Speaking of powdery mildew, I must be familiar with everyone. From Daejeon to the greenhouse, from the vegetable garden to the orchard, it can be said that there are crops, and most of them have their presence. The disease develops rapidly, the roots are difficult to remove, and the damage to crops is great!
At the turn of the spring and summer, the temperature rises rapidly, the temperature difference between day and night is large, and the dry and wet changes in the cultivation environment are frequent, which is very conducive to the occurrence of powdery mildew, so we must pay close attention to preventive work.
Various powdery mildew
Wheat powdery mildew
The occurrence period of wheat powdery mildew is long, and the initial flowering period is its main period. It can occur and endangered in the middle and late stages of wheat filling. The occurrence of serious diseases or cloudy and rainy days is conducive to the occurrence of powdery mildew.
Melon powdery mildew
From the seedling stage to the harvest period, the disease can be affected, mainly affecting the leaves, petiole and stem vines, and generally does not infect melon strips. Mainly from mid-April to late June, autumn planting cucumbers also occurred from late September to mid-11.
Strawberry powdery mildew
Mainly harmful to leaves, petioles, flowers, pedicels and fruits. Continuous cropping, failure to remove old leaves and diseased leaves, partial application of nitrogen fertilizer, plant greening, planting too dense or improper ventilation and dehumidification, are easy to induce strawberry powdery mildew, and the incidence is heavy. The onset of the disease is from late February to early May, and from late October to December.
Grape powdery mildew
It mainly harms young organs such as leaves, new shoots and fruits, and the old leaves and colored fruits are less affected. It is easy to develop when the wet and dry alternate, ventilation and light transmission conditions are poor. After flowering to the young fruit stage, before and after the fall is the peak period of incidence.
Apple powdery mildew
It mainly damages the young shoots and young leaves of apple trees, and can also be harmful buds, flowers and young fruits. April to June is the main hazard period. During the hot season from July to August, the disease stagnation, and at the end of August, it spread again on the autumn shoots.
Bean powdery mildew
It mainly harms the leaves and can also invade stems and pods. It happens from May to November.
Solanum powdery mildew
It is mainly harmful to the leaves. In the initial stage, round white powdery mildew spots grow on the front or back of the leaves. In the later stage, the whole leaves are covered with white powder, and then turn into grayish white. Relatively speaking, the onset of the back of the leaves is heavier. June to October is the main hazard period.
Hazard characteristics
Strong parasitic ability
Powdery mildew is an obligate parasite with strong parasitic ability. After the germination of mycelium or conidia, it is not necessary to take the wound, and it can penetrate into the epidermis of the host organ through the stomata or directly. The thinner and tenderer the organ of the host plant, the higher the incidence and the degree of damage to powdery mildew.
Developed conidia
The conidia of powdery mildew pathogens are particularly developed, and most of them are distributed outside the epidermis of the infected part. When the temperature, humidity and nutrient conditions are suitable, the conidia and hyphae germinate to form the germ tube and invade into the host epidermal cells. Forming a nutrient that absorbs the host cells. Therefore, the powdery mildew pathogen is most distributed near the epidermal layer of the host plant, while the number of deep pathogens in the affected part is small.
Conidia formation and germination have different environmental requirements
Powder disease requires higher temperatures and relative humidity when forming conidia. Lower germination requires lower relative humidity. Therefore, the sweltering weather after a rainy day or a large temperature difference between day and night is conducive to the occurrence and prevalence of powdery mildew.
In addition, when cultivated in protected areas, the light is weak, the ventilation is poor, and the relative humidity of the air is too large, especially if the trimming is unreasonable, and powdery mildew often occurs more seriously.
Prevention and control difficulties
The treatment time is too late
In the early stage of powdery mildew, that is, when the white powder spots on the leaves are 1~3 mm, it is necessary to keep up with the drug treatment. Once the lesions are enlarged, on the one hand, a large number of white powder spores have matured, which will cause rapid spread. It is the nutrition of the cells in the leaves that have been drained by the white powder spores, and the disease resistance is greatly reduced. When the lesion is enlarged or a large area is outbreak, it is blocked by a large number of leaves, and the medicament is difficult to spray evenly, and the control is difficult.
