What are the symptoms of powdery mildew on flowers, fruit trees, wheat and other crops, and what is the best medicine to spray?

Powdery mildew is one of the main diseases on summer vegetables. In summer, high temperatures, muggy and humid conditions, improper fertilization, spindly plant growth, and poor ventilation easily cause this disease to occur.So what medicine is better for powdery mildew? What symptoms are there?

Powdery mildew mostly occurs in the late stage of plant growth, mainly harming leaves, and can also harm leaf stems and stems. June to July is the peak period of the disease for cucurbits, especially cucumbers, melons, watermelons and other cucurbit crops.

Generally speaking, the powdery mildew pathogens on different plants belong to different genera. Most powdery mildew pathogens can only infect one host plant, and only a few powdery mildew pathogens can infect multiple host plants. But no matter which genus it is, the diseases caused are very similar in their basic symptoms.

Detailed explanation of powdery mildew on various crops:

1. Cucurbit powdery mildew

Powdery mildew is one of the common diseases of cucurbits. Because in recent years the powdery mildew pathogen has developed some resistance to pesticides, and it can occur in all four seasons, control has become somewhat difficult. In ordinary years, yield loss is about 10%, and in epidemic years, yield loss is about 20%-40%.

It can be infected from the seedling stage to the harvest stage, mainly harming leaves, followed by petioles and stems and vines. It generally does not infect the fruit. When leaves are infected, small round white powdery spots first appear on the back or front of the leaves, and later gradually expand into irregular powdery mildew spots with indistinct edges. As the disease develops, the spots join together and cover the entire leaf, and the affected parts show chlorosis and yellowing. In the late stage of the disease, many dark brown small black dots appear on the spots. Finally, the white powdery mold layer ages and turns grayish white. When the disease is severe, the diseased leaf tissue turns yellowish brown and dies. Under high humidity conditions, the pathogen can also infect stems and vines and flower organs, producing white powdery spots with symptoms similar to those on leaves, but the spots are smaller.

The peak period of cucurbit powdery mildew is mainly from early to mid-April to late June. When harming cucumbers in protected cultivation, there is also a risk of occurrence in autumn-planted cucumbers from late September to early to mid-November. The most suitable climatic conditions for the disease are a temperature of 16-25°C and a relative humidity above 80%. For cucumbers grown in protected cultivation, the disease is more severe because of poor ventilation, excessively high planting density, excessive application of nitrogen fertilizer, and low-lying fields.

[Control methods]

(1) Select disease-tolerant varieties.

(2) Strengthen management. Plant at a reasonable density, dig ditches for drainage; promptly remove diseased leaves and old leaves; strengthen ventilation and light penetration to enhance plant growth.

(3) Chemical control. Spray promptly at the early stage of the disease, once every 7-10 days, for 2-3 consecutive treatments, and note to alternate the products. The pesticides can be 80% jinyimi.myclobutanil wettable powder at 2500 times, or 40% flusilazole at 4000 times, or 25% ethirimol suspension concentrate at 1500 times, or 37% difenoconazole at 1500 times for spray control.

2. Strawberry powdery mildew

Strawberry powdery mildew is one of the important diseases of strawberry. It can occur throughout the entire strawberry growing season. Infection at the seedling stage causes a decline in seedling quality, making survival after transplanting difficult; infection of the fruit seriously affects strawberry quality and leads to a decrease in the proportion of marketable fruit. Under suitable conditions, it can develop rapidly, spread into a disaster, and cause serious losses.

