Recently, Daxing District Plant Protection Station carried out a general survey of the occurrence of pests and diseases of vegetables in protected areas and found that cucumbers in the greenhouse developed powdery mildew, downy mildew, and sclerotinia diseases. Insect pests were mainly aphids and whiteflies, and the incidence rate of diseased land was 5%. -10%, the rate of diseased plants in individual severe plots reached 80%-90%, reminding the vegetable farmers to investigate and treat them in time.

Symptoms and Causes of Three Diseases

◆ Powdery mildew, commonly known as "white hair," is a common invasive disease of cucumber in winter greenhouses. Any part of the plant can be diseased, with the most severe leaves, followed by petiole and stem, generally not harm the fruit. At temperatures of 16°C-24°C and relative humidity of 75%, it is beneficial to the occurrence and prevalence of powdery mildew; if the foliage has water droplets, the bacteria will break up and die; high temperature, high humidity and no condensation or management Improperly, when the growth of cucumber declines, powdery mildew occurs seriously.

◆ Downy mildew, commonly known as “black hair” and “wild horse dried,” will cause serious damage if it is not controlled in time. Mainly in the leaves, mostly after the flowering results, began to produce water spots like spots, after expansion, due to the limitations of the veins were yellow-brown lesions of the polygon, when the wet leaves long purple mold. It generally spreads upward from the lower leaves. In severe cases, the lesions communize with each other and finally the entire leaf is shriveled. The optimum temperature for downy mildew disease is 16°C-24°C, and the suitable humidity is 85% or more, especially when the leaves have water film. Humidity is less than 70% and germ spores are difficult to germinate and infest.

◆ Sclerotinia The disease mainly affects fruits and vine vines. Fruits are mostly found in the streaks. They are immersed in water and rot. They grow white thick mycelium, and the hyphae become entangled in black sclerotia. When the stalk is infected, it begins to fade in the stem or the main lateral branch of the sub-branch at the near-ground surface. It gradually enlarges and appears light brown. Under high humidity conditions, the stem is soft and rot, and white cotton-like mycelium grows. . The stem of the stem is damaged and rotted hollow, or split and dried. The epidermis of the stem is longitudinally split, but the xylem is not spoiled. Therefore, the plants do not show wilting, but the upper leaves of the diseased part, withered and wilted, are dead. When petiole, leaf and young fruit become infected, they begin to appear water-soaked and rapidly soften, and then a large number of white mycelium grows. Mycelium densely forms the black rat fecal nucleus. Relative humidity higher than 85%, temperature 15 °C -20 °C conducive to sclerotial germination and mycelial growth, invasive and ascendant disk production.

Identification points

â–  The early symptoms of lesions of downy mildew are easily confused with keratoses

Pathogens Different bacterial keratoses are a bacterial disease, while downy mildew is a fungal disease. There are essential differences between the two, and medications are of course different.

Lesion size varies Bacterial keratopathia lesions are relatively small, usually 4-8 mm in diameter, lighter in color, grayish in color, often with perforation in later stages; lesions in downy mildew are usually large, typically 10-16 mm in diameter The color is relatively dark, yellow-brown, and the lesion is not perforated.

Symptoms of the leaves on the back of the rhesus maculosa are different when the humidity is high, and sometimes the milky pus is secreted. On the back of the downy leaf, there is a layer of gray and black mold.

At the site of damage, different downy mildews generally only damage the leaves; in addition to leaf damage, keratoses also injure the petioles, tendrils, fruits, and vine vines. The lesions extend longitudinally along the stem sulcus to form streak, and when the disease is severe, the stems are longitudinally split. Diseased melons smell bad.

When the symptoms are inaccurate, a simple method can be used to identify the disease: remove the diseased leaf and place it in a clean plastic bag with a little water, and place it at 15°C-20°C for 24 hours. Mold production is downy mildew, no black mold and bacterial pus overflow is bacterial angular spot.

â– Gray mold and Sclerotinia are easily confused

Conidia body color of different sclerotia is white cotton flocculent mycelium, gray mold is gray black mold, which is one of the important characteristics of distinguishing between the two types of bacteria.

