Diagnosis and control of cucumber target spot disease

Cucumber target spot disease is a fungal disease, and the pathogen is C. cinerea, so it is also called Corynebacterium leaf spot.

Symptoms and occurrence

Cucumber target spot disease occurs mostly after cucumber melon stage, first occurs from the middle and lower leaves, forming yellow, round, concave spots on the front of the leaves, and water stain on the back, commonly known as small yellow spot disease. It gradually expands into round or nearly round brown lesions of varying sizes. In the late stage, the color of the lesion is lighter, and there is a prominent eye-shaped target in the center of the lesion, hence the name target disease. Affected by temperature, etc., the size, color and mildew of the lesions will change greatly. Most of the diameters are 8 to 15 mm. When the humidity is high, the lesions are both gray and brown. When the disease is serious, the lesions are fused, the leaves are yellow, and the oval-brown lesions appear on the stems and petioles.

Cucumber target spot can be transmitted with seeds, including grafted pumpkin seeds, but more often the bacteria are overgrowth in the soil with conidia, chlamydospores or mycelium with diseased bodies, and conidia are produced in the following year, by airflow or Raindrops spread. The temperature difference between day and night is large, the condensation time is long, the plants are weak, and the plots with partial nitrogen fertilizer are seriously affected.

Differential diagnosis

Cucumber target spot disease in the field is easily misdiagnosed as downy mildew or bacterial keratosis. You can pay attention to the following characteristics when identifying:

1. The edge of the lesions of downy mildew and bacterial angular spot are water-soaked, especially in the morning. The typical target spot disease has a clear boundary.

2. Downy mildew and bacterial keratosis are limited by the veins and will be polygonal, while the target plaques are slightly rounded (especially in the early stage of the disease).

3. When the humidity is high, the downy mildew lesions grow grayish black mold layer on the back of the leaf, which is sparse. The bacterial angular spot disease has milky white turbid watery beaded pus in the back of the leaf, white marks after drying, target spot disease A gray-brown mold layer is formed on the front and back of the lesion.

4. Leaf spot disease caused by Alternaria or Pseudomonas spp. may occur on cucumber. Because the control techniques are similar, it is not necessary to distinguish strictly.


Soak cucumber seeds and grafted black seed pumpkin seeds in warm water at 1.55 ° C for 30 minutes.

2. Rotate with celery, radish, tobacco, bitter gourd or non-melon crops for more than 2 years and pay attention to completely remove the diseased plants in the field and then deepen the soil.

3. Avoid partial application of nitrogen fertilizer, increase application of phosphorus and potassium fertilizer, and apply boron fertilizer in an appropriate amount.

4. Chemical control in the early stage of the disease. The agent for controlling target spot disease is different from the control of downy mildew and bacterial angular spot disease. There are many types to choose from, including broad-spectrum fungicides, mancozeb, carbendazim, thiophanate-methyl, and chlorothalonil. Triazole drugs propiconazole, difenoconazole, flusilazole, tebuconazole, imidazole fungicide prochloraz, fluconazole, methoxy acrylate esters, pyraclostrobin Ester; diimide-based agent, iprodione, and quinoline copper, amishida, and the like.

5. To minimize the number of medications, rotate different types of medications and use a combination of medications.

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