Strawberry powdery mildew mainly harms leaves, petioles, flowers, flower stalks and fruit. When leaves are infected, a thin layer of white mycelium grows on the back of the leaves at the early stage of the disease. As the disease worsens, the leaves curl upward into a spoon shape and produce dark stains of varying sizes. Later, the spots gradually expand and produce a thin frost-like white powdery substance on the back of the leaves. When the disease is severe, multiple spots join together and can cover the entire leaf; in the later stage, reddish-brown spots appear, and the leaf margins shrink and scorch. When flower buds and flowers are infected, the petals turn pink and the flower buds cannot open. When fruit is infected, young fruit cannot expand normally and dries up; if infected in the later stage, the fruit surface is covered with a layer of white powder. As the disease worsens, the fruit loses its luster and hardens, coloring becomes poor, the quality of the berries is seriously affected, and they lose their commercial value.

The optimum temperature for pathogen infection is 15-25°C, with relative humidity above 80%. In protected strawberry cultivation, the annual peak periods of powdery mildew are from late February to early May and from late October to December. The sensitive growth stages for strawberry infection are from fruit setting to the late harvest stage, and the incubation period of the disease is 5-10 days. Strawberries in protected cultivation become diseased earlier than those in open-field cultivation, have a longer damage period, and suffer more severe damage. Excessive planting density, extensive management, poor ventilation and light penetration, and weak plant growth easily lead to worsened occurrence of powdery mildew. During strawberry growth, when high temperature and drought alternate with high temperature and high humidity, the disease worsens.

[Control methods]

(1) Select disease-resistant varieties and cultivate disease-free strong seedlings. Different strawberry varieties differ greatly in resistance to powdery mildew.

(2) Strengthen cultivation management. Clean the seedling field before planting and after planting; during strawberry growth, promptly remove diseased, old and residual leaves and diseased fruit, and destroy them centrally; maintain good ventilation and light penetration conditions, drain promptly after rain, strengthen fertilizer and water management, and apply more Jiamei Hongli, Jiamei Hailibao and Yinglilai to cultivate robust plants.

(3) Chemical control. For open-field strawberries, the flower stem elongation stage before flowering, and for protected cultivation, October-November and March-May of the following spring, are the key prevention periods. At the early stage of the disease, use Bayer Luna Sensation, ethirimol sulfamate, Dow AgroSciences Karathane (36% dinocap emulsifiable concentrate), Peru Keruimu, difenoconazole, tebuconazole and others alternately for control. Spray mainly on the disease center and around it, once every 7-10 days, for 2-3 consecutive treatments.

3. Grape powdery mildew

Grape powdery mildew occurs relatively commonly, and in epidemic years it often causes great losses to fruit quality and yield. It also affects the growth and development of the canes and the growth of the grape in the second year.

The powdery mildew pathogen can infect all green tissues of the grape. When leaves are damaged, chlorotic patches of varying sizes appear, after which a white powdery substance is produced covering the spots. In the later stage, the leaf surface under the powdery spots shows brown patterns, and in severe cases the leaves scorch and fall off. Sometimes small black grains are produced on the diseased parts. After young leaves are infected, they often shrink and twist and develop slowly. After the rachis is infected, the tissue becomes brittle and breaks easily.

When young fruit is infected, the fruit surface is covered with white powder, and the berries tend to wither and drop off. On some fruit surfaces, dark brown net-like patterns appear. Diseased fruit stops growing, becomes deformed, the flesh texture hardens, and the taste turns sour, and the berries crack easily and cause rot.

The peak of the disease is after grape flowering and during the young fruit stage. Hot and humid muggy weather is most likely to cause the disease, and it spreads very quickly on foggy nights. Continuous rain, or truly high temperatures, will suppress the epidemic and occurrence of the disease. If pesticide use before bagging the fruit clusters is not strict, the fruit at maturity will crack due to powdery mildew infection.

[Control methods]

(1) Thoroughly clean the orchard. During winter pruning, burn the cut diseased canes and residual leaves. Before budding, use 3-5 degree lime sulfur mixture; keep good ventilation and light penetration on the trellis; promptly remove the disease center plants, diseased shoot tips and diseased fruit clusters, and bag the young fruit in time.

