, the optimum temperature for invading host was 16 ℃, and the optimum temperature for mycelium growth and development was 20: 24 ℃. Therefore, when the temperature is 15-24 ℃ and the temperature difference between day and night is large, it is most conducive to the occurrence and epidemic of the disease. The development of plaque is the fastest when the temperature is above 20 ℃, especially when the temperature is 24-25 ℃.

Main symptoms of downy mildew

Downy mildew will occur in every stage of Chinese cabbage growth, and all parts of the plant will be damaged, but the leaf is the most serious, followed by stem, pedicel and seed pod. In the seedling stage, white downy mildew appeared on the back of the leaves, and there were no obvious symptoms on the front. In severe cases, the leaves and young stems turned yellow and died. In the adult stage, the disease usually starts from the outer leaves, at first, light green or yellowish green spots appear on the front of the leaves, the disease spots gradually expand in the middle of the disease, the color also changes to yellowish or light brown, and the expansion of the disease spots is polygonal or irregular due to the limitation of leaf veins. In the later stage of the disease, the plaque becomes yellow or yellowish brown. Enter the pericardium period, if the environmental conditions are suitable, the disease develops rapidly, the disease spot increases rapidly, the leaves gradually turn yellow and dry from the outside to the inside, and finally there is only one leaf ball, and there will be "white smoke" when the wind blows or pedestrians walk in the field. When the stem and pedicel are infected, the disease part is swollen and curved, which is commonly known as "bibcock". When the seed pod is damaged, the fruit bears little or no seed. White downy mildew grows in all parts of the disease.

Chinese cabbage downy mildew occurred for a long time, and began to occur in the seedling stage. The peak period was from the beginning of September to the end of October, and its occurrence characteristics were as follows:

1. Variety factors

The practice showed that there were significant differences in disease resistance among Chinese cabbage varieties, and the resistance of high stump leaves to thick green type was high.

2. Planting management factors

The plots with early sowing, continuous cropping, high density, low-lying topography, stagnant water, high humidity, poor drainage, early onset, lack of fertilizer and weak growth are conducive to the occurrence of diseases.

3. Climatic factors

The disease is easy to occur in the morning and evening with large temperature difference, foggy re-dew and high relative humidity between sunshine and rain; Rain Water is more, foggy and dewy, and the temperature is higher; the occurrence of downy mildew is related to climatic conditions, variety resistance, cultivation measures and so on. Among them, the climatic condition is the most important.

The occurrence and development of downy mildew of Chinese cabbage is fast, prevention and control should give priority to prevention, chemical control must be carried out in the early stage of the disease, specific measures:

1. Strengthen the management of water and fertilizer

On the basis of sufficient application of organic fertilizer, phosphate fertilizer, potassium fertilizer and other basic fertilizer, topdressing is mainly nitrogen fertilizer, and the amount of urea per mu is generally no more than 30 jin in seedling stage, rosette stage and pericardium stage. Watering should be watered with small water frequently and be drained in time after rain. Rosette stage is mainly to promote growth, timely watering to meet the water needs for its growth.

2. Early seedling, late seedling, moderate squatting seedling

3. Foliar fertilization

Combined with the prevention and control of diseases and insect pests, spraying foliar fertilizer can improve plant disease resistance.

4. Chemical control

The following agents are selected: 69% enoylmorpholine, that is, 20 grams; 68.75% fluorocarb, that is, silver farfarin 30 ml; 30% ether ester, that is, Cuibei 20 ml; 66.5% propionamide, namely Prec, 40 ml; 72% Kangling, 20 grams; 72% grams, 25 grams. The above choice of one agent, plus 30 jin of a sprayer water foliar spray, can be used alternately, the interval of 5 days, even spray 2 times 3 times. During the onset of the disease, special attention should be paid to the use of drugs after rainfall. The agents for the control of downy mildew of Chinese cabbage can also be mixed with permethrin, methamidomide, thiazine, imidacloprid, imidacloprid and foliar fertilizer to treat leaf eating, borer, and whitefly, so as to reduce the number of times of drug use.