It is a fungal disease, which mainly harms the leaves of plants and spreads through wind, airflow and rain.
1. 1 pathogenic conditions
The conditions that can lead to a large-scale outbreak of the disease are heavy soil, low terrain, poor drainage, high air and soil humidity caused by weather and man-made, or small plant spacing, poor ventilation, insufficient light, untimely weeding in intertillage, excessive nitrogen fertilizer and so on. It is the easiest to get sick in the environment of 16~20℃.
1.2 symptoms
If you get sick at seedling stage, the consequences will be that the green of the seedlings will fade and turn yellow, and even worse, they will wither and die; At the initial stage of adult infection, there are nearly round or polygonal lesions on the leaves, which are pale yellow and develop from the lower leaves. When the humidity is high, there is a white mold layer on the diseased spots on the back of leaves, which will further develop to make the diseased spots contiguous and yellowish brown. If the control is not timely, the pathogen will infect the stem, appear black stem, and the stem will die in the later stage.
1.3 control method
The prevention and control of downy mildew should follow the principle of agricultural prevention and control, supplemented by drug prevention and control. Agricultural control should mainly improve the ability of field irrigation and drainage, select disease-resistant seeds, control planting density, timely intertillage and weed control in the middle growth period, improve the permeability between plants, and be beneficial to plant lighting and ventilation. When there is a lot of rain, drainage should be done in time to ensure the appropriate field density.
This is a fungal disease, which is spread by airflow and rain. It mainly harms leaves, and the pathogen can overwinter in the diseased plants until the environment is suitable for the first infection in the following year.
2. 1 pathogenic conditions
The main onset conditions are warm and humid in spring and summer, foggy, rainy and dewy in autumn; When the temperature is high in summer and the air humidity is high, it is easy to cause diseases when the temperature is higher than 20℃ at night. At the same time, insufficient nutrients, weak plant growth, or excessive nitrogen fertilizer and fertilization will also lead to high incidence.
2.2 onset symptoms
At the early stage of the disease, only irregular waterlogged lesions will appear on the surface of the leaves, with a diameter of 2~ 10mm, light brown color, grayish white center, and yellowish brown to dark brown edges. In the later stage, the lesion gradually expanded into a sheet. If the vegetable field is humid, gray mold will grow on the diseased spot until the leaves wither, dry and die.
2.3 Prevention and control methods
First, select disease-resistant varieties on seeds, and then strengthen field management. We must remove diseases in time and bring them out of the field for centralized harmless treatment. We can't leave patients in the wild. Scientific watering and fertilization, watering should be carried out in the morning or in the morning to avoid flooding. In hot and humid weather, it is necessary to apply less or no nitrogen fertilizer and appropriate phosphorus and potassium fertilizer to promote plant growth and improve its disease resistance.
Drug control. Spraying 50% iprodione wettable powder 100 times solution after onset. Amisi can be used to irrigate the roots of seriously ill plots, which can effectively control diseases.
3. 1, pathogenic conditions
The main reasons are as follows: low terrain, continuous cropping in a field, too dense plants in the field, too small spacing between plants, poor ventilation and lighting, poor irrigation and drainage ability, high relative humidity and biased application of nitrogen fertilizer. When the relative humidity is higher than 85% and the temperature is 15~20℃, it is beneficial to the germination of sclerotia, the growth of mycelium and the production of ascomycetes. When the relative humidity in the field is lower than 70%, the incidence and symptoms are obviously reduced.
3.2, symptoms
At the early stage of the disease, waterlogging spots appeared at the base of the stem, and at the later stage of the disease, the spots expanded into brown, and the base of the stem was soft rot or longitudinal crack. When the humidity is too high, dense cotton-wool white hyphae will grow on the surface of the lesion, and then white sclerotia will form. Further development, it becomes a black granular sclerotia in the shape of black rat feces. Eventually, the leaves of the diseased plant will wither until the whole plant dies.
3.3, prevention and control methods
Disease-resistant varieties are preferred. Before sowing, seeds can be treated with seed coating agent or bleached with 10% saline for 2~3 times, which can effectively reduce the carrier rate of seeds. Scientific crop rotation, careful and thorough soil preparation, and centralized treatment of crop stubble outside the field. Reasonable control of field density, improvement of ventilation, ventilation and lighting among plants, timely ditch cleaning and waterlogging prevention in rainy season, and improvement of drainage and drainage capacity are beneficial to reduce field humidity. Balance fertilization, maintain moderate nutrients, and ensure strong plants.
After onset, 50% thiophanate-methyl 500 times solution, 90% carbendazim 800 times solution +750 times solution and 50% nongliling wettable powder 1000 times solution can be sprayed, once a week 1 time, 2~3 times in total. In severe cases, it can be sprayed once every 3 to 5 days.
4. 1, pest characteristics
Adults and nymphs live in groups on the back of leaves, pedicels or tender stems, sucking juice for a living, and secreting honey dew all over leaves, which affects photosynthesis. After the pest occurs, the young leaves will deform and curl downward, and the diameter and pedicel will also bend. At this time, the diseased plants will become shorter and weaker, which will affect the growth of good plants. In severe cases, the plants will wither and die, affecting the yield, and aphids will also spread viral diseases.
4.2, prevention and control methods
Clear weeds in the field and around in time, and protect natural enemies of aphids, such as ladybugs, syrphids, spiders, lacewings, etc. Because of the phototaxis of aphids, it can also be used to trap and kill aphids. Using natural enemies and phototaxis to trap and kill is effective and environmentally friendly, which accords with the development concept of green agriculture. At the early stage of pest occurrence, 1000 times of 50% pirimicarb wettable powder, 3000 times of 10% mirex or 10% duolebao emulsion can be used for control once every 7-8 days for 2-3 times continuously. The use of pesticides must be guaranteed.