(2) 80% jinyimi.myclobutanil wettable powder has a special effect on this disease. At the early stage of the disease, 80% jinyimi.myclobutanil, or azoxystrobin, or myclobutanil can be sprayed for control, and the application time should avoid high temperatures.

4. Eggplant powdery mildew

Eggplant powdery mildew is one of the common diseases of eggplant, and it occurs in all vegetable-growing areas. It can occur and cause damage in both open-field cultivation and protected cultivation, but protected cultivation is clearly more severe than open-field cultivation. In years with warm weather and much rain during the growing period, the disease is severe. When the disease is severe, both sides of the leaves are completely covered with white powder.

Eggplant powdery mildew mainly harms leaves. At the early stage of the disease, irregular chlorotic yellow small spots appear on the leaf surface, and white small mold spots appear on the corresponding part of the leaf back. Later, the number of spots increases, and the white powdery substance becomes increasingly obvious and forms white powdery spots. The white powdery spots can join with each other, and after expansion cover the entire leaf surface. In severe cases, both sides of the leaves are completely covered with white powder, finally causing the leaves to turn yellow and dry up.

The most suitable climatic conditions for eggplant powdery mildew are a temperature of 16-24°C and relative humidity of 45-75%; when relative humidity exceeds 95%, the development of the disease is inhibited. The sensitive growth stage for eggplant infection is the flowering and fruiting stage. Fields that are low-lying, poorly drained, have poor crop growth, are continuously cropped, are planted too densely in cultivation, have poor ventilation and light penetration, and receive excessive nitrogen fertilizer have severe disease. Among years, those with warm springs and summers and much rain have severe disease.

[Control methods]

(1) Agricultural control. Practice crop rotation; select disease-resistant varieties; fertilize scientifically to enhance the plant's disease resistance and stress resistance; plant at a reasonable density; ventilate and reduce humidity; promptly remove diseased leaves, old leaves and diseased plant residues.

(2) Chemical control. Apply pesticide promptly at the early stage of the disease, once every 7-10 days, for 2-3 consecutive treatments, depending on the development of the disease. The selected pesticides 80% jinyimi.myclobutanil, or azoxystrobin, or myclobutanil have good spray control effects.

5. Legume powdery mildew

Legume powdery mildew mainly infects many vegetables such as cowpea, peas, broad beans, hyacinth beans and common beans. This disease occurs commonly in vegetable-growing areas in southern China, and when severe it has a great impact on yield.

Legume powdery mildew mainly harms leaves, and can also infect stems and vines and pods. When leaves are diseased, round yellowish-brown small spots first appear on the back, then expand into irregular purple or brown spots, and a white powdery mold layer is produced on the leaf back or leaf surface; in the later stage, the mold layer on the diseased part ages and turns grayish brown, and black small dots appear among the mold layer. When the disease is severe, multiple spots join together, spread along the veins into powdery bands, and spots also appear on the leaf surface, with the color changing from white to grayish white to purple-brown, spreading over the whole leaf, finally causing the leaves to turn yellow rapidly and fall off. When stems and vines and pods are infected, a white powdery mold layer is produced, which can cause the stems and vines to dry up and the pods to shrink.

The pathogen prefers warm, humid environments. The suitable temperature range for the disease is 15-35°C, and the most suitable climatic conditions are a temperature of 20-30°C and relative humidity of 40-95%. The most susceptible growth stage of the crop is the middle and late stages of flowering and pod setting, and the incubation period of the disease is 3-7 days.

The main peak period of legume powdery mildew is from May to November. In years with relatively high temperatures and much rain, the disease is severe; in weather with alternating dry and wet conditions or large day-night temperature differences and easy dew formation on the leaves at night, the disease is severe; in fields with many years of continuous cropping, low-lying terrain, poor drainage, excessive planting density, poor ventilation and light penetration, and poor growth, the disease is severe.

