Prevention and treatment of cucumber target spot disease spot with target eye leaf in greenhouse

Cucumber target spot is a kind of fungal disease. Cladosporium is the pathogen, also known as clavulosporium leaf spot. In recent years, with the continuous development of cucumber cultivation in greenhouse, the disease is getting worse year by year, which has become an important leaf disease of cucumber in greenhouse, and may cause damage to tomato and other vegetables.

Cucumber target spot

After the peak period of cucumber target spot disease, the middle and lower leaves first occurred, and yellow, round and sunken spots were formed on the front of the leaves, and the back was waterlogged, commonly known as small yellow spot, which expanded into round or nearly round brown spots of different sizes. In the later stage, the color in the middle of the lesion became lighter, and there was an obvious bull's-eye in the center of the spot, which got the name target spot disease. Affected by air temperature, humidity and cucumber disease resistance, the size, color and mildew layer of the disease spot will change greatly. when the humidity is high, the disease spot will produce grayish brown mildew on the front and back. When the disease is serious, the disease spots are fused, the leaves are withered and yellow, and oval grayish brown spots appear on the stem vine and petiole.

Cucumber target spot is easily misdiagnosed as downy mildew or bacterial angular spot. When distinguishing, we can pay attention to the following characteristics: the edge of the disease spot of downy mildew and bacterial angular spot is flooded, especially in the morning. The boundary of the target spot is clear; the expansion of the disease spot of downy mildew and bacterial angular spot is polygonal, while the spot of the target spot is slightly round (especially in the early stage of the disease); when the humidity is high, the downy mildew spot grows a gray-black mold layer on the back of the leaf, and the bacterial angular spot is overflowed with milky white bead-like bacteria pus on the back of the leaf, and there are white marks after drying, and the target spot will produce a gray-brown milky mildew layer on both sides of the leaf. In addition, leaf spot disease caused by Alternaria or pseudocercospora fungi may occur on cucumbers, which need not be strictly distinguished because the control techniques are similar.

Cucumber target spot disease could spread with seeds including grafted pumpkin seeds, but more often, conidia, chlamydospores and mycelium overwintered in the soil with cucumber disease residues, and conidia were produced the following year, which were spread by air flow and raindrops. The disease is an air-borne disease with high temperature and high humidity. The temperature difference between day and night is large, the dew time is long, the plant is weak, and the disease is serious in the land where nitrogen fertilizer is applied.

Control target spot: soak cucumber seeds and grafted black-seeded pumpkin seeds in 55 ℃ warm water for half an hour; rotate with celery, water radish, tobacco, balsam pear or non-melon crops for more than two years and pay attention to thoroughly remove the diseased and residual plants in the field and turn the soil deeply; avoid partial application of nitrogen fertilizer, increase phosphorus and potassium fertilizer, and apply appropriate amount of boron fertilizer. After watering, pay attention to ventilation and dehumidification, at the initial stage of the disease, remove the diseased leaves and carry out chemical control in time. Different from downy mildew and bacterial angular spot, there are many kinds of agents to control target spot disease, including broad-spectrum fungicides mancozeb, carbendazim, thiophanate methyl, chlorothalonil, triazole propiconazole, difenoconazole, flusilazole, tebuconazole, imidazole fungicides prochloraz, flurobupromazol, methoxy acrylate carbendazim and pyrazole. Dimethimide agents such as isofloxide, quinoline copper, amiceda, etc. As bacteria are easy to develop drug resistance, so reduce the number of drug use as much as possible, rotate the use of different types of agents and use compound agents.