The initial infection of the main susceptible site is different from the initial infection of the sclerotia at the base or at the tiller of the stem, or at the leaf margin or stalk, with a small amount of white mold. The initial infection of the gray mold is generally the residual flower part. Gray mycelium.

Infection after the performance of different Sclerotinia in the site of serious infection easy to produce sclerotia; Botrytis cinerea is not easy to generate sclerotia. Botrytis cinerea is easy to generate "V"-shaped rosy and large brown spots on the diseased leaves, and gray molds on the fruit pedicles or umbilicus; sclerotia directly forms rot lesions on the entire fruit surface after infection by the stalks.

Control methods

Choose disease-resistant varieties.

Agricultural measures: Avoid excessive application of nitrogen fertilizers and increase phosphorus and potassium fertilizers. Ventilation and dehumidification in the greenhouse are timely. Implement rotations, strengthen management, and eliminate sick organizations.

Covering the straw curtains or insulation at night, the conditions of the greenhouses should take other measures to increase the temperature within the shed, during the day and fine weather should be properly ventilated; timely cleaning of the shed film, increase the amount of light, and promote the temperature of the greenhouse.

? The use of flood irrigation of the greenhouse should pay attention to timely cultivator after watering, at the same time, to avoid the water inside the shed.

? timely removal of diseased leaves and diseases in the field, especially in the lower part of the leaves and the lower part of the cucumber, diseased leaves and fruit with plastic bags concentrated removal to the shed, so as not to cause disease and then infect.

Early onset of drug control

● During the cultivation of powdery mildew in greenhouses, 250 grams of sulfur powder, 500 grams of sawdust, or 250 grams of 45% chlorothalonil smoke agent are used per 100 cubic meters of space before planting. To kill the bacteria inside the shed.

Before the onset of the disease, spray 800 times of green milk copper to protect the leaves. In the early stage of disease, use 50% carbendazim WP 800 times or 75% chlorothalonil wettable powder 600-800 times, or 25% triadimefon WP 2000 times, or 50% carbendazim (Cuibei) water dispersed granules 13-20 grams? Mu, or 40% Fuxing 4000-5000 times liquid, or 10% Shigao 1500-2000 times spray control.

The key to prevention of powdery mildew is early prevention and reduction of disease sources. The spray should be thoughtful, so that it can spray the drug evenly and it will not cause downy mildew due to the excessive increase of air humidity. The use of various agents alternately prevents the use of a single agent for a long period of time to make the bacteria resistant.

● The control of downy mildew can be sprayed with 72.2% Preclosure 800 times, or 58% Ledomil WP 500 times, or 64% WP wettablet 400 times, every 7-10 Spray once a day. In order to reduce the humidity in the greenhouse, 45% of the chlorothalonil aerosol can be used, 200-250 g per mu, placed in 4-5 indoor places, ignited by dark fire, smoked in closed sheds for one night, and released in the morning, once every 7 days.

● Sclerotinia can be controlled with 50% Sulfatine WP 1500 times, or 50% Epstein WP 1000 times, or 50% Nylon WP 1000 times, or 20% A. LBK 1000 times, or 50% acetaminophen wettable powder 1500 times, 70% thiophanate-methyl WP 1000 times spray at full bloom, once every 8-9 days, continuous control 3-4 times. In severe cases, in addition to the daily spray, the above-mentioned fungicides can also be diluted 50 times and smeared in the diseased part of guava to suppress the disease. Haze or overcast and snowy weather is controlled by smoke, with 10% fast-king smoke agent, or 45% chlorothalonil smoke agent, 250 grams per mu, smoked 1 night, every 8-10 days, continuous control 3-4 Times. Sprinkle 5% chlorothalonil dust at 1 kg/acre.

● Aphid and whitefly prevention and control Aphid and whitefly are fast-growing, and the population is large. Except for sucking leaf sap to spread the virus, the secretion of honeydew also seriously affects the quality of cucumber, resulting in reduced production. Use 10% imidacloprid wettable powder 2000 spray control, or 25% Aktai water dispersant 1500-2000 spray control, once every 7 days, once used 3-4 times to receive better control effect.

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