[Control methods]

(1) Select varieties with strong stress resistance; cultivate on high ridges, plant at a reasonable density, dig ditches for drainage, enhance plant growth, and improve disease resistance; promptly remove old and diseased leaves, and after harvest promptly remove diseased plant residues and take them out of the field for centralized destruction to reduce the source of inoculum in the field. Protected cultivation should strengthen ventilation and air exchange.

(2) Chemical control. At the early stage of the disease, the selected pesticides 80% jinyimi.myclobutanil, or azoxystrobin, or myclobutanil can be sprayed for control, once every 5-7 days, for 2-3 consecutive treatments.

6. Apple powdery mildew

In addition to harming apples, the apple powdery mildew pathogen can also harm Siberian crabapple, sand apple, pingzi, crabapple and others. Apple powdery mildew mainly harms the young branches and young leaves of apple trees, and can also harm buds, flowers and young fruit. After nursery stock is infected, grayish-white patches appear on the top leaves and young stems of the seedlings, as if covered with a white powdery substance. When the disease is severe, the spots expand to the whole leaf, the diseased leaves shrink, gradually turn brown and die. After the top of the new shoot is damaged, leaf expansion is delayed, the emerging leaves are slender and purplish red, the shoot tip is twisted, and after development stops, many dense small black dots are produced on the spots, especially on the young stems and leaf axils.

When the spring temperature gradually rises to between 21-25°C and the relative humidity reaches above 70%, it is favorable for the reproduction and spread of the pathogen. The occurrence of apple powdery mildew has its peak period from April to June, the disease stagnates in the high-temperature season of July to August, spreads again on autumn shoots at the end of August, and gradually declines after September. The disease has two peak periods in a year, completely matching the growth periods of apple tree new shoots.

The occurrence of apple powdery mildew is closely related to climatic conditions, cultivation conditions and varieties. Any year with a warm and dry spring is favorable for the early-stage epidemic of the disease, while a rainy and cool summer and a clear autumn are favorable for the later-stage disease. In low-lying terrain, densely planted orchards, heavy soil, excessive nitrogen fertilizer and insufficient potassium fertilizer, causing a closed canopy and weak branches, the disease is severe. Extensive orchard management, improper pruning, and the inappropriate practice of light pruning and long release increase the number of infected buds and also worsen the occurrence of powdery mildew.

[Control methods]

(1) Strengthen cultivation management, use formula fertilization, avoid excessive nitrogen fertilizer, keep the fruit trees growing robustly, and control irrigation.

(2) Clean the orchard. In combination with winter pruning, cut off diseased shoot tips and diseased buds; re-prune in early spring, cut off newly diseased shoot tips, and destroy them centrally by burning or bury them deeply to prevent the spread of conidia.

(3) Chemical control. Before budding, spray protective pesticides for prevention and protection; in spring at the early stage of the disease, use the selected pesticides 80% jinyimi.myclobutanil, or azoxystrobin, or myclobutanil for spray control, once every 10-20 days, for a total of 3-4 times.

7. Flower powdery mildew

Flowers have very high economic value. In flower cultivation, powdery mildew is an important disease. In recent years, powdery mildew has occurred severely on roses and other flowers, and the affected area in various flower-producing regions has grown larger year by year.

The suitable temperature for the occurrence of flower powdery mildew is 15-25°C. Whether the environment is dry or under high humidity conditions, powdery mildew can spread and transmit.

[Control methods]

The selected pesticides 80% jinyimi.myclobutanil, or azoxystrobin, or myclobutanil have good spray control effects on powdery mildew of various roses and other flowers.

8. Chinese medicinal herb powdery mildew

In the cultivation of Chinese medicinal herbs, powdery mildew is an important disease in production. In recent years, powdery mildew has occurred severely on Chinese medicinal herbs such as Schisandra chinensis, Angelica sinensis, Astragalus membranaceus, Lycium barbarum and Panax notoginseng, and the affected area in various Chinese medicinal herb-producing regions has grown larger year by year.