Continuous use of a single agent
The powdery mildew pathogen is easy to produce resistance, and many farmers' drugs for controlling powdery mildew are very simple, and often one drug is used multiple times, so that the resistance of the bacteria is only stronger.
Multi-faceted integrated prevention
Under suitable conditions, powdery mildew has a large amount of reproduction and is widely distributed and difficult to stop. Therefore, the prevention and treatment of pharmaceuticals should be early, and at the same time, before the onset of the disease, it is necessary to create an environment that is not conducive to the development of powdery mildew by strengthening cultivation management such as rational water and fertilizer, timely pruning, and improvement of ventilation and light transmission. In the case of powdery mildew in the protective land, in addition to spraying, fumigation can be combined to control the greenhouse degree to alleviate the spread of the disease.
Easy to be confused with downy mildew
Powdery mildew is very similar to downy mildew and is confusing. Powdery mildew begins with small pink spots, which in turn extend to half of the leaves and even the entire leaves. The powder is sometimes felt-like, causing defoliation, while downy mildew is mostly restricted by veins, and the mildew is thin and thin, and the leaves are rolled and leaves. Withered yellow, not falling. Pay attention to identification, the right medicine.
Integrated prevention
Agricultural control
1Select disease-resistant varieties : There is a difference in tolerance to powdery mildew between varieties, so we must first choose resistant varieties.
2 Improve the ventilation and light transmission conditions: the planting density is suitable, and the old leaves at the bottom are destroyed in time, which is good for the wind and light in the field. Clean the garden, remove the diseased leaves, sickness, and residual branches, and clear them out of the field to concentrate or burn them. It should strengthen the release of wind, reduce humidity, scientific watering, and create an environment that is not conducive to the development of powdery mildew.
3 Balanced fertilization : increase the application of organic fertilizer , phosphorus, potassium fertilizer, to avoid excessive growth due to excessive nitrogen fertilizer. The thin and tender skin is more susceptible to the infection of powdery mildew. In the rapid growth stage of crops, in addition to paying attention to soil balanced fertilization, combined with the application of sea snail bio-stimulants, foliar spraying of phosphorus and potassium source pool can help accelerate young children. The old organs are ripe, regulate crop nutrition, and improve the disease resistance of plants.
Chemical control
1 Prevention and control as early as possible : powdery mildew colonies can germinate and invade on the leaves, and the mycelium can grow on the surface of the leaves on one day, and the lesions of white hyphae in the infestation on the 5th day, and the lesions are matured and produced in 7 days. Shengzizi scattered and spread. At this time, the number of germs is fast, and the disease is also popular. Therefore, it is very important to prevent and control at the beginning of the disease.
The occurrence of disease is often the accumulation process of the number of bacteria that accompany the growth of the crop. Therefore, measures are taken at the beginning of each growing season to keep the number of germs at a minimum, even in the period of powdery mildew, it is not too difficult to control. Waiting until powdery mildew has broken out and looking for so-called special effects drugs is the most stupid coping strategy.
2 Choose the right agent : According to the characteristics of plant growth characteristics and disease occurrence stage, choose the appropriate fungicide .
Stone sulphur mixture, methyl thiophanate, mancozeb, etc., are mainly used for pre-morbid protection, and have almost no therapeutic effect on powdery mildew. At the same time, sulfur preparations are sensitive to many vegetables and fruits and cannot be used.
Difenoconazole, myclobutanil, propiconazole, etc., have good preventive and therapeutic effects on powdery mildew, but also consider the safety of these agents on plants and the resistance to disease.
Esterase, trifloxystrobin, etc., the mechanism of action is unique, the site of action is more, and the treatment of powdery mildew is higher. However, such fungicides are particularly prone to drug resistance, and the effect has been reduced, while the cost of imported drugs is relatively high.
3 increase the amount of water spray : the conidia of powdery mildew has high water content, and when the humidity is high, it is easy to absorb water and rupture and die. Therefore, spraying at low concentration and large water volume will spray all the leaves, which will have better control effect. However, it should be noted that if the relative humidity in the shed is high, increasing the amount of water spray may cause other diseases.
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