The prevention and cure of cucumber target spot

Cucumber target spot disease is a kind of fungal disease. The pathogen is Corynepora cubensis. So it is also called Corynespora. It has been reported in various parts of China in the past, but it is not very serious. In recent years, with the continuous development of protected land cultivation, the condition has been increasing year by year, and it has become an important leaf disease of cucumber production in protected areas, and it may cause damage to various vegetables such as tomatoes.

Cucumber target spot disease mostly occurs after cucumber melon period, first from the middle and lower leaves, the formation of yellow, round, concave spots in the front of the blade, the back of water spots, commonly known as small yellow spot disease. Gradually expand into round or near-circular brown spots of varying sizes. The color in the middle of the lesion gradually became lighter, and there was an obvious eye-like bull's-eye in the center of the lesion, so it was named the target spot. Affected by temperature, humidity, and cucumber disease resistance, the lesion size, color, and mold layer will be greatly changed. The majority of diameters are 8 to 15 mm. When the humidity is high, the lesions on both sides of the lesions are pale brownish moldy. When the disease is severe, the lesions fuse, the leaves are yellow, and oval grayish brown spots appear on stems and petioles.

Cucumber target spot disease in the field is easily misdiagnosed as downy mildew or bacterial angular spot disease. The following characteristics can be noticed in the identification: the lesions of downy mildew and bacterial keratoses are immersed in water, especially in the morning. The typical target spot lesions have clear boundaries; the lesions of downy mildew and bacterial keratoses are limited by the veins, they are polygonal, and the spots of the target lesions are slightly rounded (especially at the beginning of the disease. Period;) When the humidity is high, downy mildew spots grow on the back of the leaves with a layer of grayish black mold, which is sparse. Bacterial keratoses have milky white muddy watery bacilli on the back of leaves, white marks after drying, and target spots. Lesions on the front and back produce brown-brown mildew. In addition, leaf spot disease caused by Alternaria or Pseudocercospora may also occur on cucumbers. Since the control techniques are similar, it is not necessary to strictly distinguish them.

Cucumber target spot disease can spread with seeds, including grafted pumpkin seed, but more often the pathogens use conidia, chlamydospore, or mycelium to overwinter in the soil with the diseased body, producing conidia the next year, either through airflow or Raindrops spread. The disease is a high-temperature, high-humidity airborne disease. Large temperature difference between day and night, long dew condensation time, debilitating plants, and heavy nitrogenous fertilizers.

The following measures shall be taken to prevent and treat target spot diseases: Soak cucumber seeds and grafted black-skinned squash seeds for 30 minutes with warm water at 55°C; rotate for more than two years with celery, radish, tobacco, bitter gourd or non-melon crops and pay attention to the thorough removal of fields The diseased plants will be deeply turned into the soil; partial application of nitrogen fertilizers, application of phosphorus and potassium fertilizers, and appropriate application of boron fertilizer. After the watering, attention should be paid to excretion and evacuation, diseased leaves should be removed at the early stage of disease, and chemical prevention should be carried out in the early stage of disease. The agents for preventing and treating target spot disease are different from those for controlling downy mildew and bacterial keratoderma. There are many types that can be selected, including the broad spectrum fungicide mancozeb, carbendazim, thiophanate-methyl, chlorothalonil. , Triazoles Propiconazole, difenoconazole, fluorosiliconazole, tebuconazole, imidazole bactericides prochloraz, fluconazole, strobilurin methoxybenzoate, pyraclostrobin Ester, dimethyl imides, iprodione, quinoline copper, amidida, etc. Because germs are very likely to produce drug resistance, it is necessary to reduce the number of medications as much as possible, rotate different types of medicaments and use reconstituted medicaments.

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