The suitable temperature for the occurrence of Chinese medicinal herb powdery mildew is 15-25°C. Whether the environment is dry or under high humidity conditions, powdery mildew can spread and transmit.

[Control methods]

At the early stage of the disease, use the selected pesticides 80% jinyimi.myclobutanil, or azoxystrobin, or myclobutanil for spray control.

9. Mango powdery mildew

Mango powdery mildew occurs in Hainan, Guangdong, Guangxi and Yunnan. It can harm mango panicles, young leaves, young shoots and young fruit. On the surface of these young tissues, some scattered white powdery spots first appear, and later the tissue under the spots necroses, forming brown scars. After the panicle is damaged, the flowers stop opening, the flower stalk no longer extends, and then it withers, dries, turns black and falls off. Young leaves are often distorted and fall off when damaged. Young fruit damage causes fruit drop, and on larger young fruit, block-like scars often form.

The disease can occur at 9-32°C and 0-100% relative humidity, and the peak occurrence temperature is around 23°C. The pathogen often survives on old diseased leaves of late-flushing shoots and becomes the source of primary infection. In the following spring, it spreads by wind to newly emerged young leaves and panicles to cause damage. Every year from February to April, during the leaf emergence and flowering period of mango, when high humidity, cloudy skies and relatively low night temperatures occur, this disease is likely to occur and become epidemic.

[Control methods]

On the basis of strengthening cultivation management, spray pesticides at the appropriate time. In ordinary years, spraying once each at the panicle elongation stage, flowering stage and fruit-setting stage can control the damage of this disease; but in severely affected areas or in years of severe infection, it is necessary to spray once every 7 days, increasing the number of sprays. If it rains after spraying, respray. The pesticide 80% jinyimi.myclobutanil wettable powder at 2500 times has a special effect on controlling mango powdery mildew.

10. Wheat powdery mildew

Damage symptoms: at the initial stage of the disease, white mold spots appear on the leaf surface, then gradually expand into nearly round to oval white mold spots. The surface of the mold spots has a layer of white powder, which immediately scatters when subjected to external force or vibration.

These powdery substances are the mycelium and conidia of this fungus. In the later stage, the mold layer on the diseased part turns grayish white to light brown, and small black grains the size of a needle tip are scattered on the spots, namely the cleistothecia of the pathogen.

Peak period of the disease: mid-to-late March to late April, with differences among different regions

[Control methods]

(1) Select disease-resistant varieties.

(2) Advocate the application of compost fermented with effective microorganisms or decomposed organic fertilizer, adopt formula fertilization techniques, appropriately increase phosphorus and potassium fertilizer, and plant at a reasonable density according to variety characteristics and soil fertility. In the wheat regions of southern China, drain promptly after rain to prevent moisture retention. In the wheat regions of northern China, irrigate at the appropriate time to enhance the host's disease resistance.

(3) In areas where self-sown wheat seedlings overwinter in summer, promptly remove self-sown wheat before autumn sowing of winter wheat, which can greatly reduce the source of inoculum for autumn seedlings.

(4) At present, the main effective therapeutic pesticides on the market for controlling powdery mildew are: heterocyclic compounds (ethirimol, ethirimol sulfamate), triazoles (triadimefon, hexaconazole, propiconazole, tebuconazole, epoxiconazole, etc.) and strobilurin compounds (azoxystrobin, kresoxim-methyl, etc.).

1. The heterocyclic compounds ethirimol and ethirimol sulfamate have very good control effects, but resistance develops too quickly.

2. Triazole pesticides such as hexaconazole, tebuconazole and epoxiconazole have relatively good preventive effects on wheat powdery mildew, but their therapeutic effects are unstable. When wheat powdery mildew has not occurred or is at the early stage, these pesticides can be selected for control. At present, the wheat powdery mildew pathogen in many areas has strong resistance to triazole fungicides such as triadimefon, tebuconazole and hexaconazole. Even if the dosage is increased substantially, the control effect on powdery mildew is still not stable enough.